Evolutionary thought, the conception that species change over time, has roots in antiquity, in the ideas of the ancient
GreeksAncient Greece is the civilisation belonging to the period of Greek history lasting from the Greek Dark Ages ca. 1100 BC and the Dorian invasion, to 146 BC and the Roman conquest of Greece after the Battle of Corinth. It is generally considered to be the seminal culture which provided the...
,
RomansAncient Rome was a civilization that grew out of a small agricultural community founded on the Italian Peninsula as early as the 10th century BC. Located along the Mediterranean Sea, it became one of the largest empires in the ancient world....
, and Chinese as well as in medieval Islamic science. However, until the 18th century, Western biological thinking was dominated by
essentialismIn philosophy, essentialism is the view that, for any specific kind of entity, there is a set of characteristics or properties all of which any entity of that kind must possess, and therefore all things can be precisely defined or described...
, the belief that every species has essential characteristics that are unalterable. This began to change when, during the
EnlightenmentThe Age of Enlightenment, or simply The Enlightenment, is a term used to describe a time in Western philosophy and cultural life, centered upon the eighteenth century, in which reason was advocated as the primary source and legitimacy for authority....
, evolutionary cosmology and the mechanical philosophy spread from the physical sciences to natural history. Naturalists began to focus on the variability of species; the emergence of
paleontologyPaleontology
[from Greek: παλαιός "old, ancient", ὄν, ὀντ- "being, creature", and λόγος "speech, thought"] is the study of prehistoric life, including organisms' evolution and interactions with each other and their environments...
with the concept of
extinctionIn biology and ecology, extinction is the end of an organism or group of taxa. The moment of extinction is generally considered to be the death of the last individual of that species...
further undermined the static view of nature. In the early 19th century,
Jean-Baptiste LamarckJean-Baptiste Pierre Antoine de Monet, Chevalier de la Marck , often just known as 'Lamarck', was a French soldier, naturalist, academic and an early proponent of the idea that evolution occurred and proceeded in accordance with natural laws.Lamarck fought in the Pomeranian War with Prussia, and...
proposed his theory of the
transmutation of speciesTransmutation of species was a term used by Jean Baptiste Lamarck in 1809 for his theory that described the altering of one species into another. It was one of the names commonly used for evolutionary ideas in the 19th century before Charles Darwin published On The Origin of Species...
, the first fully formed scientific theory of
evolutionIn biology, evolution is change in the genetic material of a population of organisms from one generation to the next. Though changes produced in any one generation are normally small, differences accumulate with each generation and can, over time, cause substantial changes in the population, a...
.
In 1858,
Charles DarwinCharles Robert Darwin FRS was an English naturalist who realised and presented compelling evidence that all species of life have evolved over time from common ancestors, through the process he called natural selection...
and
Alfred Russel WallaceAlfred Russel Wallace, OM, FRS was a British naturalist, explorer, geographer, anthropologist and biologist...
published a new evolutionary theory, which was explained in detail in Darwin's
On the Origin of Species (1859). Unlike Lamarck, Darwin proposed
common descentA group of organisms is said to have common descent if they have a common ancestor. In modern biology, it is generally accepted that all living organisms on Earth are descended from a common ancestor or ancestral gene pool....
and a branching
tree of lifeCharles Darwin believed that phylogeny, the ascent of all species through time, was expressible as a metaphor he termed the Tree of Life. The modern development of this idea is called the Phylogenetic tree.- Early Trees of Life :...
. The theory was based on the idea of
natural selectionNatural selection is the process by which heritable traits that make it more likely for an organism to survive and successfully reproduce become more common in a population over successive generations...
, and it synthesized a broad range of evidence from animal husbandry, biogeography, geology, morphology, and embryology.
The debate over Darwin's work led to the rapid acceptance of the general concept of evolution, but the specific mechanism he proposed, natural selection, was not widely accepted until revived in developments in the 1930s which were cemented in the 1940s. Most biologists argued that other factors were responsible for evolution, such as
inheritance of acquired characteristicsThe inheritance of acquired traits is a hypothesis about a mechanism of heredity by which changes in physiology acquired over the life of an organism may purportedly be transmitted to offspring...
(neo-Lamarckism), an innate drive for change (
orthogenesisOrthogenesis, orthogenetic evolution, progressive evolution or autogenesis, is the hypothesis that life has an innate tendency to move in a unilinear fashion due to some internal or external "driving force". The hypothesis is based on essentialism and cosmic teleology and proposes an intrinsic...
), or sudden large mutations (
saltationismIn biology, saltation is a sudden change from one generation to the next, that is large, or very large, in comparison with the usual variation of an organism...
). The synthesis of natural selection with
Mendelian geneticsMendelian inheritance is a set of primary tenets relating to the transmission of hereditary characteristics from parent organisms to their children; it underlies much of genetics. They were initially derived from the work of Gregor Mendel published in 1865 and 1866 which was "re-discovered" in...
during the 1920s and 1930s founded the new discipline of
population geneticsPopulation genetics is the study of the allele frequency distribution and change under the influence of the four evolutionary processes: natural selection, genetic drift, mutation and gene flow. It also takes account of population subdivision and population structure in space. As such, it attempts...
. Throughout the 1930s and 1940s, population genetics became integrated with other biological fields, resulting in a widely applicable theory of evolution that encompassed much of biology—the
modern evolutionary synthesisThe modern evolutionary synthesis is a union of ideas from several biological specialties which forms a logical account of evolution. This synthesis has been accepted by nearly all working biologists...
.
Following the establishment of
evolutionary biologyEvolutionary biology is a sub-field of biology concerned with the origin of species from a common descent and descent of species, as well as their change, multiplication and diversity over time. Someone who studies evolutionary biology is known as an evolutionary biologist...
, studies of
mutationIn biology, a mutation is a randomly derived change to the nucleotide sequence of the genetic material of an organism.Mutations can be caused by copying errors in the genetic material during cell division, or by exposure to mutagens , or can be induced by the organism itself, by cellular processes...
and
variationGenetic diversity is a level of biodiversity that refers to the total number of genetic characteristics in the genetic makeup of a species. It is distinguished from genetic variability, which describes the tendency of genetic characteristics to vary....
in natural populations, combined with
biogeographyBiogeography is the study of the distribution of biodiversity over space and time. It aims to reveal where organisms live, and at what abundance....
and
systematicsBiological systematics is the study of the diversification of life on the planet Earth, both past and present, and the relationships among living things through time. Relationships are visualized as evolutionary trees...
, led to sophisticated mathematical and causal models of evolution. Paleontology and
comparative anatomyComparative anatomy is the study of similarities and differences in the anatomy of organisms. It is closely related to evolutionary biology and phylogeny .-Description:Two major concepts of comparative anatomy are:...
allowed more detailed reconstructions of the history of life. After the rise of
molecular geneticsMolecular genetics is the field of biology that studies the structure and function of genes at a molecular level. The field studies how the genes are transferred from generation to generation. Molecular genetics employs the methods of genetics and molecular biology. It is so-called to...
in the 1950s, the field of
molecular evolutionMolecular evolution is the process of evolution at the scale of DNA, RNA, and proteins. Molecular evolution emerged as a scientific field in the 1960s as researchers from molecular biology, evolutionary biology and population genetics sought to understand recent discoveries on the structure and...
developed, based on protein sequences and immunological tests, and later incorporating RNA and DNA studies. The
gene-centered view of evolutionThe gene-centered view of evolution, gene selection theory or selfish gene theory holds that natural selection acts through differential survival of competing genes, increasing the frequency of those alleles whose phenotypic effects successfully promote their own propagation...
rose to prominence in the 1960s, followed by the
neutral theory of molecular evolutionThe neutral theory of molecular evolution is an influential theory, which was introduced with effect by Motoo Kimura in the late 1960s and early 1970s. The theory states that the vast majority of evolutionary changes at the molecular level are caused by random drift of selectively neutral mutants...
, sparking debates over
adaptationismAdaptationism is a set of methods in the evolutionary sciences for distinguishing the products of adaptation from traits that arise through other processes. It is employed in fields such as ethology and evolutionary psychology that are concerned with identifying adaptations...
, the
units of selectionA unit of selection is a biological entity within the hierarchy of biological organisation that is subject to natural selection. For several decades there has been intense debate among evolutionary biologists about the extent to which evolution has been shaped by selective pressures acting at...
, and the relative importance of
genetic driftGenetic drift or allelic drift is the change in the relative frequency with which a gene variant occurs in a population due to random sampling and chance: the alleles in offspring are a random sample of those in the parents, and chance has a role in determining whether a given individual survives...
versus natural selection. In the late 20th century, DNA sequencing led to
molecular phylogeneticsMolecular phylogenetics, also known as molecular systematics, is the use of the structure of molecules to gain information on an organism's evolutionary relationships. The result of a molecular phylogenetic analysis is expressed in a phylogenetic tree....
and the reorganization of the tree of life into the
three-domain systemThe three-domain system is a biological classification introduced by Carl Woese in 1990 that divides cellular life forms into archaea, bacteria, and eukaryote domains. In particular, it emphasizes the separation of prokaryotes into two groups, originally called Eubacteria and Archaebacteria...
. In addition, the newly recognized factors of
symbiogenesisSymbiogenesis is the merging of two separate organisms to form a single new organism. The idea originated with Konstantin Mereschkowsky in his 1926 book Symbiogenesis and the Origin of Species, which proposed that chloroplasts originate from cyanobacteria captured by a protozoan...
and
horizontal gene transferHorizontal gene transfer , also Lateral gene transfer , is any process in which an organism incorporates genetic material from another organism without being the offspring of that organism. By contrast, vertical transfer occurs when an organism receives genetic material from its ancestor, e.g...
introduced yet more complexity into evolutionary history.
Greeks
Greek philosophers discussed ideas that involved forms of organic evolution.
AnaximanderAnaximander was a pre-Socratic Greek philosopher who lived in Miletus, a city of Ionia. He belonged to the Milesian school and learned the teachings of his master Thales. He succeeded him and became the second master of that school where he counted Anaximenes and Pythagoras amongst his...
(c. 610–546 BC) proposed that life had originally developed in the sea and only later moved onto land, and
EmpedoclesEmpedocles was a Greek pre-Socratic philosopher and a citizen of Agrigentum, a Greek city in Sicily. Empedocles' philosophy is best known for being the origin of the cosmogenic theory of the four classical elements. He also proposed powers called Love and Strife which would act as forces to bring...
(c. 490–430 BC) wrote of a non-supernatural origin for living things. Empedocles suggested that
adaptationAdaptation is the process whereby a population becomes better suited to its habitat. This process takes place over many generations, and is one of the basic phenomena of biology....
did not require an organizer or final cause. Aristotle summarized his idea: "Wherever then all the parts came about just what they would have been if they had come to be for an end, such things survived, being organized spontaneously in a fitting way; whereas those which grew otherwise perished and continue to perish…" although Aristotle himself rejected this view.
PlatoPlato , was a Classical Greek philosopher, mathematician, writer of philosophical dialogues, and founder of the Academy in Athens, the first institution of higher learning in the Western world...
(c. 428–348 BC) was, in the words of biologist and historian Ernst Mayr, "the great antihero of evolutionism", as he established the philosophy of
essentialismIn philosophy, essentialism is the view that, for any specific kind of entity, there is a set of characteristics or properties all of which any entity of that kind must possess, and therefore all things can be precisely defined or described...
, which he called the
Theory of FormsPlato's theory of Forms or theory of Ideas asserts that non-material abstract forms , and not the material world of change known to us through sensation, possess the highest and most fundamental kind of reality. When used in this sense, the word form is often capitalized...
. This theory holds that objects observed in the real world are only
reflections of a limited number of
essenceIn philosophy, essence is the attribute or set of attributes that make an object or substance what it fundamentally is, and which it has by necessity, and without which it loses its identity. Essence is contrasted with accident: a property that the object or substance has contingently, without...
s (
eide). Variation is merely the result of an imperfect reflection of these constant essences. In his
TimaeusTimaeus is a theoretical treatise of Plato in the form of a Socratic dialogue, written circa 360 BC. The work puts forward speculation on the nature of the physical world. It is followed by the dialogue Critias....
, Plato set forth the idea that the
DemiurgeDemiurge in philosophical and religious language is a term for a creator deity, responsible for the creation of the Universe.In the sense of a divine creative principle...
had created the
cosmosIn its most general sense, a cosmos is an orderly or harmonious system. It originates from a Greek term κόσμος meaning "order, orderly arrangement, ornaments," and is the antithetical concept of chaos. Today the word is generally used as a synonym of the word Universe . The words cosmetics and...
and everything in it because, being good, and hence, "… free from jealousy, He desired that all things should be as like Himself as they could be". The creator created all conceivable forms of life, since "… without them the universe will be incomplete, for it will not contain every kind of animal which it ought to contain, if it is to be perfect". This idea, that all potential forms of life are essential to a perfect creation, is called the
plenitude principleThe plenitude principle or principle of plenitude asserts that everything that can happen will happen.The historian of ideas Arthur Lovejoy was the first to discuss this philosophically important Principle explicitly, it back to Aristotle, who said that no possibilities which remain eternally...
, and greatly influenced Christian thought.
AristotleAristotle was a Greek philosopher, a student of Plato and teacher of Alexander the Great. He wrote on many subjects, including physics, metaphysics, poetry, theater, music, logic, rhetoric, politics, government, ethics, biology, and zoology.Together with Plato and Socrates , Aristotle is one of...
(384–322 BC), one of the most influential of the Greek philosophers, is the earliest natural historian whose work has been preserved in any real detail. His writings on biology were the result of his research into natural history on and around the isle of
LesbosLesbos is a Greek island located in the northeastern Aegean Sea. It has an area of 1632 km² with 320 kilometres of coastline, making it the third largest Greek island and the largest of the numerous Greek islands scattered in the Aegean. Administratively, it forms part of the Lesbos Prefecture...
, and have survived in the form of four books, usually known by their
LatinLatin is an Italic language originally spoken in Latium and Ancient Rome. Through the Roman conquest, Latin spread throughout the Mediterranean and a large part of Europe...
names,
De animaOn the Soul is a major treatise by Aristotle on the nature of living things. His discussion centres on the kinds of souls possessed by different kinds of living things, distinguished by their different operations...
