Sewall Wright for dunces

Sewall Wright for dunces

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[This is one more post in my growing "X for dummies/idiots/morons/etc." series.]

I've been enjoying Provine's The origins of theoretical population genetics for the last couple of days, but I must confess that I find his description (on pp 127-8) of the logic behind Sewall Wright's (and W. Castle's) selection experiments with "hooded rats" about as clear as if it had been chiseled in Linear A…

Which is really bumming me out, because I'd love to understand these experiments.

Does anyone know where I can find a description of these experiments aimed at those with only a very limited grasp of classical genetics? (I took a graduate-level genetics class a billion years ago, and I did not find it easy.)

I think there might be several places to read a description of these experiments, but they are discussed extensively in a book by historian-philosopher Lindley Darden, entitled "Theory Change in Science: Strategies from Mendelian Genetics", parts of which are available online. See p. 112 of Darden's book for references to other accounts of these experiments by historians E.A. Carlson (1966) and W. Provine (1988).

Everyone knows what Castle did but his aims have been obscured by "Synthesis Historiography" (i.e. making things turn out right for Ernst Mayr and his homies).

What Castle did was to breed rats in the laboratory and implement selection on coat patterns, with such success that he has able to get a large seemingly continuous range of forms. Imagine breeding oreos, with one line of selection of darker forms, and one of lighter, and achieving the success of getting both pure-black or pure-white oreos, and then lining up all the oreos from black to white to show the continuous range of forms.

The story that we hear from people like Wright and Provine is that this proved that selection can work on continuous variation, an idea that the "mutationists" allegedly rejected, paving the way for acceptance of Darwinism.

Yet, while the experiments may have helped one version of Darwinism, they also represented the dying gasps of another form of Darwinism-- the form that Darwin proposed and Castle was (partially) defending.

You can get an inkling of this from p. 143 of Provine's book, where you will find a curious confession, made in passing. Provine is explaining why Pearson did not want to publish Fisher's famous 1918 paper. He writes "Pearson claimed, and Darwin would probably have agreed, that the continuous variations in a pure line were heritable and that continued selection in a pure line should be effective."

Why would Pearson believe-- 17 years after the rediscovery of Mendelian inheritance-- that the environmental variations in Johannsen's pure lines were suitable material for selection? The reason is that this is what Darwin believed, and Pearson was a follower of Darwin. Darwin's "indefinite variability", the fuel for modification in his theory of "natural selection", described in Ch. 1 of the OOS, is clearly a description of environmental variation-- it is always present and emerges anew every generation in response to "conditions of life" (see Winther, 2000). Darwin knew about "definite" single variations or "sports", which could be inherited perfectly (whereas indefinite variations were inherited by blending), but he didn't think they were important for evolution. Darwin bet on the wrong horse, as Johannsen showed in 1903.

Pearson, Castle, and others defended Darwin's original view well into the 20th century. They were not satisfied with the idea that selection merely sorted out stable Mendelian factors that undergo rare mutations. Instead, they held out hope that there was some other form of heredity, or that the Mendelian units were squishy and underwent continuous shifts in potency under conditions of selection. Thus Castle and Phillips in 1914 argued that "the unit character for hooded pattern is itself variable"

Muller, Sturtevant and others from Morgan's lab disagreed, arguing instead that there were simply various Mendelian modifying factors in the background affecting coat color. There was a long-running dispute over the proper genetic interpretation of Castle's results. If you want a very clear statement of the dispute, go to a 1916 article by Jennings, p. 287:

"Castle finds that in rats he can, by selection, gradually increase of decrease the amount of colour in the coat, passing by continuous stages from one extreme to the other. As to this, he holds two main points:

  1. The change is an actual change in the hereditary characteristics of the stock; not a mere result of the recombination of Mendelian factors. This is the general and fundamental point at issue.

  2. More specifically, he holds it to be an actual change in a single unit factor; this single factor changes its grade in a continuous and quantitative manner.

On the other side, the critics of these views maintain that the changes shown are not actual alterations in the hereditary constitution at all, but are mere results of recombinations of Mendelian factors. And specifically, they find a complete explanation of such results as those of Castle in the hypothesis of multiple modifying factors."

A few years later in 1919, Castle recanted his earlier view and accepted the multifactorial theory (the development of which is described by Kyung-Man Kim, cited below).

