Sewall Green Wright was an American
geneticistA geneticist is a biologist who studies genetics, the science of genes, heredity, and variation of organisms. A geneticist can be employed as a researcher or lecturer. Some geneticists perform experiments and analyze data to interpret the inheritance of skills. A geneticist is also a Consultant or...
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 methods of computing it in pedigrees. He extended this work to populations, computing the amount of inbreeding of members of populations as a result of random
genetic driftGenetic drift or allelic drift is the change in the frequency of a gene variant in a population due to random sampling.The alleles in the offspring are a sample of those in the parents, and chance has a role in determining whether a given individual survives and reproduces...
, and he and Fisher pioneered methods for computing the distribution of gene frequencies among populations as a result of the interaction of
natural selectionNatural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....
,
mutationIn molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome or the DNA or RNA sequence of a virus. They can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic...
, migration and genetic drift. The work of Fisher, Wright, and Haldane on theoretical population genetics was a major step in the development of the
modern evolutionary synthesisThe modern evolutionary synthesis is a union of ideas from several biological specialties which provides a widely accepted account of evolution...
of genetics with evolution. Wright also made major contributions to mammalian genetics and biochemical genetics.
Biography
Sewall Wright was born in
Melrose-Government:Robert J. Dolan is the mayor. Melrose is represented in the Massachusetts House of Representatives by Paul Brodeur . Katherine Clark is the state senator for wards 1 through 5 and Thomas McGee is the state senator for wards 6 and 7. Melrose is part of the seventh Congressional...
,
MassachusettsThe Commonwealth of Massachusetts is a state in the New England region of the northeastern United States of America. It is bordered by Rhode Island and Connecticut to the south, New York to the west, and Vermont and New Hampshire to the north; at its east lies the Atlantic Ocean. As of the 2010...
to Philip Green Wright and Elizabeth Quincy Sewall Wright. His parents were first cousins, an interesting fact in light of Wright's later research on
inbreedingInbreeding is the reproduction from the mating of two genetically related parents. Inbreeding results in increased homozygosity, which can increase the chances of offspring being affected by recessive or deleterious traits. This generally leads to a decreased fitness of a population, which is...
. The family moved three years later after Philip accepted a teaching job at
Lombard College-History:Lombard College was founded in 1853 by the Universalist Church as the Illinois Liberal Institute. In 1855, however, a major fire damaged much of the college, placing its future at risk, but a large gift from Benjamin Lombard, an Illinois farmer and businessman, rescued the institution,...
, a Universalist college in Galesburg, Illinois.
As a child, Wright helped his father and brother print and publish an early book of poems by his father's student
Carl SandburgCarl Sandburg was an American writer and editor, best known for his poetry. He won three Pulitzer Prizes, two for his poetry and another for a biography of Abraham Lincoln. H. L. Mencken called Carl Sandburg "indubitably an American in every pulse-beat."-Biography:Sandburg was born in Galesburg,...
.
He was the oldest of three gifted brothers—the others being the aeronautical engineer
Theodore Paul WrightTheodore Paul Wright was a U.S. aeronautical engineer and educator. Born in Galesburg, Illinois, he served as acting president of Cornell University in 1951. Theodore P...
and the political scientist
Quincy WrightPhilip Quincy Wright was an American political scientist known for his pioneering work and expertise in international law and international relations.- Biography :...
. From an early age Wright had a love and talent for
mathematicsMathematics is the study of quantity, space, structure, and change. Mathematicians seek out patterns and formulate new conjectures. Mathematicians resolve the truth or falsity of conjectures by mathematical proofs, which are arguments sufficient to convince other mathematicians of their validity...
and
biologyBiology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. Biology is a vast subject containing many subdivisions, topics, and disciplines...
. Wright attended
Galesburg High SchoolGalesburg High School is a public high school in Galesburg, Illinois. Galesburg High School was established in 1861 in downtown Galesburg. It has since moved to Fremont Street on the west side of town...
and graduated in 1906. He then enrolled in
Lombard College-History:Lombard College was founded in 1853 by the Universalist Church as the Illinois Liberal Institute. In 1855, however, a major fire damaged much of the college, placing its future at risk, but a large gift from Benjamin Lombard, an Illinois farmer and businessman, rescued the institution,...
where his father taught, to study
mathematicsMathematics is the study of quantity, space, structure, and change. Mathematicians seek out patterns and formulate new conjectures. Mathematicians resolve the truth or falsity of conjectures by mathematical proofs, which are arguments sufficient to convince other mathematicians of their validity...