(on the essence of life),
Historia animaliumHistory of Animals is a zoological natural history text by Aristotle.The work consists of lengthy descriptions of countless species of fish, shellfish, and other animals and their anatomies...
(inquiries about animals),
De generatione animaliumGeneration of Animals is a text by Aristotle.-Arabic translation:...
(reproduction), and
De partibus animalium (anatomy). Aristotle's works contain some remarkably astute observations and interpretations, along with sundry myths and mistakes—reflecting the uneven state of knowledge during his time. However, for
Charles SingerCharles Joseph Singer was a British historian of science and medicine.-Early years:Singer was born in Camberwell in London, where his father Simeon Singer was a minister and Hebraist. He was educated at City of London School, University College London, and Magdalen College, Oxford...
, "Nothing is more remarkable than [Aristotle's] efforts to [exhibit] the relationships of living things as a
scala naturæ." This
scala naturæ, described in
Historia animalium, classified organisms in relation to a hierarchical "Ladder of Life" or "Chain of Being", placing them according to their complexity of structure and function, relative to organisms that showed greater vitality and ability to move described as "higher organisms".
Chinese
Ideas on evolution were expressed by ancient
Chinese thinkersChinese philosophy is philosophy written in the Chinese tradition of thought. Chinese philosophy has a history of several thousand years; its origins are often traced back to the Yi Jing , an ancient compendium of divination, which uses a system of 64 hexagrams to guide action...
such as
ZhuangziZhuangzi was an influential Chinese philosopher who lived around the 4th century BCE during the Warring States Period, corresponding to the Hundred Schools of Thought philosophical summit of Chinese thought...
(Chuang Tzu), a Taoist philosopher who lived around the 4th century BC. According to
Joseph NeedhamNoel Joseph Terence Montgomery Needham, CH, FRS, FBA , also known as Li Yuese , was a British academic and sinologist known for his research and writing on the history of Chinese science. He was elected a fellow of the Royal Society in 1941; and he was elected a fellow of the British Academy in 1971...
,
TaoismDaoism refers to a variety of related philosophical and religious traditions and concepts that have influenced East Asia for over two millennia and the West for over two centuries. The word 道, Tao , means "path" or "way", although in Chinese folk religion and philosophy it has taken on more...
explicitly denies the fixity of biological species and Taoist philosophers speculated that species had developed differing attributes in response to differing environments. Humans, nature and the heavens are seen as existing in a state of "constant transformation" known as the
TaoTao is a concept found in Taoism, Confucianism, and more generally in ancient Chinese philosophy. While the character itself translates as 'way', 'path', or 'route', or sometimes more loosely as 'doctrine' or 'principle', it is used philosophically to signify the fundamental or true nature of the...
, in contrast with the more static view of nature typical of Western thought.
Romans
Titus
LucretiusTitus Lucretius Carus was a Roman poet and philosopher. His only known work is the epic philosophical poem on Epicureanism De rerum natura, translated into English as On the Nature of Things or "On the Nature of the Universe"....
Carus (d. 50 BC), the Roman philosopher and atomist, wrote the poem
On the Nature of ThingsDe rerum natura is a first century BC epic poem by the Roman poet and philosopher Lucretius with the goal of explaining Epicurean philosophy to a Roman audience. The poem, written in dactylic hexameter, is divided into six books, and concentrates heavily on Epicurean physics...
(
De rerum natura), which provides the best surviving explanation of the ideas of the Greek Epicurean philosophers. It describes the development of the cosmos, the Earth, living things, and human society through purely naturalistic mechanisms, without any reference to supernatural involvement.
On the Nature of things would influence the cosmological and evolutionary speculations of philosophers and scientists during and after the
RenaissanceThe Renaissance was a cultural movement that spanned roughly the 14th to the 17th century, beginning in Florence in the Late Middle Ages and later spreading to the rest of Europe...
.
Augustine of Hippo
In line with earlier Greek thought, the 4th century
bishopA bishop is an ordained or consecrated member of the Christian clergy who is generally entrusted with a position of authority and oversight. Within the Roman Catholic, Eastern Orthodox, Oriental Orthodox Churches, in the Assyrian Church of the East, in the Independent Catholic Churches, and in the...
and theologian, St. Augustine of Hippo, wrote that the creation story in Genesis should not be read too literally. In his book
De Genesi ad literam ("On The Literal Interpretation of Genesis"), he stated that he believed that in some cases new creatures had come about through the "decomposition" of earlier forms of life. For Augustine, "plant, fowl and animal life are not perfect… but created in a state of potentiality", unlike what he considered the theologically perfect forms of
angelAngels are spiritual beings found in many religious traditions. They are broadly viewed as messengers of God, sent to do God's tasks. Traditions vary as to the precise nature and role of these messages and tasks...
s, the
firmamentFirmament is the usual English translation of the Hebrew "raqiya`" meaning an extended solid surface or flat expanse, considered to be a hemisphere above the ground. The word is derived from the Hebrew raqa, meaning "to spread out" by stamping, stretching, beating, or making broad,, e.g...
and the
human soulThe soul, in many religions, spiritual traditions, and philosophies, is the spiritual and eternal part of a living being, commonly held to be separable in existence from the body; distinct from the physical part. It is typically thought to consist of ones consciousness and personality, and can be...
. Augustine's idea 'that forms of life had been transformed "slowly over time"' prompted Father Giuseppe Tanzella-Nitti, Professor of Theology at the
Pontifical Santa Croce UniversityPontifical University of the Holy Cross is a Roman Catholic university under the Curial Congregation for Catholic Education, which it has entrusted to the Prelature of the Holy Cross and Opus Dei, or more commonly called Opus Dei...
in
RomeRome is the capital of Italy and the country's largest and most populated municipality , with over 2.7 million residents in , while the population of the urban area is estimated by Eurostat to be 3.46 million. The metropolitan area of Rome is estimated by OECD to have a population of 3.7 million...
, to claim that Augustine had suggested a form of evolution.
Islamic philosophy and the struggle for existence
Whereas Greek and Roman evolutionary ideas died out in Europe after the fall of the
Roman EmpireThe Roman Empire was the post-Republican phase of the ancient Roman civilization, characterised by an autocratic form of government and large territorial holdings in Europe and around the Mediterranean. The term is used to describe the Roman state during and after the time of the first emperor,...
, they were not lost to
Islamic philosophersIslamic philosophy is a branch of Islamic studies, and is a longstanding attempt to create harmony between philosophy and the religious teachings of Islam .-Definition:...
and scientists. In the
Islamic Golden AgeThe Islamic Golden Age or the Islamic Renaissance, is traditionally dated from the 9th to 13th centuries for 400 years C.E., but has been extended to the 15th century by recent scholarship...
, early ideas on evolution were taught in
Islamic schoolsMadrasah is the Arabic word for any type of educational institution, whether secular or religious...
.
John William DraperJohn William Draper was an American scientist, philosopher, physician, chemist, historian, and photographer.-Early life:...
, the 19th-century scientist, philosopher and historian, discussed the 12th-century writings of
al-KhaziniAbd al-Rahman al-Khazini was a scientist, astronomer, physicist, biologist, alchemist, mathematician and philosopher from Merv, then in the Khorasan province of Persia but now in Turkmenistan, who made important contributions to physics and astronomy. He is considered the greatest scholar from...
as part of what he called the "
MohammedanMohammedan is a term used as both a noun and an adjective meaning belonging or relating to either the religion of Islam or to that of the Islamic prophet Muhammad; a term largely rejected by the Muslim world as a misnomer The term is now largely superseded by Muslim, Moslem or Islamic, but was...
theory of evolution". He compared these early ideas to later biological theories, arguing that the former were developed "... much farther than we are disposed to do, extending them even to inorganic or mineral things".
The first Muslim biologist and philosopher to speculate in detail about evolution was the
Afro-ArabAfro-Arab can refer to people of mixed Black African and genealogical Arab ancestral heritage and/or linguistically and culturally Arabized Black Africans...
writer
al-JahizAl-Jāḥiẓ was a famous Afro-Arab scholar of East African descent, the grandson of a Negro slave...
in the 9th century. He considered the effects of the environment on an animal's chances for survival, and described the struggle for existence.
Ibn MiskawayhAbu 'Ali Ahmad ibn Muhammad ibn Ya'qub Ibn Miskawayh, also known as Ibn Miskawayh was a prominent Persian philosopher, scientist, poet and historian from Ray, Iran. He was active politically during the Buwayhid era....
's
al-Fawz al-Asghar and the
Brethren of PurityThe Brethren of Purity were a mysterious organization, whose identity has never been become clear, Muslim philosophers in Basra, Iraq - which was then the seat of the Abbasid Caliphate - sometime during the 10th century CE.Their esoteric teachings and philosophy are...
's
Encyclopedia of the Brethren of PurityThe Encyclopedia of the Brethren of Purity was a large encyclopedia in 52 treatises written by the mysterious Brethren of Purity of Basra, Iraq sometime in...
(
The Epistles of Ikhwan al-Safa) set forth ideas on how species developed: from matter into vapor and thence to water, then minerals into plants and then animals, leading to apes and, finally, humans. The
polymathA polymath is a person whose expertise fills a significant number of subject areas. In less formal terms, a polymath may simply refer to someone who is very knowledgeable...
Ibn al-Haytham wrote a book in which he argued for
evolutionismEvolutionism refers to doctrines of evolution, specifically to a widely held 19th century belief that organisms are intrinsically bound to improve themselves, and that changes are progressive and arise through inheritance of acquired characters, as in Lamarckism. The belief was extended to include...
(although not natural selection). Numerous other Islamic scholars and scientists, such as Abū Rayhān al-Bīrūnī, Nasir al-Din Tusi, and
Ibn KhaldunIbn Khaldūn or Ibn Khaldoun Ibn Khaldūn or Ibn Khaldoun Ibn Khaldūn or Ibn Khaldoun (full name, , , (May 27, 1332 AD/732 AH – March 19, 1406 AD/808 AH) was a North African polymath — an astronomer, economist, historian, Islamic scholar, Islamic theologian, hafiz, jurist, lawyer,...
discussed and developed these ideas. Translated into Latin, these works began to appear in Europe after the
RenaissanceThe Renaissance was a cultural movement that spanned roughly the 14th to the 17th century, beginning in Florence in the Late Middle Ages and later spreading to the rest of Europe...
and may have had an impact on Western science.
Christian philosophy and the great chain of being
During the
Early Middle AgesThe Early Middle Ages, or Dark Ages, is a period in the history of Europe following the fall of the Western Roman Empire. It lasted from about AD 500 to 1000. The period featured raiding, migration, and conquest by Huns, Germanic peoples, Arabs, Vikings, Hungarians and others. There was frequent...
, Greek classical learning was all but lost to the West. However, contact with the
Islamic worldThe Islamic Golden Age or the Islamic Renaissance, is traditionally dated from the 9th to 13th centuries for 400 years C.E., but has been extended to the 15th century by recent scholarship...
, where Greek manuscripts were preserved and elaborated on, soon led to a massive spate of Latin translations in the 12th century. Europeans were thus re-introduced to the works of Plato and Aristotle, as well as to
Islamic thoughtEarly Islamic philosophy or classical Islamic philosophy is a period of intense philosophical development beginning in the 2nd century AH of the Islamic calendar and lasting until the 6th century AH...
.
Christian thinkersChristian philosophy is a term to describe the fusion of various fields of philosophy with the theological doctrines of Christianity.-Reconciling Christianity with philosophy:...
of the
scholasticScholasticism is derived from the Latin word scholasticus , which means "that [which] belongs to the school," and was a method of learning taught by the academics of medieval universities circa 1100–1500...
school, in particular Abelard and Aquinas, combined Aristotelian classification with Plato's ideas of the goodness of God, and of all potential life forms being present in a perfect creation, to organize all inanimate, animate, and spiritual beings into a huge interconnected system: the
scala naturæ, or
great chain of beingThe scala naturae , is a classical and Western medieval concept of God's strict and natural hierarchical structure of the universe.-Divisions:...
.
Within this system, everything that existed could be placed in order, from "lowest" to "highest", with
HellIn many religious traditions, Hell is a place of suffering and punishment in the afterlife, often in the underworld. Religions with a linear divine history often depict Hell as endless...
at the bottom and God at the top—below God, an angelic hierarchy marked by the orbits of the planets, mankind in an intermediate position, and worms the lowest of the animals. As the universe was ultimately perfect, the great chain was also perfect. There were no empty links in the chain, and no link was represented by more than one species. Therefore no species could ever move from one position to another. Thus, in this Christianized version of Plato's perfect universe, species could never change, but remained forever fixed, in accordance with the text of
Genesis. For humans to forget their position was seen as sinful, whether they behaved like lower animals or aspired to a higher station than was given them by their Creator.
Creatures on adjacent steps were expected to closely resemble each other, an idea expressed in the saying: ("nature does not make leaps"). This basic concept of the great chain of being greatly influenced the thinking of
Western civilizationWestern culture refers to cultures of European origin.The term "Western culture" is used very broadly to refer to a heritage of social norms, ethical values, traditional customs, religious beliefs, political systems, and specific artifacts and technologies...
for centuries (and still has an influence today). It formed a part of the
argument from designA teleological argument, or argument from design, is an argument for the existence of God or a creator based on perceived evidence of order, purpose, design, or direction — or some combination of these — in nature. The word "teleological" is derived from the Greek word telos, meaning "end" or...
presented by
natural theologyNatural theology is a branch of theology based on reason and ordinary experience. Thus it is distinguished from revealed theology which is based on scripture and religious experiences of various kinds; and also from transcendental theology, theology from a priori reasoning.Marcus Terentius Varro ...
. As a classification system, it became the major organizing principle and foundation of the emerging science of
biologyBiology is the natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy...
in the 17th and 18th centuries.
