Macroevolution is a scale of analysis 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 separated
gene poolIn population genetics, a gene pool is the complete set of unique alleles in a species or population.- Description :A large gene pool indicates extensive genetic diversity, which is associated with robust populations that can survive bouts of intense selection...
s. Macroevolutionary studies focus on change that occurs at or above the level of
speciesIn biology, a species is:* a taxonomic rank or* a unit at that rank ....
, in contrast with
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"....
, which refers to smaller evolutionary changes (typically described as changes in allele frequencies)
within a species or population.
The process of
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...
may fall within the purview of either, depending on the forces thought to drive it.
Macroevolution is a scale of analysis 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 separated
gene poolIn population genetics, a gene pool is the complete set of unique alleles in a species or population.- Description :A large gene pool indicates extensive genetic diversity, which is associated with robust populations that can survive bouts of intense selection...
s. Macroevolutionary studies focus on change that occurs at or above the level of
speciesIn biology, a species is:* a taxonomic rank or* a unit at that rank ....
, in contrast with
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"....
, which refers to smaller evolutionary changes (typically described as changes in allele frequencies)
within a species or population.
The process of
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...
may fall within the purview of either, depending on the forces thought to drive it.
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...
,
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...
,
comparative genomicsComparative genomics is the study of the relationship of genome structure and function across different biological species or strains. Comparative genomics is an attempt to take advantage of the information provided by the signatures of selection to understand the function and evolutionary...
and
genomic phylostratigraphyGenomic phylostratigraphy is a statistical approach for reconstruction of macroevolutionary trends based on the principle of founder gene formation and punctuated emergence of protein families. Phylostratigraphy, a novel statistical method, was developed by Tomislav Domazet-Lošo at the Ruđer...
contribute most of the evidence for the patterns and processes that can be classified as macroevolution. An example of macroevolution is the appearance of feathers during the evolution of birds from theropod dinosaurs.
The evolutionary course of
EquidaeEquidae is the taxonomic family of horses and related animals, including the extant horses, donkeys, and zebras, and many other species known only from fossils. All extant species are in the genus Equus...
(wide family including all horses and related animals) is often viewed as a typical example of macroevolution. The earliest known genus,
HyracotheriumHyracotherium was a genus of very small perissodactyl ungulates that lived in the Northern Hemisphere, with species ranging throughout Asia, Europe, and North America during the Early to Mid Eocene, about 60 to 45 million years ago...
(now reclassified as a palaeothere), was a herbivore animal resembling a dog that lived in the early
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...
. As its habitat transformed into an open arid grassland, selective pressure required that the animal become a fast grazer. Thus elongation of legs and head as well as reduction of toes gradually occurred, producing the only
extantExtant is a term commonly used in biology to refer to taxa that are still in existence . The term extant contrasts with extinct. For example, Brandt's Cormorant is an extant species, while the Spectacled Cormorant is an extinct species...
genus of Equidae,
EquusEquus is a genus of animals in the family Equidae that includes horses, donkeys, and zebras. Within Equidae, Equus is the only extant genus. Like Equidae more broadly, Equus has numerous extinct species known only from fossils...
.
Abrupt transformations from a biologic system to another, for example the passing of life from water into land or the transition from
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 to
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...
s, are rare and follow radial adaptation which sometimes leads to
convergent evolutionConvergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, birds and bats do, and are capable of powered flight. The wings are similar in...
. The first organisms to occupy totally new habitats meet little competition and are able to exploit a plethora of available
nicheNiche may refer to:*Niche , an exedra or an apse that has been reduced in size;*Ecological niche, a term describing the relational position of an organism's species*Niche market, a focused, targetable portion of a market sector....
s. Few major biological types have emerged during 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...
and most of them survive till today.
Origin of the term
Russian
entomologistEntomology is the scientific study of insects, a branch of arthropodology...
Yuri Filipchenkothumb|Yuri FilipchenkoYuri Filipchenko was a Russian entomologist and coiner of the terms microevolution and macroevolution. Mentor of Theodosius Dobzhansky...
(or Philipchenko, depending on the transliteration) first coined the terms "macroevolution" and "microevolution" in 1927 in his German language work, "Variabilität und Variation". Since the inception of the two terms, their meanings have been revised several times and the term macroevolution fell into limited disfavour when it was taken over by such writers as the geneticist
Richard GoldschmidtRichard Benedict Goldschmidt was a German-born American geneticist. He is considered the first to integrate genetics, development, and evolution . He pioneered understanding of reaction norms, genetic assimilation, dynamical genetics, sex determination, and heterochrony...
(1940) and the paleontologist
Otto SchindewolfOtto Heinrich Schindewolf was a German paleontologist who studied the evolution of corals and cephalopods....
to describe their
orthogeneticOrthogenesis, 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...
theories.
As a result, apart from Dobzhansky,
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...
and
Ernst MayrErnst Walter Mayr , was one of the 20th century's leading evolutionary biologists. He was also a renowned taxonomist, tropical explorer, ornithologist, historian of science, and naturalist...
, very few neo-Darwinian writers used the term, preferring instead to talk of evolution as changes in allele frequencies without mention of the level of the changes (above species level or below). Those who did were generally working within the continental European traditions (as Dobzhansky,
Ernst MayrErnst Walter Mayr , was one of the 20th century's leading evolutionary biologists. He was also a renowned taxonomist, tropical explorer, ornithologist, historian of science, and naturalist...
,
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...