. He was influenced greatly by Professor Wilhelmine Entemann Key, one of the first women to receive a
Ph.D.A doctorate is an academic degree or professional degree that in most countries refers to a class of degrees which qualify the holder to teach in a specific field, A doctorate is an academic degree or professional degree that in most countries refers to a class of degrees which qualify the holder...
in
biologyBiology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. Biology is a vast subject containing many subdivisions, topics, and disciplines...
. Wright received his Ph.D. from
Harvard UniversityHarvard University is a private Ivy League university located in Cambridge, Massachusetts, United States, established in 1636 by the Massachusetts legislature. Harvard is the oldest institution of higher learning in the United States and the first corporation chartered in the country...
, where he worked at the
Bussey InstituteThe Bussey Institute was a respected biological institute at Harvard University. It was named for Benjamin Bussey, who, in 1835, endowed the establishment of an undergraduate school of agriculture and horticulture and donated land in Jamaica Plain, Massachusetts that became the Arnold Arboretum...
with the pioneering mammalian geneticist William Ernest Castle investigating the inheritance of coat colors in mammals. He worked for the U.S. Department of Agriculture until 1925, when he joined the Department of Zoology at the
University of ChicagoThe University of Chicago is a private research university in Chicago, Illinois, USA. It was founded by the American Baptist Education Society with a donation from oil magnate and philanthropist John D. Rockefeller and incorporated in 1890...
. He remained there until his retirement in 1955, when he moved to the
University of Wisconsin–MadisonThe University of Wisconsin–Madison is a public research university located in Madison, Wisconsin, United States. Founded in 1848, UW–Madison is the flagship campus of the University of Wisconsin System. It became a land-grant institution in 1866...
. He received many honors in his long career, including the
National Medal of ScienceThe National Medal of Science is an honor bestowed by the President of the United States to individuals in science and engineering who have made important contributions to the advancement of knowledge in the fields of behavioral and social sciences, biology, chemistry, engineering, mathematics and...
(1966), the
Balzan PrizeThe International Balzan Prize Foundation awards four annual monetary prizes to people or organisations who have made outstanding achievements in the fields of humanities, natural sciences, culture, as well as for endeavours for peace and the brotherhood of man.-Rewards and assets:Each year the...
(1984), and the
Darwin MedalThe Darwin Medal is awarded by the Royal Society every alternate year for "work of acknowledged distinction in the broad area of biology in which Charles Darwin worked, notably in evolution, population biology, organismal biology and biological diversity". First awarded in 1890, it was created in...
of the
Royal SocietyThe Royal Society of London for Improving Natural Knowledge, known simply as the Royal Society, is a learned society for science, and is possibly the oldest such society in existence. Founded in November 1660, it was granted a Royal Charter by King Charles II as the "Royal Society of London"...
(1980). He was a member of the
National Academy of SciencesThe National Academy of Sciences is a corporation in the United States whose members serve pro bono as "advisers to the nation on science, engineering, and medicine." As a national academy, new members of the organization are elected annually by current members, based on their distinguished and...
and a Foreign Member of the Royal Society. For his work on genetics of evolutionary processes-, Wright was awarded the
Daniel Giraud Elliot MedalThe Daniel Giraud Elliot Medal is awarded by the U.S. National Academy of Sciences "for meritorious work in zoology or paleontology published in a three- to five-year period." Named after Daniel Giraud Elliot, it was first awarded in 1917....
from the National Academy of Sciences in 1945.
Wright married Louise Lane Williams (1895–1975) in 1921. They had three children: Richard, Robert, and Elizabeth.
Scientific achievements and credits
His papers on
inbreedingInbreeding is the reproduction from the mating of two genetically related parents. Inbreeding results in increased homozygosity, which can increase the chances of offspring being affected by recessive or deleterious traits. This generally leads to a decreased fitness of a population, which is...