Renaissance and Enlightenment
Some
evolutionistEvolutionism refers to doctrines of evolution, specifically to a widely held 19th century belief that organisms are intrinsically bound to improve themselves, and that changes are progressive and arise through inheritance of acquired characters, as in Lamarckism. The belief was extended to include...
theories explored between 1650 and 1800 postulated that the universe, including life on Earth, had developed mechanically, entirely without divine guidance. Around this time, the
mechanical philosophyIn philosophy, mechanism is the theory that all natural phenomena can be explained by laws of nature. It's the opposite of vitalism, which claims organisms have "vital forces" which aren't physical....
of
René DescartesRené Descartes , , also known as Renatus Cartesius , was a French philosopher, mathematician, physicist, and writer who spent most of his adult life in the Dutch Republic...
began to encourage the metaphor of the universe as a machine that would come to characterise the
scientific revolutionIn the history of science, the scientific revolution was a period when new ideas in physics, astronomy, biology, human anatomy, chemistry, and other sciences led to a rejection of doctrines that had prevailed from Ancient Greece through the Middle Ages, and laid the foundation of modern science...
. However, most contemporary theories of evolution, such of those of
Gottfried LeibnizGottfried Wilhelm Leibniz was a German philosopher, polymath and mathematician who wrote primarily in Latin and French....
and J. G. Herder, held that evolution was a fundamentally
spiritual process. In 1751,
Pierre Louis MaupertuisPierre-Louis Moreau de Maupertuis was a French mathematician, philosopher and man of letters. He became the Director of the Académie des Sciences, and the first President of the Berlin Academy of Science, at the invitation of Frederick the Great.Maupertuis made an expedition to Lapland to...
veered toward more
materialistThe philosophy of materialism holds that the only thing that exists is matter; that all things are composed of material and all phenomena are the result of material interactions. In other words, matter is the only substance. As a theory, materialism is a form of physicalism and belongs to the...
ground. He wrote of natural modifications occurring during reproduction and accumulating over the course of many generations, producing races and even new species, and he anticipated in general terms the idea of natural selection.
Later in the 18th century, the French natural philosopher
G. L. L. BuffonGeorges-Louis Leclerc, Comte de Buffon was a French naturalist, mathematician, cosmologist and encyclopedic author. His collected information influenced the next two generations of naturalists, including Jean-Baptiste Lamarck and Georges Cuvier...
suggested that what most people referred to as species were really just well-marked varieties modified from an original form by environmental factors. For example, he believed that lions, tigers, leopards and house cats might all have a common ancestor. He further speculated that the 200 or so species of mammals then known might have descended from as few as 38 original forms. Buffon’s evolutionary ideas were limited; he believed each of the original forms had arisen through spontaneous generation and that each was shaped by "internal moulds" that limited the amount of change. Buffon was one of the leading 18th century
naturalistNaturalist may refer to:* A scholar or student of natural history, the science of the natural world; see also natural science. It may also refer to a Wildlife enthusiast or a Conservationist....
s and his works
Natural History, and
The Epochs of Nature, which contained well developed theories about a completely materialistic origin for the Earth as well as his ideas questioning the fixity of species, were extremely influential.
Between 1767 and 1792,
James Burnett, Lord MonboddoJames Burnett, Lord Monboddo was a Scottish judge, scholar of linguistic evolution, philosopher and deist. He is most famous today as a founder of modern comparative historical linguistics . In 1767 he became a judge in the Court of Session. As such, Burnett adopted an honorary title based on his...
included in his writings not only the concept that man had descended from primates, but also that, in response to the environment, creatures had found methods of transforming their characteristics over long time intervals. Charles Darwin’s grandfather,
Erasmus DarwinErasmus Darwin was an English physician who turned down the invitation of George III for him to be a Royal Physician. He was also a natural philosopher, physiologist, abolitionist, inventor and poet...
, published
ZoönomiaZoonomia, or the Laws of Organic Life is a two-volume medical work by Erasmus Darwin dealing with pathology, anatomy, psychology, and the functioning of the body...
in 1796, which suggested that "all warm-blooded animals have arisen from one living filament". In his 1802 poem
Temple of Nature, he described the rise of life from minute organisms living in the mud to all of its modern diversity.
Paleontology and geology
In 1796,
Georges CuvierGeorges Léopold Chrétien Frédéric Dagobert Cuvier was a French naturalist and zoologist. Of humble working class origins, he belonged to a new class of self-made scholars who worked their way to the top of academe...
published his findings on the differences between living
elephantElephants are large land mammals in two genera of the family Elephantidae: Elephas and Loxodonta. Three species of elephant are living today: the African Bush Elephant, the African Forest Elephant and the Asian Elephant...
s and those found in the
fossilFossils are the preserved remains or traces of animals, plants, and other organisms from the remote past. The totality of fossils, both discovered and undiscovered, and their placement in fossiliferous rock formations and sedimentary layers is known as the fossil record...
record. His analysis demonstrated that
mammothA mammoth is any species of the extinct genus Mammuthus. These proboscideans are members of Elephantidae, the family of elephants and mammoths, and close relatives of modern elephants. They were often equipped with long curved tusks and, in northern species, a covering of long hair. They lived from...
s and
mastodonMastodons or mastodonts were large tusked mammal species of the extinct genus Mammut found in Asia, Africa, Europe, North America and Central America from the Oligocene through Pleistocene, 33.9 mya to 11,000 years ago. The American mastodon is the most recent and best known species of the group...
s were distinct species different from any living animal, effectively ending a long-running debate over the possibility of the extinction of a species. In 1788,
James HuttonJames Hutton MD was a Scottish geologist, physician, naturalist, chemist and experimental farmer. He is considered the father of modern geology...
described
gradualGradualism is the belief that changes occur, or ought to occur, slowly in the form of gradual steps -Politics and society:...
geological processes operating continuously over
deep timeDeep time is the concept of geologic time first recognized in the 11th century by the Persian geologist and polymath, Avicenna , and the Chinese naturalist and polymath Shen Kuo...
. In the 1790s
William SmithWilliam Smith was an English geologist, credited with creating the first nationwide geological map. He is known as the "Father of English Geology", although recognition was very slow in coming...
began the process of ordering
rock strataIn geology and related fields, a stratum is a layer of rock or soil with internally consistent characteristics that distinguishes it from contiguous layers. Each layer is generally one of a number of parallel layers that lie one upon another, laid down by natural forces. They may extend over...
by examining fossils in the layers while he worked on his geologic map of
EnglandEngland is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west and the North Sea to the east, with the English Channel to the south separating it from continental...
. Independently, in 1811, Georges Cuvier and
Alexandre BrongniartAlexandre Brongniart was a French chemist, mineralogist, and zoologist, who collaborated with Georges Cuvier on a study of the geology of the region around Paris...
published an influential study of the geologic history of the region around Paris, based on the
stratigraphicStratigraphy, a branch of geology, studies rock layers and layering . It is primarily used in the study of sedimentary and layered volcanic rocks....
succession of rock layers. These works helped establish the antiquity of the Earth. Cuvier advocated
catastrophismCatastrophism is the idea that Earth has been affected in the past by sudden, short-lived, violent events, possibly worldwide in scope.The dominant paradigm of modern geology, in contrast, is uniformitarianism , in which slow incremental changes, such as erosion, create the Earth's appearance...
to explain the patterns of extinction and faunal succession revealed by the fossil record.
Knowledge of the fossil record continued to advance rapidly during the first few decades of the 19th century. By the 1840s, the outlines of the
geologic timescaleThe geologic time scale is a chronologic schema relating stratigraphy to time that is used by geologists, paleontologists and other earth scientists to describe the timing and relationships between events that have occurred during the history of the Earth...
were becoming clear, and in 1841
John PhillipsJohn Phillips FRS was an English geologist.- Life and work :Philips was born at Marden in Wiltshire...
named three major eras, based on the predominant fauna of each: the
PaleozoicThe Paleozoic or Palaeozoic Era is the earliest of three geologic eras of the Phanerozoic eon...
, dominated by marine
invertebrateAn invertebrate is an animal without a vertebral column. The group includes 95% of all animal species — all animals except those in the Chordate subphylum Vertebrata ....
s and fish, the
MesozoicThe Mesozoic Era is one of three geologic eras of the Phanerozoic eon. The division of time into eras dates back to Giovanni Arduino, in the 18th century, although his original name for the era now called the "Mesozoic" was "Secondary" The Mesozoic Era is one of three geologic eras of the...
, the age of reptiles, and the current
CenozoicThe Cenozoic Era The Cenozoic (also Cænozoic or Cainozoic) Era The Cenozoic (also Cænozoic or Cainozoic) Era (meaning "new life" (Greek (kainos), "new", and (zoe), "life"), is the most recent of the three classic geological eras and covers the period from 65.5 million years ago to the...
age of mammals. This progressive picture of the history of life was accepted even by conservative English geologists like
Adam SedgwickAdam Sedgwick was one of the founders of modern geology. He proposed the Devonian period of the geological timescale and later the Cambrian period. The latter proposal was based on work which he did on Welsh rock strata...
and
William BucklandThe Very Rev. Dr William Buckland DD FRS was an English geologist, palaeontologist and Dean of Westminster, who wrote the first full account of a fossil dinosaur...
; however, like Cuvier, they attributed the progression to repeated catastrophic episodes of extinction followed by new episodes of creation. Unlike Cuvier, Buckland and some other advocates of
natural theologyNatural theology is a branch of theology based on reason and ordinary experience. Thus it is distinguished from revealed theology which is based on scripture and religious experiences of various kinds; and also from transcendental theology, theology from a priori reasoning.Marcus Terentius Varro ...
among British geologists made efforts to explicitly link the last catastrophic episode proposed by Cuvier to the biblical flood.
From 1830 to 1833,
Charles LyellSir Charles Lyell, 1st Baronet, Kt, FRS was a British lawyer, geologist, and proponent of uniformitarianism. He was the foremost geologist of his day, and an influence on the young Charles Darwin.- Life :...
published his multi-volume work
Principles of GeologyPrinciples of Geology, being an attempt to explain the former changes of the Earth's surface, by reference to causes now in operation, is a book by the Scottish geologist Charles Lyell....
, which, building on Hutton's ideas, advocated a
uniformitarianUniformitarianism, in the philosophy of science, assumes that the same natural laws and processes that operate in the universe now, have always operated in the universe in the past and apply everywhere in the universe...
alternative to the catastrophic theory of geology. Lyell claimed that, rather than being the products of cataclysmic (and possibly supernatural) events, the geologic features of the Earth are better explained as the result of the same gradual geologic forces observable in the present day—but acting over immensely long periods of time. Although Lyell opposed evolutionary ideas (even questioning the consensus that the fossil record demonstrates a true progression), his concept that the Earth was shaped by forces working gradually over an extended period, and the immense age of the Earth assumed by his theories, would strongly influence future evolutionary thinkers such as
Charles DarwinCharles Robert Darwin FRS was an English naturalist who realised and presented compelling evidence that all species of life have evolved over time from common ancestors, through the process he called natural selection...
.
Transmutation of species
Jean-Baptiste LamarckJean-Baptiste Pierre Antoine de Monet, Chevalier de la Marck , often just known as 'Lamarck', was a French soldier, naturalist, academic and an early proponent of the idea that evolution occurred and proceeded in accordance with natural laws.Lamarck fought in the Pomeranian War with Prussia, and...
proposed, in his
Philosophie ZoologiquePhilosophie zoologique ou exposition des considérations relatives à l'histoire naturelle des animaux is an 1809 book by Jean-Baptiste Lamarck in which he outlines his theory of evolution now known as Lamarckism.- External links :* http://www.ucl.ac.uk/taxome/jim/Mim/lamarck_contents.html*...
of 1809, a theory of the transmutation of species. Lamarck did not believe that all living things shared a common ancestor but rather that simple forms of life were created continuously by
spontaneous generationIn the natural sciences, abiogenesis, or "chemical evolution", is the study of how life on Earth could have arisen from inanimate matter. It should not be confused with evolution, which is the study of how groups of living things change over time...
. He also believed that an innate life force drove species to become more complex over time, advancing up a linear ladder of complexity that was related to the great chain of being. Lamarck recognized that species were adapted to their environment. He explained this by saying that the same innate force driving increasing complexity caused the organs of an animal (or a plant) to change based on the use or disuse of those organs, just as muscles are affected by exercise. He argued that these changes would be inherited by the next generation and produce slow adaptation to the environment. It was this secondary mechanism of adaptation through the inheritance of acquired characteristics that would become known as
LamarckismLamarckism is the once popularly accepted, but since mainly discredited, idea that an organism can pass on characteristics that it acquired during its lifetime to its offspring...
and would influence discussions of evolution into the 20th century.
A radical British school of comparative anatomy that included the anatomist
Robert GrantRobert Edmond Grant MD FRCPEd FRS was born in Edinburgh and educated at Edinburgh University as a physician. He became one of the foremost biologists of the early 19th century at Edinburgh and subsequently the first Professor of Comparative Anatomy at University College London...
was closely in touch with Lamarck's French school of
Transformationism. One of the French scientists who influenced Grant was the anatomist
Étienne Geoffroy Saint-HilaireÉtienne Geoffroy Saint-Hilaire was a French naturalist who established the principle of "unity of composition". He was a colleague of Jean-Baptiste Lamarck and expanded and defended Lamarck's evolutionary theories...
, whose ideas on the unity of various animal body plans and the
homologyIn evolutionary biology, homology refers to any similarity between characteristics of organisms that is due to their shared ancestry. The word homologous derives from the ancient Greek ομολογειν, 'to agree'. There are examples in different branches of biology...
of certain anatomical structures would be widely influential and lead to intense debate with his colleague
Georges CuvierGeorges Léopold Chrétien Frédéric Dagobert Cuvier was a French naturalist and zoologist. Of humble working class origins, he belonged to a new class of self-made scholars who worked their way to the top of academe...
. Grant became an authority on the anatomy and reproduction of marine invertebrates. He developed Lamarck's and
Erasmus DarwinErasmus Darwin was an English physician who turned down the invitation of George III for him to be a Royal Physician. He was also a natural philosopher, physiologist, abolitionist, inventor and poet...
's ideas of
transmutationTransmutation of species was a term used by Jean Baptiste Lamarck in 1809 for his theory that described the altering of one species into another. It was one of the names commonly used for evolutionary ideas in the 19th century before Charles Darwin published On The Origin of Species...
and
evolutionismEvolutionism refers to doctrines of evolution, specifically to a widely held 19th century belief that organisms are intrinsically bound to improve themselves, and that changes are progressive and arise through inheritance of acquired characters, as in Lamarckism. The belief was extended to include...
, and investigated homology to prove
common descentA group of organisms is said to have common descent if they have a common ancestor. In modern biology, it is generally accepted that all living organisms on Earth are descended from a common ancestor or ancestral gene pool....