,
Richard GoldschmidtRichard Benedict Goldschmidt was a German-born American geneticist. He is considered the first to integrate genetics, development, and evolution . He pioneered understanding of reaction norms, genetic assimilation, dynamical genetics, sex determination, and heterochrony...
, and
Otto SchindewolfOtto Heinrich Schindewolf was a German paleontologist who studied the evolution of corals and cephalopods....
were) and those who didn't were generally working within the Anglo-American tradition (such as
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...
and
Richard DawkinsClinton Richard Dawkins, FRS, FRSL is a British ethologist, zoologist, Neo-Darwinian evolutionary biologist and theorist and a popular science author....
). Hence, use of the term "macroevolution" is sometimes wrongly used as a litmus test of whether the writer is "properly" neo-Darwinian or not.
Macroevolution and the modern evolutionary synthesis
Within the
Modern 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...
school of thought, macroevolution is thought of as the compounded effects of microevolution. Thus, the distinction between micro- and macroevolution is not a fundamental one the only difference between them is of time and scale; Ernst W. Mayr stated that "transspecific evolution is nothing but an extrapolation
and magnification of the events that take place within populations and species...it is misleading to make a distinction between the causes of micro- and macroevolution”. However, it should be noted that time is not a necessary distinguishing factor macroevolution can happen without gradual compounding of small changes;
whole-genome duplicationPolyploidy occurs in cells and organisms when there are more than two paired sets of chromosomes.Most organisms are normally diploid, meaning they have two sets of chromosomes — one set inherited from each parent. Polyploidy may occur due to abnormal cell division. It is most commonly found in...
can result in speciation occurring over a single generation - this is especially common in plants.
Changes in the genes regulating development have also been proposed as being important in producing speciation through large and relatively sudden changes in animals' morphology.
Research topics
Some examples of subjects whose study falls within the realm of macroevolution:
- Adaptive radiation
An adaptive radiation is a rapid evolutionary radiation characterized by an increase in the morphological and ecological diversity of a single, rapidly diversifying lineage. Phenotypes adapt in response to the environment, with new and useful traits arising...
s such as 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...
.
- Changes in biodiversity through time.
- Genomic evolution
The Evolution of the Genome is a book edited by Dr. T. Ryan Gregory of the University of Guelph, in Guelph, Ontario, Canada, covering a wide range of topics in the study of genome evolution...
, like 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...
, genome fusions in endosymbioses, and adaptive changes in genome size.
- Mass extinctions.
- Speciation
Speciation 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...
and 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...
rates.
- The debate between punctuated equilibrium
Punctuated 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...
and gradualismGradualism is the belief that changes occur, or ought to occur, slowly in the form of gradual steps -Politics and society:...
.
- The role of development in shaping evolution, particularly such topics as heterochrony
In 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...
and phenotypic 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...
.
Criticisms of macroevolution
The term "macroevolution" frequently arises within the context of the
evolution/creation debateThe creation–evolution controversy is a recurring theological and cultural-political dispute about the origins of the Earth, humanity, life, and the universe, between those who espouse the validity and/or superiority of literal interpretations of a creation myth, and the proponents of evolution,...
, usually used by creationists alleging a significant difference between the evolutionary changes observed in field and laboratory studies and the larger scale macroevolutionary changes that scientists believe to have taken thousands or millions of years to occur. They may accept that evolutionary change is possible within species ("microevolution"), but deny that one species can evolve into another ("macroevolution").
These arguments are rejected by
mainstream scienceThe scientific community consists of the total body of scientists, its relationships and interactions. It is normally divided into "sub-communities" each working on a particular field within science. Objectivity is expected to be achieved by the scientific method...
, which holds that there is ample evidence that macroevolution has occurred in the past. The consensus of the scientific community is that the alleged micro-macro division is an artificial construct made by creationists and does not accurately reflect the actual processes of evolution. Evolutionary theory (including macroevolutionary change) remains the dominant scientific paradigm for explaining the origins of
EarthEarth is the third planet from the Sun. It is the fifth largest of the eight planets in the solar system, and the largest of the terrestrial planets in the Solar System in terms of diameter, mass and density...
's biodiversity. Its occurrence, while controversial with the public at large, is not disputed within the scientific community.
While details of macroevolution are continuously studied by the
scientific communityThe scientific community consists of the total body of scientists, its relationships and interactions. It is normally divided into "sub-communities" each working on a particular field within science. Objectivity is expected to be achieved by the scientific method...
, the overall theory behind macroevolution (i.e.
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....
) has been overwhelmingly consistent with empirical data. Predictions of empirical data from the theory of common descent have been so consistent that biologists often refer to it as the "
fact of evolutionThe statement "evolution is both a theory and a fact" is often seen in biological literature.The "fact of evolution" refers to the changes in the genetic material of a population of biological organisms over time, which are known to have occurred through scientific observations and experiments...
".
Nicholas Matzke and
Paul R. GrossPaul R. Gross is a biologist and author, perhaps best known to the general public for Higher Superstition , written with Norman Levitt. Gross is the University Professor of Life Sciences at the University of Virginia; he previously served the university as Provost and Vice-President...
have accused
creationistsCreationism refers to the religious belief that humanity, life, the Earth, and the universe were created in some form by a supernatural being or beings, commonly a single deity...
of using "strategically elastic" definitions of micro- and macroevolution when discussing the topic. The actual definition of macroevolution accepted by scientists is "any change at the species level or above" (phyla, group, etc.) and microevolution is "any change below the level of species." Matzke and Gross state that many creationist critics define macroevolution as something that cannot be attained, as these critics describe any observed evolutionary change as "just microevolution".
External links