,
mating systemA mating system is a way in which a group is structured in relation to sexual behaviour. The precise meaning depends upon the context. With respect to higher animals, it specifies which males mate with which females, under which circumstances; recognised animal mating systems include monogamy,...
s, and
genetic driftGenetic drift or allelic drift is the change in the frequency of a gene variant in a population due to random sampling.The alleles in the offspring are a sample of those in the parents, and chance has a role in determining whether a given individual survives and reproduces...
make him a principal founder of
theoretical population geneticsPopulation genetics is the study of allele frequency distribution and change under the influence of the four main evolutionary processes: natural selection, genetic drift, mutation and gene flow. It also takes into account the factors of recombination, population subdivision and population...
, along with R. A. Fisher and
J. B. S. HaldaneJohn Burdon Sanderson Haldane FRS , known as Jack , was a British-born geneticist and evolutionary biologist. A staunch Marxist, he was critical of Britain's role in the Suez Crisis, and chose to leave Oxford and moved to India and became an Indian citizen...
. Their theoretical work is the origin of the
modern evolutionary synthesisThe modern evolutionary synthesis is a union of ideas from several biological specialties which provides a widely accepted account of evolution...
or neodarwinian synthesis. Wright was the inventor/discoverer of the inbreeding coefficient and
F-statisticsIn population genetics, F-statistics describe the level of heterozygosity in a population; more specifically the degree of a reduction in heterozygosity when compared to Hardy–Weinberg expectation...
, standard tools in population genetics. He was the chief developer of the mathematical theory
of
genetic driftGenetic drift or allelic drift is the change in the frequency of a gene variant in a population due to random sampling.The alleles in the offspring are a sample of those in the parents, and chance has a role in determining whether a given individual survives and reproduces...
, which is sometimes known as the Sewall Wright effect, cumulative stochastic changes in gene frequencies that arise from random births, deaths, and Mendelian segregations in reproduction. In this work he also introduced the concept of
effective population sizeIn population genetics, the concept of effective population size Ne was introduced by the American geneticist Sewall Wright, who wrote two landmark papers on it...
. Wright was convinced that the interaction of
genetic driftGenetic drift or allelic drift is the change in the frequency of a gene variant in a population due to random sampling.The alleles in the offspring are a sample of those in the parents, and chance has a role in determining whether a given individual survives and reproduces...
and the other evolutionary forces was important in the process of adaptation. He described the relationship between genotype or phenotype and
fitnessFitness is a central idea in evolutionary theory. It can be defined either with respect to a genotype or to a phenotype in a given environment...
as fitness surfaces or fitness landscapes. On
these landscapes mean population fitness was the height, plotted against horizontal axes representing the
allele frequenciesAllele frequency or Gene 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...
or the average phenotypes of the population.
Natural selectionNatural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....
would lead to a population climbing the nearest peak, while
genetic driftGenetic drift or allelic drift is the change in the frequency of a gene variant in a population due to random sampling.The alleles in the offspring are a sample of those in the parents, and chance has a role in determining whether a given individual survives and reproduces...
would cause random wandering.
Wright's explanation for stasis was that organisms come to occupy adaptive peaks. In order to evolve to another, higher peak, the species would first have to pass through a valley of maladaptive intermediate stages. This could happen by
genetic driftGenetic drift or allelic drift is the change in the frequency of a gene variant in a population due to random sampling.The alleles in the offspring are a sample of those in the parents, and chance has a role in determining whether a given individual survives and reproduces...
if the population is small enough. If a species was divided into small populations, some could find higher peaks. If there was some
gene flowIn population genetics, gene flow is the transfer of alleles of genes from one population to another.Migration into or out of a population may be responsible for a marked change in allele frequencies...
between the populations, these adaptations could spread to the rest of the species. This was Wright's
shifting balance theoryThe shifting balance theory of evolution is a view of evolution advocated by Sewall Wright that each of the four evolutionary forces is important to adaptive evolution...
of evolution. There has been much skepticism among evolutionary biologists as to whether these rather delicate conditions hold often in natural populations. Wright had a long standing and bitter debate about this with R. A. Fisher, who felt that most populations in nature were too large for these effects of genetic drift to be important.