. As a young student Charles Darwin joined Grant in investigations of the life cycle of marine animals. In 1826 an anonymous paper, probably written by
Robert Jamesonthumb|Robert JamesonProfessor Robert Jameson was a Scottish naturalist and mineralogist, born in Leith, near Edinburgh, in July 1774. As Regius Professor at the University of Edinburgh for fifty years, Jameson is notable for his advanced scholarship in natural history, his superb museum...
, praised Lamarck for explaining how higher animals had “evolved” from the simplest worms; this was the first use of the word “evolved” in a modern sense.
In 1844, the Scottish publisher
Robert ChambersRobert Chambers was a Scottish author, journal editor and publisher who, like his elder brother William Chambers, the publisher and politician, was highly influential in the mid-19th century in both scientific and political circles...
anonymously published an extremely controversial but widely read book entitled
Vestiges of the Natural History of CreationVestiges of the Natural History of Creation was a significant work of natural history published anonymously in England in 1844. It brought together various ideas of stellar evolution and progressive transmutation of species governed by God-given laws in an accessible narrative which tied together...
. This book proposed an evolutionary scenario for the origins of the Solar System and life on Earth. It claimed that the fossil record showed a progressive ascent of animals with current animals being branches off a main line that leads progressively to humanity. It implied that the transmutations lead to the unfolding of a preordained plan that had been woven into the laws that governed the universe. In this sense it was less completely materialistic than the ideas of radicals like Robert Grant, but its implication that humans were only the last step in the ascent of animal life incensed many conservative thinkers. The high profile of the public debate over
Vestiges, with its depiction of evolution as a progressive process, would greatly influence the perception of Darwin's theory a decade later.
Ideas about the transmutation of species were associated with the radical materialism of the
EnlightenmentThe Age of Enlightenment, or simply The Enlightenment, is a term used to describe a time in Western philosophy and cultural life, centered upon the eighteenth century, in which reason was advocated as the primary source and legitimacy for authority....
and were attacked by more conservative thinkers.
Georges CuvierGeorges Léopold Chrétien Frédéric Dagobert Cuvier was a French naturalist and zoologist. Of humble working class origins, he belonged to a new class of self-made scholars who worked their way to the top of academe...
attacked the ideas of Lamarck and Geoffroy Saint-Hilaire, agreeing with Aristotle that species were immutable. Cuvier believed that the individual parts of an animal were too closely correlated with one another to allow for one part of the anatomy to change in isolation from the others, and argued that the fossil record showed patterns of catastrophic extinctions followed by re-population, rather than gradual change over time. He also noted that drawings of animals and animal mummies from Egypt, which were thousands of years old, showed no signs of change when compared with modern animals. The strength of Cuvier's arguments and his scientific reputation helped keep transmutational ideas out of the mainstream for decades.
In Britain the philosophy of
natural theologyNatural theology is a branch of theology based on reason and ordinary experience. Thus it is distinguished from revealed theology which is based on scripture and religious experiences of various kinds; and also from transcendental theology, theology from a priori reasoning.Marcus Terentius Varro ...
remained influential.
William PaleyWilliam Paley was a British Christian apologist, philosopher, and utilitarian. He is best known for his exposition of the teleological argument for the existence of God in his work Natural Theology, which made use of the watchmaker analogy .-Life:Born in Peterborough, England, Paley was educated...
's 1802 book
Natural Theology with its famous
watchmaker analogyThe watchmaker analogy, or watchmaker argument, is a teleological argument for the existence of God. By way of an analogy, the argument states that design implies a designer...
had been written at least in part as a response to the transmutational ideas of
Erasmus DarwinErasmus Darwin was an English physician who turned down the invitation of George III for him to be a Royal Physician. He was also a natural philosopher, physiologist, abolitionist, inventor and poet...
. Geologists influenced by natural theology, such as Buckland and Sedgwick, made a regular practice of attacking the evolutionary ideas of Lamarck, Grant, and
The Vestiges of the Natural History of Creation. Although the geologist
Charles LyellSir Charles Lyell, 1st Baronet, Kt, FRS was a British lawyer, geologist, and proponent of uniformitarianism. He was the foremost geologist of his day, and an influence on the young Charles Darwin.- Life :...
opposed scriptural geology, he also believed in the immutability of species, and in his
Principles of Geology (1830–1833), he criticized Lamarck's theories of development. Idealists such as
Louis AgassizJean Louis Rodolphe Agassiz was a paleontologist, glaciologist, and geologist, and was a prominent innovator in the study of the Earth's natural history. He grew up in Switzerland and became a professor of natural history at University of Neuchâtel...
and
Richard OwenSir Richard Owen KCB was an English biologist, comparative anatomist and palaeontologist.Owen is probably best remembered today for coining the word Dinosauria and for his outspoken opposition to Charles Darwin's theory of evolution by natural selection...
believed that each species was fixed and unchangeable because it represented an idea in the mind of the creator. They believed that relationships between species could be discerned from developmental patterns in
embryologyEmbryology is the study of the development of an embryo. An embryo is defined as any organism in an early stage well before birth or hatching, or in plants, before germination occurs....
, as well as in the fossil record, but that these relationships represented an underlying pattern of divine thought, with progressive creation leading to increasing complexity and culminating in humanity. Owen developed the idea of "archetypes" in the Divine mind that would produce a sequence of species related by anatomical
homologiesIn evolutionary biology, homology refers to any similarity between characteristics of organisms that is due to their shared ancestry. The word homologous derives from the ancient Greek ομολογειν, 'to agree'. There are examples in different branches of biology...
, such as
vertebrateVertebrates are members of the subphylum Vertebrata, chordates with backbones or spinal columns. About 58,000 species of vertebrates have been described. Vertebrata is the largest subphylum of chordates, and contains many familiar groups of large land animals. Vertebrates comprise cyclostomes, bony...
limbs. Owen led a public campaign that successfully marginalized Robert Grant in the scientific community. Darwin would make good use of the homologies analyzed by Owen in his own theory, but the harsh treatment of Grant, and the controversy surrounding
Vestiges, would contribute to his decision to delay publishing his ideas.
Anticipations of natural selection
Several writers anticipated aspects of Darwin's theory, and in the third edition of
On the Origin of Species published in 1861 Darwin named those he knew about in an introductory appendix,
An Historical Sketch of the Recent Progress of Opinion on the Origin of Species, which he expanded in later editions.
In 1813,
William Charles WellsWilliam Charles Wells MD FRS FRSEd , was a Scottish-American physician and printer. He lived a life of extraordinary variety, did some notable medical research, and made the first clear statement about natural selection. He applied the idea to the origin of different skin colours in human races,...
read before the
Royal SocietyThe Royal Society of London for the Improvement of Natural Knowledge, known simply as the Royal Society, or even the Royal, is a learned society for science that was founded in 1660 and is considered by most to be the oldest such society still in existence...
essays assuming that there had been evolution of humans, and recognising the principle of
natural selectionNatural selection is the process by which heritable traits that make it more likely for an organism to survive and successfully reproduce become more common in a population over successive generations...
. Charles Darwin and Alfred Russel Wallace were unaware of this work when they jointly published the theory in 1858, but Darwin later acknowledged that Wells had recognised the principle before them, writing that the paper "An Account of a White Female, part of whose Skin resembles that of a Negro" was published in 1818, and "he distinctly recognises the principle of natural selection, and this is the first recognition which has been indicated; but he applies it only to the races of man, and to certain characters alone." When Darwin was developing his theory, he was influenced by
Augustin de CandolleAugustin Pyramus de Candolle also spelt Augustin Pyrame de Candolle was a botanist. The author abbreviation used in citing plant names he published is "DC."....
's
natural system of classification, which laid emphasis on the war between competing species.
Patrick MatthewPatrick Matthew was a Scottish landowner and fruit farmer. He published the principle of natural selection as a mechanism of evolution over a quarter-century earlier than Charles Darwin and Alfred Russel Wallace...
wrote in the obscure book
Naval Timber & Arboriculture (1831) of "continual balancing of life to circumstance. ... [The] progeny of the same parents, under great differences of circumstance, might, in several generations, even become distinct species, incapable of co-reproduction." Charles Darwin discovered this work after the initial publication of the
Origin. In the brief historical sketch that Darwin included in the 3rd edition he says "Unfortunately the view was given by Mr. Matthew very briefly in an Appendix to a work on a different subject ... He clearly saw, however, the full force of the principle of natural selection."
It is possible to look through the history of biology from the ancient Greeks onwards and discover anticipations of almost all of Darwin's key ideas. However, as historian of science
Peter J. BowlerPeter J. Bowler is a historian of biology who has written extensively on the history of evolutionary thought, the history of the environmental sciences, and on the history of genetics. His 1984 book, Evolution: The History of an Idea is a standard textbook on the history of evolution, and was...
says, "Through a combination of bold theorizing and comprehensive evaluation, Darwin came up with a concept of evolution that was unique for the time." Bowler goes on to say that simple priority alone is not enough to secure a place in the history of science; someone has to develop an idea and convince others of its importance to have a real impact.
T. H. Huxley said in his essay on the reception of the
Origin of Species:
The suggestion that new species may result from the selective action of external conditions upon the variations from their specific type which individuals present and which we call spontaneous because we are ignorant of their causation is as wholly unknown to the historian of scientific ideas as it was to biological specialists before 1858. But that suggestion is the central idea of the Origin of Species, and contains the quintessence of DarwinismDarwinism is a term used for various movements or concepts related to ideas of transmutation of species or evolution, including ideas with no connection to the work of Charles Darwin. The meaning of Darwinism has changed over time, and varies depending on who is using the term...
.
Natural selection
The
biogeographicalBiogeography is the study of the distribution of biodiversity over space and time. It aims to reveal where organisms live, and at what abundance....
patterns Charles Darwin observed in places such as the
Galapagos islandsThe Galápagos Islands are an archipelago of volcanic islands distributed around the equator in the Pacific Ocean, 972 km west of continental Ecuador...
during
the voyage of the BeagleThe second voyage of HMS Beagle from 27 December 1831 to 2 October 1836 was the second survey expedition of HMS Beagle, under captain Robert FitzRoy who had taken over command of the ship on its first voyage after her previous captain committed suicide...
caused him to doubt the fixity of species, and in 1837 Darwin started the first of a series of secret notebooks on
transmutationTransmutation of species was a term used by Jean Baptiste Lamarck in 1809 for his theory that described the altering of one species into another. It was one of the names commonly used for evolutionary ideas in the 19th century before Charles Darwin published On The Origin of Species...
. Darwin's observations led him to view transmutation as a process of divergence and branching, rather than the ladder-like progression envisioned by Lamarck and others. In 1838 he read the new 6th edition of
An Essay on the Principle of PopulationThe book An Essay on the Principle of Population was first published anonymously in 1798 through J. Johnson .The author was soon identified as The Reverend Thomas Robert Malthus....
, written in the late 1700s by
Thomas MalthusDr. Thomas Robert Malthus FRS ,was a Jewish scholar, influential in political economy and demography. Malthus popularised the economic theory of rent....
. Malthus' idea of population growth leading to a struggle for survival combined with Darwin's knowledge on how breeders selected traits, led to the
inception of Darwin's theoryThe inception of Darwin's theory occurred during an intensively busy period which began when Charles Darwin returned from the survey voyage of the Beagle, with his reputation as a fossil collector and geologist already established...
of
natural selectionNatural selection is the process by which heritable traits that make it more likely for an organism to survive and successfully reproduce become more common in a population over successive generations...
. Darwin did not publish his ideas on evolution for 20 years. However he did share them with certain other naturalists and friends, starting with
Joseph HookerSir Joseph Dalton Hooker OM, GCSI, CB, MD, FRS was one of the greatest British botanists and explorers of the 19th century. Hooker was one of the founders of geographical botany, and Charles Darwin's closest friend...
, with whom he discussed his unpublished 1844 essay on natural selection. During this period he used the time he could spare from his other scientific work to slowly refine his ideas and, aware of the intense controversy around transmutation, amass evidence to support them.
Unlike Darwin,
Alfred Russel WallaceAlfred Russel Wallace, OM, FRS was a British naturalist, explorer, geographer, anthropologist and biologist...
, influenced by the book
Vestiges of the Natural History of CreationVestiges of the Natural History of Creation was a significant work of natural history published anonymously in England in 1844. It brought together various ideas of stellar evolution and progressive transmutation of species governed by God-given laws in an accessible narrative which tied together...
, already suspected that transmutation of species occurred when he began his career as a naturalist. By 1855 his biogeographical observations during his field work in
South AmericaSouth America is the southern continent of the Americas, situated entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere...
and the
Malay ArchipelagoThe Malay Archipelago and Maritime Southeast Asia are names given to the archipelago located between mainland Southeastern Asia and Australia. Located between the Indian and Pacific Oceans, the group of 20,000 islands is the world's largest archipelago by area...
made him confident enough in a branching pattern of evolution to publish a paper stating that every species originated in close proximity to an already existing closely allied species. Like Darwin, it was Wallace's consideration of how the ideas of Malthus might apply to animal populations that led him to conclusions very similar to those reached by Darwin about the role of natural selection. In February 1858 Wallace, unaware of Darwin's unpublished ideas, composed his thoughts into an essay and mailed them to Darwin, asking for his opinion. The result was the joint publication in July of an extract from Darwin's 1844 essay along with Wallace's letter. Darwin also began work in earnest on
The Origin of Species, which he would publish in 1859.
1859–1930s: Darwin and his legacy
By the 1850s whether or not species evolved was a subject of intense debate, with prominent scientists arguing both sides of the issue. However, it was the publication of
Charles DarwinCharles Robert Darwin FRS was an English naturalist who realised and presented compelling evidence that all species of life have evolved over time from common ancestors, through the process he called natural selection...
's
On the Origin of Species (1859) that fundamentally transformed the discussion over biological origins. Darwin argued that his branching version of evolution explained a wealth of facts in biogeography, anatomy, embryology, and other fields of biology. He also provided the first cogent mechanism by which evolutionary change could persist: his theory of natural selection.
One of the first and most important naturalists to be convinced by
Origin of the reality of evolution was the British anatomist Thomas Henry Huxley. Huxley recognized that unlike the earlier transmutational ideas of Lamarck and
Vestiges, Darwin's theory provided a mechanism for evolution without supernatural involvement, even if Huxley himself was not completely convinced that
natural selectionNatural selection is the process by which heritable traits that make it more likely for an organism to survive and successfully reproduce become more common in a population over successive generations...
was the key evolutionary mechanism. Huxley would make advocacy of evolution a cornerstone of the program of the
X ClubThe X Club was a dining club of nine men who supported the theories of natural selection and academic liberalism in late 19th-century England. Thomas Henry Huxley was the initiator: he called the first meeting for November 3, 1864...
to reform and professionalise science by displacing
natural theologyNatural theology is a branch of theology based on reason and ordinary experience. Thus it is distinguished from revealed theology which is based on scripture and religious experiences of various kinds; and also from transcendental theology, theology from a priori reasoning.Marcus Terentius Varro ...
with
naturalismNaturalism is divided into two philosophical stances:*Naturalized epistemology which focuses on epistemology: This stance is concerned with knowledge: what are methods for gaining trustworthy knowledge of the natural world? It is an epistemological view that is specifically concerned with practical...
and to end the domination of British natural science by the clergy. By the early 1870s in English-speaking countries, thanks partly to these efforts, evolution had become the mainstream scientific explanation for the origin of species. In his campaign for public and scientific acceptance of Darwin's theory, Huxley made extensive use of new evidence for evolution from paleontology. This included evidence that birds had evolved from reptiles, including the discovery of
ArchaeopteryxArchaeopteryx, sometimes referred to by its German name Urvogel , is the earliest and most primitive bird known...
in Europe, and a number of fossils of primitive birds with teeth found in North America. Another important line of evidence was the finding of fossils that helped trace the
evolution of the horseThe evolution of the horse involves the gradual development of the modern horse from the fox-sized, forest-dwelling Hyracotherium. Paleozoologists have been able to piece together a more complete picture of the modern horse's evolutionary lineage than that of any other animal.The horse belongs to...
from its small five-toed ancestors. However, acceptance of evolution among scientists in non-English speaking nations such as France, and the countries of southern Europe and Latin America was slower. An exception to this was Germany, where both
August WeismannFriedrich Leopold August Weismann was a German evolutionary biologist. Ernst Mayr ranked him the second most notable evolutionary theorist of the 19th century, after Charles Darwin....
and
Ernst HaeckelErnst Heinrich Philipp August Haeckel ,also written von Haeckel, was an eminent German biologist, naturalist, philosopher, physician, professor and artist who discovered, described and named thousands of new species, mapped a genealogical tree relating all life forms, and coined many terms in...
championed this idea: Haeckel used evolution to challenge the established tradition of metaphysical idealism in German biology, much as Huxley used it to challenge natural theology in Britain. Haeckel and other German scientists would take the lead in launching an ambitious programme to reconstruct the evolutionary history of life based on
morphology (biology)In biology morphology is the form, structure and configuration of an organism.This includes aspects of the outward appearance as well as the form and structure of the internal parts like bones and organs...
and
embryologyEmbryology is the study of the development of an embryo. An embryo is defined as any organism in an early stage well before birth or hatching, or in plants, before germination occurs....
.
Darwin's theory succeeded in profoundly altering scientific opinion regarding the development of life and in producing a small philosophical revolution. However, this theory could not explain several critical components of the evolutionary process. Specifically, Darwin was unable to explain the source of variation in traits within a species, and could not identify a mechanism that could pass traits faithfully from one generation to the next. Darwin's hypothesis of
pangenesisPangenesis was Charles Darwin's hypothetical mechanism for heredity. He presented this 'provisional hypothesis' in his 1868 work The Variation of Animals and Plants under Domestication and felt that it brought 'together a multitude of facts which are at present left disconnected by any efficient...
, while relying in part on the inheritance of
acquired characteristicsThe inheritance of acquired traits is a hypothesis about a mechanism of heredity by which changes in physiology acquired over the life of an organism may purportedly be transmitted to offspring...
, proved to be useful for statistical models of evolution that were developed by his cousin
Francis GaltonSir Francis Galton FRS , cousin of Sir Douglas Galton, was an English Victorian polymath, anthropologist, eugenicist, tropical explorer, geographer, inventor, meteorologist, proto-geneticist, psychometrician, and statistician. He was knighted in 1909.Galton had a prolific intellect, and produced...
and the "biometric" school of evolutionary thought. However, this idea proved to be of little use to other biologists.
Application to humans
Charles Darwin was aware of the severe reaction in some parts of the scientific community against the suggestion made in
Vestiges of the Natural History of Creation that humans had arisen from animals by a process of transmutation. Therefore he almost completely ignored the topic of
human evolutionHuman evolution, or anthropogenesis, is the origin and evolution of Homo sapiens as a distinct species from other hominids, great apes and placental mammals...
in
The Origin of Species. Despite this precaution, the issue featured prominently in the debate that followed the book's publication. For most of the first half of the 19th century, the scientific community believed that, although geology had shown that the Earth and life were very old, human beings had appeared suddenly just a few thousand years before the present. However, a series of archaeological discoveries in the 1840s and 1850s showed stone tools associated with the remains of extinct animals. By the early 1860s, as summarized in
Charles LyellSir Charles Lyell, 1st Baronet, Kt, FRS was a British lawyer, geologist, and proponent of uniformitarianism. He was the foremost geologist of his day, and an influence on the young Charles Darwin.- Life :...
's 1863 book
Geological Evidences of the Antiquity of Man, it had become widely accepted that humans had existed during a prehistoric period – which stretched many thousands of years before the start of written history. This view of human history was more compatible with an evolutionary origin for humanity than was the older view. On the other hand, at that time there was no fossil evidence to demonstrate human evolution. The only human fossils found before the discovery of
Java manJava Man is the name given to fossils discovered in 1891 at Trinil - Ngawi Regency on the banks of the Solo River in East Java, Indonesia, one of the first known specimens of Homo erectus...
in the 1890s were either of anatomically modern humans or of
NeanderthalThe Neanderthal , or ), also spelled Neandertal, is an extinct member of the Homo genus that is known from Pleistocene specimens found in Europe and parts of western and central Asia. Neanderthals are either classified as a subspecies of humans or as a separate species...
s that were too close, especially in the critical characteristic of cranial capacity, to modern humans for them to be convincing intermediates between humans and other primates.
Therefore the debate that immediately followed the publication of
The Origin of Species centered on the similarities and differences between humans and modern
apeAn ape is any member of the Hominoidea superfamily of primates. Due to its ambiguous nature, the term ape is less suitable as a means of describing taxonomic relationships....
s. Carolus Linnaeus had been criticised in the 18th century for grouping humans and apes together as primates in his ground breaking classification system.
Richard OwenSir Richard Owen KCB was an English biologist, comparative anatomist and palaeontologist.Owen is probably best remembered today for coining the word Dinosauria and for his outspoken opposition to Charles Darwin's theory of evolution by natural selection...
vigorously defended the classification suggested by Cuvier and
Johann Friedrich BlumenbachJohann Friedrich Blumenbach was a German physician, physiologist and anthropologist, one of the first to explore the study of mankind as an aspect of natural history, whose teachings in comparative anatomy were applied to classification of human races, of which he determined...
that placed humans in a separate order from any of the other mammals, which by the early 19th century had become the orthodox view. On the other hand, Thomas Henry Huxley sought to demonstrate a close anatomical relationship between humans and apes. In one famous incident, Huxley showed that Owen was mistaken in claiming that the brains of
gorillaGorillas are the largest of the living primates. They are ground-dwelling and predominantly herbivorous. They inhabit the forests of central Africa. Gorillas are divided into two species and either four or five subspecies...
s lacked a structure present in human brains. Huxley summarized his argument in his highly influential 1863 book
Evidence as to Man's Place in NatureEvidence as to Man's Place in Nature is a 1863 book by Thomas Henry Huxley, in which he gives evidence for the evolution of man and apes from a common ancestor. It was the first book devoted to the topic of human evolution, and discussed much of the anatomical and other evidence...
. Another viewpoint was advocated by Charles Lyell and
Alfred Russel WallaceAlfred Russel Wallace, OM, FRS was a British naturalist, explorer, geographer, anthropologist and biologist...
. They agreed that humans shared a common ancestor with apes, but questioned whether any purely materialistic mechanism could account for all the differences between humans and apes, especially some aspects of the human mind.
In 1871, Darwin published
The Descent of Man, and Selection in Relation to SexThe Descent of Man, and Selection in Relation to Sex is a book on evolutionary theory by English naturalist Charles Darwin, first published in 1871. It was Darwin's second great book on evolutionary theory, following his 1859 work, On The Origin of Species...
, which contained his views on human evolution. Darwin argued that the differences between the human mind and the minds of the higher animals were a matter of degree rather than of kind. For example, he viewed morality as a natural outgrowth of instincts that were beneficial to animals living in social groups. He argued that all the differences between humans and apes were explained by a combination of the selective pressures that came from our ancestors moving from the trees to the plains, and
sexual selectionSexual selection is the theory proposed by Charles Darwin that states that certain evolutionary traits can be explained by intraspecific competition. Darwin defined sexual selection as the effects of the "struggle between the individuals of one sex, generally the males, for the possession of the...
. The debate over human origins, and over the degree of human uniqueness continued well into the 20th century.
Alternatives to natural selection
Evolution was widely accepted in scientific circles within a few years of the publication of
Origin, but the acceptance of
natural selectionNatural selection is the process by which heritable traits that make it more likely for an organism to survive and successfully reproduce become more common in a population over successive generations...
as its driving mechanism was much less widespread. The four major alternatives to natural selection in the late 19th century were
theistic evolutionTheistic evolution and evolutionary creationism are similar concepts that assert that classical religious teachings about God are compatible with the modern scientific understanding about biological evolution....
,
neo-LamarckismLamarckism is the once popularly accepted, but since mainly discredited, idea that an organism can pass on characteristics that it acquired during its lifetime to its offspring...
,
orthogenesisOrthogenesis, orthogenetic evolution, progressive evolution or autogenesis, is the hypothesis that life has an innate tendency to move in a unilinear fashion due to some internal or external "driving force". The hypothesis is based on essentialism and cosmic teleology and proposes an intrinsic...
, and
saltationismIn biology, saltation is a sudden change from one generation to the next, that is large, or very large, in comparison with the usual variation of an organism...
. Theistic evolution (a term promoted by Darwin's greatest American advocate
Asa GrayAsa Gray is considered the most important American botanist of the 19th century.He was instrumental in unifying the taxonomic knowledge of the plants of North America...
) was the idea that God intervened in the process of evolution to guide it in such a way that the living world could still be considered to be designed. However, this idea gradually fell out of favor among scientists, as they became more and more committed to the idea of
methodological naturalismNaturalism is divided into two philosophical stances:*Naturalized epistemology which focuses on epistemology: This stance is concerned with knowledge: what are methods for gaining trustworthy knowledge of the natural world? It is an epistemological view that is specifically concerned with practical...
and came to believe that direct appeals to supernatural involvement were scientifically unproductive. By 1900, theistic evolution had largely disappeared from professional scientific discussions, although it retained a strong popular following.
In the late 19th century, the term
neo-LamarckismLamarckism is the once popularly accepted, but since mainly discredited, idea that an organism can pass on characteristics that it acquired during its lifetime to its offspring...
came to be associated with the position of naturalists who viewed the inheritance of acquired characteristics as the most important evolutionary mechanism. Advocates of this position included the British writer and Darwin critic
Samuel ButlerSamuel Butler was an iconoclastic Victorian author who published a variety of works, including the Utopian satire Erewhon and the posthumous novel The Way of All Flesh, his two best-known works, but also extending to examinations of Christian orthodoxy, substantive studies of evolutionary thought,...
, the German biologist
Ernst HaeckelErnst Heinrich Philipp August Haeckel ,also written von Haeckel, was an eminent German biologist, naturalist, philosopher, physician, professor and artist who discovered, described and named thousands of new species, mapped a genealogical tree relating all life forms, and coined many terms in...
, and the American paleontologist
Edward Drinker CopeEdward Drinker Cope was an American paleontologist and comparative anatomist, as well as a noted herpetologist and ichthyologist. Born to a wealthy Quaker family, Cope quickly distinguished himself as a child prodigy interested in science; he published his first scientific paper at the age of...
. They considered Lamarckism to be philosophically superior to Darwin's idea of selection acting on random variation. Cope looked for, and thought he found, patterns of linear progression in the fossil record. Inheritance of acquired characteristics was part of Haeckel's
recapitulation theoryThe theory of recapitulation, also called the biogenetic law or embryological parallelism and often expressed as "ontogeny recapitulates phylogeny" is a discredited biological hypothesis...
of evolution, which held that the embryological development of an organism repeats its evolutionary history. Critics of neo-Lamarckism, such as the German biologist
August WeismannFriedrich Leopold August Weismann was a German evolutionary biologist. Ernst Mayr ranked him the second most notable evolutionary theorist of the 19th century, after Charles Darwin....
and
Alfred Russel WallaceAlfred Russel Wallace, OM, FRS was a British naturalist, explorer, geographer, anthropologist and biologist...
, pointed out that no one had ever produced solid evidence for the inheritance of acquired characteristics. Despite these criticisms, neo-Lamarckism remained the most popular alternative to natural selection at the end of the 19th century, and would remain the position of some naturalists well into the 20th century.
Orthogenesis was the
hypothesisA hypothesis is a proposed explanation for an observable phenomenon. The term derives from the Greek, ὑποτιθέναι - hypotithenai meaning "to put under" or "to suppose." For a hypothesis to be put forward as a scientific hypothesis, the scientific method requires that one can test it...
that life has an innate tendency to change, in a unilinear fashion, towards ever-greater perfection. It had a significant following in the 19th century, and its proponents included the Russian biologist Leo Berg and the American paleontologist
Henry Fairfield OsbornHenry Fairfield Osborn was an American geologist, paleontologist, and eugenicist, "a first-rate science administrator and a third-rate scientist."...