Wright strongly influenced
Jay LushJay Laurence Lush was a pioneering animal geneticist who made important contributions to livestock breeding. He is sometimes known as the father of modern scientific animal breeding. Lush received National Medal of Science in 1968 and the Wolf Prize in 1979....
, who was the most influential figure in introducing
quantitative geneticsQuantitative genetics is the study of continuous traits and their underlying mechanisms. It is effectively an extension of simple Mendelian inheritance in that the combined effects of one or more genes and the environments in which they are expressed give rise to continuous distributions of...
into
animalAnimal breeding is a branch of animal science that addresses the evaluation of the genetic value of domestic livestock...
and
plant breedingPlant breeding is the art and science of changing the genetics of plants in order to produce desired characteristics. Plant breeding can be accomplished through many different techniques ranging from simply selecting plants with desirable characteristics for propagation, to more complex molecular...
. Wright's statistical method of path analysis, which he invented in 1921 and which was one of the first methods using a
graphical modelA graphical model is a probabilistic model for which a graph denotes the conditional independence structure between random variables. They are commonly used in probability theory, statistics—particularly Bayesian statistics—and machine learning....
, is still widely used in social science. He was a hugely influential reviewer of manuscripts, as one of the most frequent reviewers for Genetics. Such was his
reputation that he was often credited with reviews that he did not write.
From 1915 to 1925 Wright was employed by the Animal Husbandry Division of the U.S. Bureau of Animal Husbandry. His main project was to investigate the inbreeding that had occurred in the artificial selection that resulted in the leading breeds of livestock used in American beef production. He also performed experiments with 80,000 guinea pigs in the study of physiological genetics. Further more he analyzed characters of some 40,000 guinea pigs in 23 strains of brother-sister matings against a random-bred stock. (Wright 1922a-c). The concentrated study of these two groups of mammals eventually led to the Shifting Balance Theory and the concept of "surfaces of selective value" in 1932. (Wright 1988 Pg 122 American Naturalist)
He did major work on the genetics of guinea pigs, and many of his students became influential in the development of mammalian genetics. He appreciated as early as 1917 that genes acted by controlling
enzymeEnzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
s.
An anecdote about Wright, disclaimed by Wright himself, describes a lecture during which Wright tucked an unruly guinea pig under his armpit, where he usually held a chalkboard eraser: according to the anecdote, at the conclusion of the lecture, Wright absent-mindedly began to erase the blackboard using the guinea pig.
Wright and philosophy
Wright was one of the few geneticists of his time to venture into
philosophyPhilosophy is the study of general and fundamental problems, such as those connected with existence, knowledge, values, reason, mind, and language. Philosophy is distinguished from other ways of addressing such problems by its critical, generally systematic approach and its reliance on rational...
. He found a union of concept in
Charles HartshorneCharles Hartshorne was a prominent American philosopher who concentrated primarily on the philosophy of religion and metaphysics. He developed the neoclassical idea of God and produced a modal proof of the existence of God that was a development of St. Anselm's Ontological Argument...
, who became a lifelong friend and philosophical collaborator. Wright believed that the birth of the consciousness was not due to a mysterious property of increasing complexity, but rather an inherent property, therefore implying these properties were in the most elementary particles.
Legacy
Wright and Fisher, along with J.B.S. Haldane, were the key figures in the modern synthesis that brought genetics and evolution together. Their work was essential to the contributions of
DobzhanskyTheodosius Grygorovych Dobzhansky ForMemRS was a prominent geneticist and evolutionary biologist, and a central figure in the field of evolutionary biology for his work in shaping the unifying modern evolutionary synthesis...
,
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...
,
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...
,
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...
, and
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...
. The modern synthesis was the most important development in evolutionary biology after
DarwinCharles Robert Darwin FRS was an English naturalist. He established that all species of life have descended over time from common ancestry, and proposed the scientific theory that this branching pattern of evolution resulted from a process that he called natural selection.He published his theory...
. Wright also had a major effect on the development of mammalian genetics and biochemical genetics.
An interesting anecdote about Sewall Wright and
Barbara McClintockBarbara McClintock , the 1983 Nobel Laureate in Physiology or Medicine, was an American scientist and one of the world's most distinguished cytogeneticists. McClintock received her PhD in botany from Cornell University in 1927, where she was a leader in the development of maize cytogenetics...
.
External links