. Orthogenesis was popular among some paleontologists, who believed that the fossil record showed a gradual and constant unidirectional change. Saltationism was the idea that new species arise as a result of large mutations. It was seen as a much faster alternative to the Darwinian concept of a gradual process of small random variations being acted on by natural selection, and was popular with early geneticists such as
Hugo de VriesHugo Marie de Vries was a Dutch botanist and one of the first geneticists. He is known chiefly for suggesting the concept of genes, rediscovering the laws of heredity in the 1890s while unaware of Gregor Mendel's work, for introducing the term "mutation", and for developing a mutation theory of...
,
William BatesonWilliam Bateson was a British geneticist, a Fellow of St. John's College, Cambridge...
, and early in his career,
T. H. MorganThomas Hunt Morgan was an American geneticist and embryologist. Morgan received his PhD from Johns Hopkins University in 1890 and researched embryology during his tenure at Bryn Mawr. Following the rediscovery of Mendelian inheritance in 1900, Morgan's research moved to the study of mutation in...
. It became the basis of the
mutation theoryMutationism refers to the theory emphasizing mutation as a creative principle and source of discontinuity in evolutionary change, particularly associated with the founders of modern genetics....
of evolution.
Mendelian genetics, biometrics, and mutation
The so-called rediscovery of
Gregor MendelGregor Johann Mendel was an Augustinian priest and scientist, and is often called the father of genetics for his study of the inheritance of certain traits in pea plants. Mendel showed that the inheritance of these traits follows particular laws, which were later named after him...
's laws of inheritance in 1900 ignited a fierce debate between two camps of biologists. In one camp were the
MendelianMendelian inheritance is a set of primary tenets relating to the transmission of hereditary characteristics from parent organisms to their children; it underlies much of genetics. They were initially derived from the work of Gregor Mendel published in 1865 and 1866 which was "re-discovered" in...
s, who were focused on discrete variations and the laws of inheritance. They were led by
William BatesonWilliam Bateson was a British geneticist, a Fellow of St. John's College, Cambridge...
(who coined the word
geneticsGenetics, , a discipline of biology, is the science of heredity and variation in living organisms. The fact that living things inherit traits from their parents has been used since prehistoric times to improve crop plants and animals through selective breeding...
) and
Hugo de VriesHugo Marie de Vries was a Dutch botanist and one of the first geneticists. He is known chiefly for suggesting the concept of genes, rediscovering the laws of heredity in the 1890s while unaware of Gregor Mendel's work, for introducing the term "mutation", and for developing a mutation theory of...
(who coined the word
mutationIn biology, a mutation is a randomly derived change to the nucleotide sequence of the genetic material of an organism.Mutations can be caused by copying errors in the genetic material during cell division, or by exposure to mutagens , or can be induced by the organism itself, by cellular processes...
). Their opponents were the
biometriciansBiostatistics is the application of statistics to a wide range of topics in biology...
, who were interested in the continuous variation of characteristics within populations. Their leaders,
Karl PearsonKarl Pearson FRS established the disciplineof mathematical statistics.In 1911 he founded the world's first university statistics department at University College London...
and
Walter Frank Raphael WeldonWalter Frank Raphael Weldon DSc FRS generally called Raphael Weldon, was an English evolutionary biologist and a founder of biometry...
, followed in the tradition of
Francis GaltonSir Francis Galton FRS , cousin of Sir Douglas Galton, was an English Victorian polymath, anthropologist, eugenicist, tropical explorer, geographer, inventor, meteorologist, proto-geneticist, psychometrician, and statistician. He was knighted in 1909.Galton had a prolific intellect, and produced...
, who had focused on measurement and
statisticalStatistics is a branch of mathematics concerned with collecting and interpreting data. According to other definitions, it is a mathematical science pertaining to the collection, analysis, interpretation or explanation, and presentation of data. Statisticians improve the quality of data with the...
analysis of variation within a population. The biometricians rejected Mendelian genetics on the basis that discrete units of heredity, such as genes, could not explain the continuous range of variation seen in real populations. Weldon's work with crabs and snails provided evidence that selection pressure from the environment could shift the range of variation in wild populations, but the Mendelians maintained that the variations measured by biometricians were too insignificant to account for the evolution of new species.
When
T. H. MorganThomas Hunt Morgan was an American geneticist and embryologist. Morgan received his PhD from Johns Hopkins University in 1890 and researched embryology during his tenure at Bryn Mawr. Following the rediscovery of Mendelian inheritance in 1900, Morgan's research moved to the study of mutation in...
began experimenting with breeding the fruit fly
Drosophila melanogasterDrosophila melanogaster is a species of Diptera, or the order of flies, in the family Drosophilidae. The species is commonly known as the common fruit fly or vinegar fly. Starting from Charles W...
, he was a saltationist who hoped to demonstrate that a new species could be created in the lab by mutation alone. Instead, the work at his lab between 1910 and 1915 reconfirmed Mendelian genetics and provided solid experimental evidence linking it to chromosomal inheritance. His work also demonstrated that most mutations had relatively small effects, such as a change in eye color, and that rather than creating a new species in a single step, mutations served to increase variation within the existing population.
1920s–1940s
Population genetics
The Mendelian and biometrician models were eventually reconciled with the development of
population geneticsPopulation genetics is the study of the allele frequency distribution and change under the influence of the four evolutionary processes: natural selection, genetic drift, mutation and gene flow. It also takes account of population subdivision and population structure in space. As such, it attempts...
. A key step was the work of the British biologist and statistician
R.A. FisherSir Ronald Aylmer Fisher, FRS was an English statistician, evolutionary biologist, eugenicist and geneticist. He was described by Anders Hald as "a genius who almost single-handedly created the foundations for modern statistical science," and Richard Dawkins described him as "the greatest of...
. In a series of papers starting in 1918 and culminating in his 1930 book
The Genetical Theory of Natural SelectionThe Genetical Theory of Natural Selection is a book by R.A. Fisher first published in 1930 by Clarendon. It is one of the most important books of the modern evolutionary synthesis and is commonly cited in biology books.-Editions:...
, Fisher showed that the continuous variation measured by the biometricians could be produced by the combined action of many discrete genes, and that
natural selectionNatural selection is the process by which heritable traits that make it more likely for an organism to survive and successfully reproduce become more common in a population over successive generations...
could change
gene frequenciesAllele frequency is the proportion of all copies of a gene that is made up of a particular gene variant . In other words, it is the number of copies of a particular allele divided by the number of copies of all alleles at the genetic place in a population. It can be expressed for example as a...
in a population, resulting in evolution. In a series of papers beginning in 1924, another British geneticist,
J.B.S. HaldaneJohn Burdon Sanderson Haldane FRS , known as Jack , was a British-born geneticist and evolutionary biologist...
, applied statistical analysis to real-world examples of natural selection, such as the
evolution of industrial melanism in peppered mothsThe evolution of the peppered moth over the last two hundred years has been studied in detail. Originally, the vast majority of peppered moths had light colouration, which effectively camouflaged them against the light-coloured trees and lichens which they rested upon...
, and showed that natural selection worked at an even faster rate than Fisher assumed.
The American biologist
Sewall WrightSewall Green Wright was an American geneticist known for his influential work on evolutionary theory and also for his work on path analysis. With R. A. Fisher and J.B.S. Haldane, he was a founder of theoretical population genetics. He is the discoverer of the inbreeding coefficient and of...
, who had a background in
animal breedingAnimal breeding is a branch of animal science that addresses the evaluation of the genetic value of domestic livestock...
experiments, focused on combinations of interacting genes, and the effects of inbreeding on small, relatively isolated populations that exhibited
genetic driftGenetic drift or allelic drift is the change in the relative frequency with which a gene variant occurs in a population due to random sampling and chance: the alleles in offspring are a random sample of those in the parents, and chance has a role in determining whether a given individual survives...
. In 1932, Wright introduced the concept of an
adaptive landscapeIn evolutionary biology, fitness landscapes or adaptive landscapes are used to visualize the relationship between genotypes and reproductive success. It is assumed that every genotype has a well defined replication rate . This fitness is the "height" of the landscape...
and argued that genetic drift and inbreeding could drive a small, isolated sub-population away from an adaptive peak, allowing natural selection to drive it towards different adaptive peaks. The work of Fisher, Haldane and Wright founded the discipline of
population geneticsPopulation genetics is the study of the allele frequency distribution and change under the influence of the four evolutionary processes: natural selection, genetic drift, mutation and gene flow. It also takes account of population subdivision and population structure in space. As such, it attempts...
. This integrated natural selection with Mendelian genetics, which was the critical first step in developing a unified theory of how evolution worked.
Modern evolutionary synthesis
In the first few decades of the 20th century, most field naturalists continued to believe that Lamarckian and orthogenic mechanisms of evolution provided the best explanation for the complexity they observed in the living world. However, as the field of genetics continued to develop, those views became less tenable.
Theodosius DobzhanskyTheodosius Grygorovych Dobzhansky, also known as T. G. Dobzhansky, and sometimes Anglicized to Theodore Dobzhansky was a noted geneticist and evolutionary biologist, and a central figure in the field of evolutionary biology for his work in shaping the unifying modern evolutionary...
, a postdoctoral worker in T. H. Morgan's lab, had been influenced by the work on genetic diversity by
RussiaRussia , officially known as both Russia and the Russian Federation , is a country in northern Eurasia . It is a semi-presidential republic, comprising 83 federal subjects...
n geneticists such as
Sergei ChetverikovSergei Sergeevich Chetverikov was one of the early contributors to the development of the field of genetics. His research showed how early genetic theories applied to natural populations, and has therefore contributed towards the modern synthesis of evolutionary theory...
. He helped to bridge the divide between the foundations of
microevolutionMicroevolution is the occurrence of small-scale changes in allele frequencies in a population, over a few generations, also known as "change below the species level"....
developed by the population geneticists and the patterns of
macroevolutionMacroevolution is a scale of analysis of evolution in separated gene pools. Macroevolutionary studies focus on change that occurs at or above the level of species, in contrast with microevolution, which refers to smaller evolutionary changes within a species or population.The process of...
observed by field biologists, with his 1937 book
Genetics and the Origin of SpeciesGenetics and the Origin of Species is a 1937 book by the Ukrainian-American evolutionary biologist Theodosius Dobzhansky and one of the important books of the modern evolutionary synthesis...
. Dobzhansky examined the genetic diversity of wild populations and showed that, contrary to the assumptions of the population geneticists, these populations had large amounts of genetic diversity, with marked differences between sub-populations. The book also took the highly mathematical work of the population geneticists and put it into a more accessible form. In Great Britain
E.B. FordEdmund Brisco "Henry" Ford FRS Hon. FRCP was a British ecological geneticist. He was a leader among those British biologists who investigated the role of natural selection in nature. As a schoolboy Ford became interested in lepidoptera, the group of insects which includes butterflies and moths...
, the pioneer of
ecological geneticsEcological genetics is the study of genetics in the context of the interactions among organisms and between the organisms and their environment. While molecular genetics studies the structure and function of genes at a molecular level, ecological genetics studies phenotypic evolution in natural...
, continued throughout the 1930s and 1940s to demonstrate the power of selection due to ecological factors including the ability to maintain genetic diversity through
genetic polymorphismsPolymorphism in biology occurs when two or more clearly different phenotypes exist in the same population of a species — in other words, the occurrence of more than one form or morph...
such as human blood types. Ford's work would contribute to a shift in emphasis during the course of the modern synthesis towards
natural selectionNatural selection is the process by which heritable traits that make it more likely for an organism to survive and successfully reproduce become more common in a population over successive generations...
over
genetic driftGenetic drift or allelic drift is the change in the relative frequency with which a gene variant occurs in a population due to random sampling and chance: the alleles in offspring are a random sample of those in the parents, and chance has a role in determining whether a given individual survives...
.
Ernst Mayr was influenced by the work of the German biologist
Bernhard RenschBernhard Rensch was a German evolutionary biologist, and ornithologist who did field work in Indonesia and India. He is probably best known as one of the architects of the modern evolutionary synthesis, which he popularised in Germany...
on how local environmental factors influenced the geographic distribution of sub-species and closely related species. Mayr followed up on Dobzhansky's work with the 1942 book
Systematics and the Origin of Species, which emphasized the importance of
allopatric speciationAllopatric and allopatry are terms from biogeography, referring to organisms whose ranges are entirely separate, so that they do not occur in any one place together. If these organisms are closely related Allopatric and allopatry are terms from biogeography, referring to organisms whose ranges are...
in the formation of new species. This form of speciation occurs when the geographical isolation of a sub-population is followed by the development of mechanisms for
reproductive isolationAn important concept in evolutionary biology, reproductive isolation is a category of mechanisms that prevent two or more populations from exchanging genes. The separation of the gene pools of populations, under some conditions, can lead to the genesis of distinct species...
. Mayr also formulated the biological species concept that defined a species as a group of interbreeding or potentially interbreeding populations that were reproductively isolated from all other populations.
In the 1944 book
Tempo and Mode in EvolutionTempo and Mode in Evolution was George Gaylord Simpson's seminal contribution to the evolutionary synthesis, which integrated the facts of paleontology with those of genetics and natural selection....
,
George Gaylord SimpsonGeorge Gaylord Simpson was an American paleontologist. Simpson was perhaps the most influential paleontologist of the twentieth century, and a major participant in the modern evolutionary synthesis, contributing Tempo and mode in evolution , The meaning of evolution and The major features of...
showed that the fossil record was consistent with the irregular non-directional pattern predicted by the developing evolutionary synthesis, and that the linear trends that earlier paleontologists had claimed supported orthogenesis and neo-Lamarckism did not hold up to closer examination. In 1950,
G. Ledyard StebbinsGeorge Ledyard Stebbins, Jr. was an American botanist and geneticist who is widely regarded as one of the leading evolutionary biologists of the 20th century. Stebbins received his Ph.D. in botany from Harvard University in 1931. He went on to the University of California, Berkeley, where his work...
published
Variation and Evolution in PlantsVariation and Evolution in Plants, written by G. Ledyard Stebbins. was published in 1950; it is one of the key publications embodying the modern evolutionary synthesis, as the first comprehensive publication to discuss the relationship between genetics and natural selection in plants. The book has...
, which helped to integrate
botanyBotany, plant science, phytology, or plant biology is a branch of biology and is the scientific study of plant life and development...
into the synthesis. The emerging cross-disciplinary consensus on the workings of evolution would be known as the
modern evolutionary synthesisThe modern evolutionary synthesis is a union of ideas from several biological specialties which forms a logical account of evolution. This synthesis has been accepted by nearly all working biologists...
. It received its name from the book
Evolution: The Modern SynthesisEvolution: The Modern Synthesis, a 1942 book by Julian Huxley , is one of the most important books of the modern evolutionary synthesis.- Publication history :Allen & Unwin, London...
by
Julian HuxleySir Julian Sorell Huxley FRS was an English evolutionary biologist, humanist and internationalist. He was a proponent of natural selection, and a leading figure in the mid-twentieth century evolutionary synthesis...
.
The evolutionary synthesis provided a conceptual core — in particular, natural selection and Mendelian population genetics — that tied together many, but not all, biological disciplines. It helped establish the legitimacy of
evolutionary biologyEvolutionary biology is a sub-field of biology concerned with the origin of species from a common descent and descent of species, as well as their change, multiplication and diversity over time. Someone who studies evolutionary biology is known as an evolutionary biologist...
, a primarily historical science, in a scientific climate that favored experimental methods over historical ones. The synthesis also resulted in a considerable narrowing of the range of mainstream evolutionary thought (what Stephen Jay Gould called the "hardening of the synthesis"): by the 1950s, natural selection acting on genetic variation was virtually the only acceptable mechanism of evolutionary change (panselectionism), and macroevolution was simply considered the result of extensive microevolution.
1940s–1960s: Molecular biology and evolution
The middle decades of the 20th century saw the
rise of molecular biologyThe history of molecular biology begins in the 1930s with the convergence of various, previously distinct biological disciplines: biochemistry, genetics, microbiology, and virology...
, and with it an understanding of the chemical nature of genes as
sequences of DNAA DNA sequence or genetic sequence is a succession of letters representing the primary structure of a real or hypothetical DNA molecule or strand, with the capacity to carry information as described by the central dogma of molecular biology....
and their relationship, through the
genetic codeThe genetic code is the set of rules by which information encoded in genetic material is translated into proteins by living cells. A more precise term for the concept might be "genetic cipher". The code defines a mapping between tri-nucleotide sequences, called codons, and amino acids...
, to protein sequences. At the same time, increasingly powerful techniques for analyzing proteins, such as
protein electrophoresisIn medicine, protein electrophoresis is a method of analysing a mixture of proteins by means of gel electrophoresis, mainly in blood serum...
and
sequencingProteins are found in every cell and are essential to every biological process, protein structure is very complex: determining a protein's structure involves first protein sequencing - determining the amino acid sequences of its constituent peptides; and also determining what conformation it adopts...
, brought biochemical phenomena into realm of the synthetic theory of evolution. In the early 1960s, biochemists
Linus PaulingLinus Carl Pauling was an American chemist, peace activist, author, and educator. He was one of the most influential chemists in history and ranks among the most important scientists in any field of the 20th century. Pauling was among the first scientists to work in the fields of quantum...
and
Emile ZuckerkandlEmile Zuckerkandl is an Austrian-American biologist considered one of the founders of the field of molecular evolution. He is best known for introducing, with Linus Pauling, the concept of the molecular clock, which set the stage for the neutral theory of molecular evolution.-Life and...
proposed the molecular clock hypothesis: that sequence differences between homologous proteins could be used to calculate the time since two species diverged. By 1969,
Motoo Kimura, was a Japanese biologist best known for introducing the neutral theory of molecular evolution in 1968. He became one of the most influential theoretical population geneticists...
and others provided a theoretical basis for the molecular clock, arguing that — at the molecular level at least — most genetic mutations are neither harmful nor helpful and that
genetic driftGenetic drift or allelic drift is the change in the relative frequency with which a gene variant occurs in a population due to random sampling and chance: the alleles in offspring are a random sample of those in the parents, and chance has a role in determining whether a given individual survives...
, rather than
natural selectionNatural selection is the process by which heritable traits that make it more likely for an organism to survive and successfully reproduce become more common in a population over successive generations...
, is responsible for a large portion of genetic change: the
neutral theory of molecular evolutionThe neutral theory of molecular evolution is an influential theory, which was introduced with effect by Motoo Kimura in the late 1960s and early 1970s. The theory states that the vast majority of evolutionary changes at the molecular level are caused by random drift of selectively neutral mutants...
. Studies of protein differences
within species also brought molecular data to bear on population genetics by providing estimates of the level of heterozygosity in natural populations.
From the early 1960s, molecular biology was increasingly seen as a threat to the traditional core of evolutionary biology. Established evolutionary biologists — particularly Ernst Mayr, Theodosius Dobzhansky and G. G. Simpson, three of the architects of the modern synthesis — were extremely skeptical of molecular approaches, especially when it came to the connection (or lack thereof) to
natural selectionNatural selection is the process by which heritable traits that make it more likely for an organism to survive and successfully reproduce become more common in a population over successive generations...
. The molecular clock hypothesis and the neutral theory were particularly controversial, spawning the neutralist-selectionist debate over the relative importance of drift and selection, which continued into the 1980s without a clear resolution.
Gene-centered view
In the mid-1960s,
George C. WilliamsProfessor George Christopher Williams is an American evolutionary biologist.Williams is a professor emeritus of biology at the State University of New York at Stony Brook. He is best known for his vigorous critique of group selection. The work of Williams in this area, along with W. D...
strongly critiqued explanations of adaptations worded in terms of "survival of the species" (
group selectionIn evolutionary biology, group selection refers to the idea that alleles can become fixed or spread in a population because of the benefits they bestow on groups, regardless of the alleles' effect on the fitness of individuals within that group....
arguments). Such explanations were largely replaced by a
gene-centered view of evolutionThe gene-centered view of evolution, gene selection theory or selfish gene theory holds that natural selection acts through differential survival of competing genes, increasing the frequency of those alleles whose phenotypic effects successfully promote their own propagation...
, epitomized by the
kin selectionSome organisms tend to exhibit strategies that favor the reproductive success of their relatives, even at a cost to their own survival and/or reproduction. The classic example is a eusocial insect colony, with sterile females acting as workers to assist their mother in the production of additional...
arguments of
W. D. HamiltonWilliam Donald Hamilton FRS aka Bill Hamilton was a British evolutionary biologist whom Richard Dawkins praised as one of the greatest evolutionary theorists of the 20th century....
,
George R. PriceGeorge R. Price was an American population geneticist. Originally a physical chemist and later a science journalist, he moved to London in 1967, where he worked in theoretical biology at the Galton Laboratory, making three important contributions: first, rederiving W.D...
and
John Maynard SmithJohn Maynard Smith, F.R.S. was a British theoretical evolutionary biologist and geneticist. Originally an aeronautical engineer during the Second World War, he then took a second degree in genetics under the well-known biologist J.B.S. Haldane...
. This viewpoint would be summarized and popularized in the influential 1976 book
The Selfish GeneThe Selfish Gene is a book on evolution by Richard Dawkins, published in 1976. It builds upon the principal theory of George C. Williams's first book Adaptation and Natural Selection...
by
Richard DawkinsClinton Richard Dawkins, FRS, FRSL is a British ethologist, zoologist, Neo-Darwinian evolutionary biologist and theorist and a popular science author....
. Models of the period showed that group selection was severely limited in its strength; though newer models do admit the possibility of significant multi-level selection.
In 1973,
Leigh Van ValenLeigh M. Van Valen is an American evolutionary biologist. he is professor in the Department of Ecology and Evolution at the University of Chicago....
proposed the term "
Red QueenThe Red Queen's Hypothesis, Red Queen, "Red Queen's race" or "Red Queen Effect" is an evolutionary hypothesis. The term is taken from the Red Queen's race in Lewis Carroll's Through the Looking-Glass...
", which he took from
Through the Looking Glass by
Lewis Carroll Charles Lutwidge Dodgson , better known by the pen name Lewis Carroll , was an English author, mathematician, logician, Anglican deacon and photographer...
, to describe a scenario where a species involved in one or more
evolutionary arms raceIn evolutionary biology, an evolutionary arms race is an evolutionary struggle between competing sets of co-evolving genes that develop adaptations and counter-adaptations against each other, resembling an arms race, which are also examples of positive feedback...
s would have to constantly change just to keep pace with the species with which it was
co-evolvingIn a broad sense, biological coevolution is "the change of a biological object triggered by the change of a related object". Coevolution can occur at multiple levels of biology: it can be as microscopic as correlated mutations between amino acids in a protein, or as macroscopic as covarying traits...
. Hamilton, Williams and others suggested that this idea might explain the
evolution of sexual reproductionScientists currently have developed several competing hypotheses to explain the evolution of sexual reproduction. Many groups of organisms, notably the majority of animals and plants, reproduce sexually. The evolution of sex contains two related, yet distinct, themes: its origin and its maintenance...
: the increased genetic diversity caused by sexual reproduction would help maintain resistance against rapidly evolving parasites, thus making sexual reproduction common, despite the tremendous cost from the gene-centric point of view of a system where only half of an organism's
genomeIn modern molecular biology the genome refers to all of its hereditary information encoded in DNA .The genome includes both the genes and the non-coding sequences of the DNA. The term was adapted in 1920 by Hans Winkler, Professor of Botany at the University of Hamburg, Germany...
is passed on during reproduction. The gene-centric view has also led to an increased interest in Darwin's old idea of
sexual selectionSexual selection is the theory proposed by Charles Darwin that states that certain evolutionary traits can be explained by intraspecific competition. Darwin defined sexual selection as the effects of the "struggle between the individuals of one sex, generally the males, for the possession of the...
, and more recently in topics such as
sexual conflictSexual conflict occurs when the two sexes have conflicting optimal fitness strategies concerning reproduction, leading to evolutionary arms race between males and females...
and
intragenomic conflictThe selfish gene theory postulates that natural selection will increase the frequency of those genes whose phenotypic effects ensure their successful replication...
.
Sociobiology
W. D. Hamilton's work on kin selection contributed to the emergence of the discipline of
sociobiologySociobiology is a synthesis of scientific disciplines which attempts to explain social behavior in animal species by considering the Darwinian advantages specific behaviors may have. It is often considered a branch of biology and sociology, but also draws from ethology, anthropology, evolution,...
. The existence of
altruistic behaviorsAltruism is selfless concern for the welfare of others. It is a traditional virtue in many cultures, and a core aspect of various religious traditions such as Judaism, Christianity, Islam, Hinduism, Jainism, Buddhism, Confucianism, Sikhism, and many others. Also, altruism is a key aspect of many...
has been a difficult problem for evolutionary theorists from the beginning. Significant progress was made in 1964 when Hamilton formulated the inequality in
kin selectionSome organisms tend to exhibit strategies that favor the reproductive success of their relatives, even at a cost to their own survival and/or reproduction. The classic example is a eusocial insect colony, with sterile females acting as workers to assist their mother in the production of additional...
known as Hamilton's rule, which showed how
eusocialityEusociality is a term used for the highest level of social organization in a hierarchical classification....
in insects (the existence of sterile worker classes) and many other examples of altruistic behavior could have evolved through kin selection. Other theories followed, some derived from
game theoryGame theory is a branch of applied mathematics that is used in the social sciences, most notably in economics, as well as in biology, engineering, political science, international relations, computer science, and philosophy...
, such as
reciprocal altruismReciprocal altruism is a concept, introduced into evolutionary biology by Robert Trivers, which explains the evolution of cooperation as instances of mutually altruistic acts...
. In 1975, E.O. Wilson published the influential and highly controversial book
Sociobiology: The New SynthesisSociobiology: The New Synthesis is a book written by E. O. Wilson, which started the sociobiology debate, one of the great scientific controversies in biology of the 20th century...
which claimed evolutionary theory could help explain many aspects of animal, including human, behavior. Critics of sociobiology, including
Stephen Jay GouldStephen Jay Gould was an American paleontologist, evolutionary biologist, and historian of science. He was also one of the most influential and widely read writers of popular science of his generation. Gould spent most of his career teaching at Harvard University and working at the American Museum...
and
Richard LewontinRichard Charles "Dick" Lewontin is an American evolutionary biologist, geneticist and social commentator. A leader in developing the mathematical basis of population genetics and evolutionary theory, he pioneered the notion of using techniques from molecular biology such as gel electrophoresis to...
, claimed that sociobiology greatly overstated the degree to which complex human behaviors could be determined by genetic factors. They also claimed that the theories of sociobiologists often reflected their own ideological biases. Despite these criticisms, work has continued in sociobiology and the related discipline of
evolutionary psychologyEvolutionary psychology attempts to explain psychological traits—such as memory, perception, or language—as adaptations, that is, as the functional products of natural selection or sexual selection. Adaptationist thinking about physiological mechanisms, such as the heart, lungs, and immune system,...
, including work on other aspects of the altruism problem.
Evolutionary paths and processes
One of the most prominent debates arising during the 1970s was over the theory of
punctuated equilibriumPunctuated equilibrium is a theory in evolutionary biology which proposes that most sexually reproducing species will experience little evolutionary change for most of their geological history . When evolution occurs, it is localized in rare, rapid events of branching speciation...
.
Niles EldredgeNiles Eldredge is an American paleontologist, who, along with Stephen Jay Gould, proposed the theory of punctuated equilibrium in 1972.-Education:...
and
Stephen Jay GouldStephen Jay Gould was an American paleontologist, evolutionary biologist, and historian of science. He was also one of the most influential and widely read writers of popular science of his generation. Gould spent most of his career teaching at Harvard University and working at the American Museum...
proposed that there was a pattern of fossil species that remained largely unchanged for long periods (what they termed
stasis), interspersed with relatively brief periods of rapid change during
speciationSpeciation is the evolutionary process by which new biological species arise. The biologist Orator F. Cook seems to have been the first to coin the term 'speciation' for the splitting of lineages or 'cladogenesis,' as opposed to 'anagenesis' or 'phyletic evolution' occurring within lineages...
. Improvements in
sequencingIn genetics and biochemistry, sequencing means to determine the primary structure of an unbranched biopolymer. Sequencing results in a symbolic linear depiction known as a sequence which succinctly summarizes much of the atomic-level structure of the sequenced molecule.-DNA sequencing:DNA...
methods resulted in a large increase of sequenced
genomeIn modern molecular biology the genome refers to all of its hereditary information encoded in DNA .The genome includes both the genes and the non-coding sequences of the DNA. The term was adapted in 1920 by Hans Winkler, Professor of Botany at the University of Hamburg, Germany...
s, allowing the testing and refining of evolutionary theories using this huge amount of genome data. Comparisons between these genomes provide insights into the molecular mechanisms of speciation and adaptation. These genomic analyses have produced fundamental changes in the understanding of the
evolutionary history of lifeThe evolutionary history of life on Earth traces the processes by which living and fossil organisms evolved. It stretches back over , possibly as far as , and evolution continues, even in humans. All present-day organisms use the same large set of complex chemical reactions, which indicates that...
, such as the proposal of the
three-domain systemThe three-domain system is a biological classification introduced by Carl Woese in 1990 that divides cellular life forms into archaea, bacteria, and eukaryote domains. In particular, it emphasizes the separation of prokaryotes into two groups, originally called Eubacteria and Archaebacteria...
by
Carl WoeseCarl Richard Woese is an American microbiologist and physicist. Woese is famous for defining the Archaea in 1977 by phylogenetic taxonomy of 16S ribosomal RNA, a technique pioneered by Woese and which is now standard practice...
. Advances in computational hardware and software allow the testing and extrapolation of increasingly advanced evolutionary models and the development of the field of
systems biologySystems biology is a biology-based inter-disciplinary study field that focuses on the systematic study of complex interactions in biological systems, thus using a new perspective to study them. Particularly from year 2000 onwards, the term is used widely in the biosciences, and in a variety of...
. One of the results has been an exchange of ideas between theories of biological evolution and the field of
computer scienceComputer science is the study of the theoretical foundations of information and computation, and of practical techniques for their implementation and application in computer systems. It is frequently described as the systematic study of algorithmic processes that create, describe and transform...
known as
evolutionary computationIn computer science, evolutionary computation is a subfield of artificial intelligence that involves combinatorial optimization problems....
, which attempts to mimic biological evolution for the purpose of developing new computer algorithms. Discoveries in
biotechnologyBiotechnology is technology based on biology, agriculture, food science, and medicine. Modern use of the term usually refers to genetic engineering as well as cell- and tissue culture technologies...
now allow the modification of entire genomes, advancing evolutionary studies to the level where future experiments may involve the creation of entirely synthetic organisms.
Microbiology and horizontal gene transfer
MicrobiologyMicrobiology is the study of microorganisms, which are unicellular or cell-cluster microscopic organisms. This includes eukaryotes such as fungi and protists, and prokaryotes. Viruses, though not strictly classed as living organisms, are also studied...
was largely ignored by early evolutionary theory. This was due to the paucity of morphological traits and the lack of a species concept in microbiology, particularly amongst
prokaryoteThe prokaryotes are a group of organisms that lack a cell nucleus , or any other membrane-bound organelles. They differ from the eukaryotes, which have a cell nucleus. Most are unicellular, but a few prokaryotes such as myxobacteria have multicellular stages in their life cycles...
s. Now, evolutionary researchers are taking advantage of their improved understanding of microbial physiology and ecology, produced by the comparative ease of microbial
genomicsGenomics is the study of the genomes of organisms. The field includes intensive efforts to determine the entire DNA sequence of organisms and fine-scale genetic mapping efforts. The field also includes studies of intragenomic phenomena such as heterosis, epistasis, pleiotropy and other...
, to explore the taxonomy and evolution of these organisms. These studies are revealing unanticipated levels of diversity amongst microbes.
One particularly important outcome from studies on microbial evolution was the discovery in Japan of
horizontal gene transferHorizontal gene transfer , also Lateral gene transfer , is any process in which an organism incorporates genetic material from another organism without being the offspring of that organism. By contrast, vertical transfer occurs when an organism receives genetic material from its ancestor, e.g...
in 1959. This transfer of genetic material between different species of bacteria was first recognized since it played a major role in the spread of
antibiotic resistanceAntibiotic resistance is the ability of a microorganism to withstand the effects of antibiotics. It is a specific type of drug resistance. Antibiotic resistance evolves via natural selection acting upon random mutation, but it can also be engineered by applying an evolutionary stress on a population...
. More recently, as knowledge of
genomeIn modern molecular biology the genome refers to all of its hereditary information encoded in DNA .The genome includes both the genes and the non-coding sequences of the DNA. The term was adapted in 1920 by Hans Winkler, Professor of Botany at the University of Hamburg, Germany...
s has continued to expand, it has been suggested that lateral transfer of genetic material has played an important role in the evolution of all organisms. These high levels of horizontal gene transfer have led to suggestions that the family tree of today's organisms, the so-called "tree of life", is more similar to an interconnected web or net. Indeed, as part of the
endosymbiotic theoryThe endosymbiotic theory concerns the origins of mitochondria and plastids , which are organelles of eukaryotic cells. According to this theory, these organelles originated as separate prokaryotic organisms that were taken inside the cell as endosymbionts...
for the origin of
organelleIn cell biology, an organelle is a specialized subunit within a cell that has a specific function, and is usually separately enclosed within its own lipid membrane....
s, horizontal gene transfer has been a critical step in the evolution of
eukaryoteA eukaryote is an organism whose cells contain complex structures enclosed within membranes. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear envelope, within which the genetic material is carried...
s such as fungi, plants, and animals.
Evolutionary developmental biology
In the 1980s and 1990s the tenets of the
modern evolutionary synthesisThe modern evolutionary synthesis is a union of ideas from several biological specialties which forms a logical account of evolution. This synthesis has been accepted by nearly all working biologists...
came under increasing scrutiny. There was a renewal of
structuralistStructuralism is an approach to the human sciences that attempts to analyze a specific field as a complex system of interrelated parts. It began in linguistics with the work of Ferdinand de Saussure...
themes in evolutionary biology in the work of biologists such as
Brian GoodwinBrian Carey Goodwin was a Canadian mathematician and a biologist, a Professor Emeritus at the Open University and a key founder of a branch of mathematical biology known as theoretical biology that focuses on the methods of mathematics and physics to understand processes in biology-Biography:Brian...
and
Stuart KauffmanStuart Alan Kauffman is an American theoretical biologist and complex systems researcher concerning the origin of life on Earth...
, which incorporated ideas from
cyberneticsCybernetics is the interdisciplinary study of the structure of regulatory systems. Cybernetics is closely related to control theory and systems theory...
and
systems theorySystems theory is an interdisciplinary theory about the nature of complex systems in nature, society, and science, and is a framework by which one can investigate and/or describe any group of objects that work together to produce some result. This could be a single organism, any organization or...
, and emphasized the
self-organizingSelf-organization is a process of attraction and repulsion in which the internal organization of a system, normally an open system, increases in complexity without being guided or managed by an outside source...
processes of development as factors directing the course of evolution. The evolutionary biologist
Stephen Jay GouldStephen Jay Gould was an American paleontologist, evolutionary biologist, and historian of science. He was also one of the most influential and widely read writers of popular science of his generation. Gould spent most of his career teaching at Harvard University and working at the American Museum...
revived earlier ideas of
heterochronyIn biology, heterochrony is defined as a developmental change in the timing of events, leading to changes in size and shape. There are two main components, namely the onset and offset of a particular process, and the rate at which the process operates...
, alterations in the relative rates of developmental processes over the course of evolution, to account for the generation of novel forms, and, with the evolutionary biologist
Richard LewontinRichard Charles "Dick" Lewontin is an American evolutionary biologist, geneticist and social commentator. A leader in developing the mathematical basis of population genetics and evolutionary theory, he pioneered the notion of using techniques from molecular biology such as gel electrophoresis to...
, wrote an influential paper in 1979 suggesting that a change in one biological structure, or even a structural novelty, could arise incidentally as an accidental result of selection on another structure, rather than through direct selection for that particular adaptation. They called such incidental structural changes "
spandrelsSpandrel is a term used in evolutionary biology to describe a phenotypic characteristic that is a byproduct of the evolution of some other character, rather than a direct product of adaptive selection...
" after an architectural feature. Later, Gould and Vrba discussed the acquisition of new functions by novel structures arising in this fashion, calling them "
exaptationExaptation, cooption, and preadaptation are related terms referring to shifts in the function of a trait during evolution. For example, a trait can evolve because it served one particular function, but subsequently it may come to serve another. Exaptations are common in both anatomy and behavior...
s".
Molecular data regarding the mechanisms underlying
developmentDevelopmental biology is the study of the process by which organisms grow and develop. Modern developmental biology studies the genetic control of cell growth, differentiation and "morphogenesis," which is the process that gives rise to tissues, organs and anatomy.Developmental biology is that...
accumulated rapidly during the 1980s and '90s. It became clear that the diversity of animal morphology was not the result of different sets of proteins regulating the development of different animals, but from changes in the deployment of a small set of proteins that were common to all animals. These proteins became known as the "developmental toolkit". Such perspectives influenced the disciplines of
phylogeneticsIn biology, phylogenetics is the study of evolutionary relatedness among various groups of organisms , which is discovered through molecular sequencing data and morphological data matrices...
,
paleontologyPaleontology
[from Greek: παλαιός "old, ancient", ὄν, ὀντ- "being, creature", and λόγος "speech, thought"] is the study of prehistoric life, including organisms' evolution and interactions with each other and their environments...
and comparative developmental biology, and spawned the new discipline of
evolutionary developmental biologyEvolutionary developmental biology is a field of biology that compares the developmental processes of different animals and plants in an attempt to determine the ancestral relationship between organisms and how developmental processes evolved...
.
More recent work in this field by
Mary Jane West-EberhardMary Jane West-Eberhard is an American theoretical biologist noted for arguing that phenotypic and developmental plasticity played a key role in shaping animal evolution and speciation...
has emphasized
phenotypic and developmental plasticityPhenotypic plasticity is the ability of an organism to change its phenotype in response to changes in the environment. Such plasticity in some cases expresses as several highly morphologically distinct results; in other cases, a continuous norm of reaction describes the functional interrelationship...
. It has been suggested, for example, that the rapid emergence of basic animal body plans in the
Cambrian explosionThe Cambrian explosion or Cambrian radiation was the seemingly rapid appearance of most major groups of complex animals around , as evidenced by the fossil record. This was accompanied by a major diversification of other organisms, including animals, phytoplankton, and calcimicrobes...
was due in part to changes in the environment acting on inherent material properties of cell aggregates, such as differential
cell adhesionCellular adhesion is the binding of a cell to a surface, extracellular matrix or another cell using cell adhesion molecules such as selectins, integrins, and cadherins.- Process :...
and
biochemical oscillationA chemical clock is a complex mixture of reacting chemical compounds in which the concentration of one or more components exhibits periodic changes. In cases where one of the reagents has a visible color, crossing a concentration threshold can lead to an abrupt color change, which may be used to...
. The resulting forms were later stabilized by natural selection. Experimental and theoretical research on these and related ideas have been presented in the multi-authored volume
Origination of Organismal FormOrigination of Organismal Form: Beyond the Gene in Developmental and Evolutionary Biology is a book published in 2003 edited by Gerd B. Müller and Stuart A. Newman. It explores the multiple factors that may have been responsible for the origination of biological form in multicellular life...
.
Omega point
Pierre Teilhard de ChardinPierre Teilhard de Chardin was a French philosopher and Jesuit priest who trained as a paleontologist and geologist and took part in the discovery of Peking Man...
's non-scientific
Omega point theoryOmega Point is a term invented by the French Jesuit Pierre Teilhard de Chardin to describe a supreme level of complexity and consciousness towards which the universe appears to be evolving. The maximum level is only given to man made gods such as God, Allah, Yahweh, or Brahman...
describes the gradual development of the
universeThe Universe comprises everything that physically exists, the entirety of space and time, all forms of matter and energy, and the physical laws and constants that govern them...
from subatomic particles to human society, which he viewed as its final stage and goal.
Gaia hypothesis
Teilhard de Chardin's ideas have been seen as being connected to the more specific
Gaia theoryThe Gaia hypothesis is an ecological hypothesis proposing that the biosphere and the physical components of the Earth are closely integrated to form a complex interacting system that maintains the climatic and biogeochemical conditions on Earth in a preferred homeostasis...
by
James LovelockJames Ephraim Lovelock, CH, CBE, FRS is an independent scientist, author, researcher, environmentalist, and futurist who lives in Devon, England...
, who proposed that the living and nonliving parts of Earth can be viewed as a complex interacting system with similarities to a single organism. The Gaia hypothesis has also been viewed by
Lynn MargulisLynn Margulis is an American biologist and University Professor in the Department of Geosciences at the University of Massachusetts Amherst...
and others as an extension of
endosymbiosisAn endosymbiont is any organism that lives within the body or cells of another organism, i.e. forming an endosymbiosis...
and
exosymbiosisEctosymbiosis is symbiosis in which the symbiont lives on the body surface of the host, including internal surfaces such as the lining of the digestive tube and the ducts of glands....
. This modified hypothesis postulates that all living things have a regulatory effect on the Earth's environment that promotes life overall.
Transhumanism
FuturistsFuturists, or futurologists, are those who speculate about the future.- Definition :The Oxford English Dictionary traces earliest English usage of the term 'futurist' to 1842, referring to Christian scriptural futurists...
have often viewed scientific and technological progress as a continuation of biological evolution. Among these,
transhumanistsTranshumanism is an international intellectual and cultural movement supporting the use of science and technology to improve human mental and physical characteristics and capacities. The movement regards aspects of the human condition, such as disability, suffering, disease, aging, and involuntary...
often view such technological evolution itself as a goal in their philosophy, possibly in the form of a
technological singularityTechnological singularity is a term used with varying meanings related to self-improving artificial intelligence, superintelligence, breakdowns in the predictability of the future, accelerating change of the exponential or superexponential/catastrophic sort, and more generic "big events" in...
.
See also
- Faith and rationality
Faith and rationality are two modes of belief that exist in varying degrees of conflict or compatibility. Faith is belief in inspiration, revelation, or authority. Rationality is belief based on reason or evidence....
- Galápagos Islands
The Galápagos Islands are an archipelago of volcanic islands distributed around the equator in the Pacific Ocean, 972 km west of continental Ecuador...
- The Voyage of the Beagle
The Voyage of the Beagle is a title commonly given to the book written by Charles Darwin published in 1839 as his Journal and Remarks, which brought him considerable fame and respect...
External links