And finally, the idea that the "mutationists" rejected selection on quantitative variation is mistaken. What the mutationists rejected was selection on non-heritable environmental variations. Johannsen's 1903 results were revolutionary because scientists at the time understood that they refuted Darwin's theory. We don't "get" this today because "Darwinism" has been redefined to disentangle "natural selection" from Darwin's errant views of heredity-- see Jean Gayon's "Darwinism's Struggle for Survival" for more explanation.


Kim K-M. 1994. Explaining scientific consensus : the case of Mendelian genetics New York: Guilford Press. xxiv, 239 p. p.

Gayon J. 1998. Darwinism's Struggle for Survival: Heredity andthe Hypothesis of Natural Selection Cambridge, UK: Cambridge University Press.

Winther RG. 2000. Darwin on Variation and Heredity. Journal of the History of Biology 33:425-55.

I don't have access to Provine's book, and I can't describe the details of the hooded rat experiments, but here is an attempt to explain the importance of the work.

Darwin published “Origin of Species” in 1859. He proposed that modern species were all descended from ancestral species, and that evolution proceeded by natural selection. He believed that evolution proceeded gradually by an accretion of small changes (gradualism). The origins of hereditary change were, of course, unknown to Darwin.

Mendel's work (published in 1865) was rediscovered in 1900, and gave rise to a school of thought referred to as mutationism. Mutationist theories emphasised the importance of single factor changes with large effects, and placed these “leaps forward” at the centre of the mechanism for the generation of new species. This was in contrast to the biometricians who argued, in the Darwinian tradition, that natural selection acted on populations in which there was continuous variation. Extreme mutationists believed that continuous variation within a species had no relevance to the evolution of new species. Their view was that within a species most genes were fixed (100% wild-type allele), and that only mutations could create new species ('hopeful monsters'). T.H. Morgan, for example, was a strong proponent of the mutationist theory, so this wasn't some minor controversy.

Sewall Wright joined the laboratory of W.E.Castle as an assistant in 1912, when he was 23. Starting with black and white hooded rats (white rats with black 'hoods') they instigated breeding programmes and showed that they could progress gradually, through a number of generations, towards all white or all black rats. The importance of this work was that it demonstrated that there was underlying genetic variation within this strain of rats that could be acted upon by selection (selective breeding) resulting in gradual changes in coat colour. This provided strong evidence for the gradualist school.

By the 1930s the modern synthesis began to emerge, which combined mutationist and gradualist ideas: natural selection acts upon populations (gene frequencies etc.) but mutation provides the raw material that creates new variations in the population. Key to the acceptance of the modern synthesis was the development of a mathematical treatment of population genetics. This led to the current view of phenotypic traits influenced by multiple loci, with natural populations harbouring genetic variability which can be acted upon by selective forces. We have all accepted this and so of course it is difficult to think ourselves into the controversies that existed in genetics at the beginning of the twentieth century.

Here is an article in which Sewall Wright refers briefly to his work with Castle, placing it in historical context. It also describes subsequent work with guinea pigs. This is a quotation from the article which underscores what I have written:

From assisting Prof. Castle, I learned at firsthand the efficacy of mass selection in changing permanently a character subject merely to quantitative variability. Because of this and a distaste for miracles in science, I started with full acceptance of Darwin's contention that evolution depends mainly on quantitative variability rather than on favorable major mutations. Thus, I have assumed that species are typically heteroallelic in tens of thousands of loci in which the leading alleles differ only slightly in effect, a situation that is maintained in a continually shifting state of near-equilibrium by the opposing pressures of recurrent mutation, diffusion and weak selection. Only a few loci at any time can show fairly rapid changes in allelic frequencies from strong selection.

Sewall Wright Effect

According to genetic drift, in small, non-randomly mating populations gene frequencies are found to fluctuate purely by chance. Smaller the population, larger will be the fluctuation in gene frequency.

Genetic drift works on the principle of tossing of a coin. If a coin is tossed, then chances of getting heads and tail would be equal only if it is tossed for a large number of times, so that the standard error is low. But if the coin is tossed only few times, then standard error will go up and you may get head or tail any number of time.

Standard Error = square root of Pxq/n, where P=frequency of dominant gene (or head of a coin), q=frequency of recessive gene (or tail of a coin) and n=number of individuals in a population (or number of times the coin is tossed).

For example, let us imagine a small population of black hamsters say only one pair, one MMand the other mutant Mm. If they can produce only 2 offspring, then the chance that the first offspring will be MMis 0.5 and that the second offspring will also be MMis also 0.5. The chance that both offspring will be MMis reduced to 0.5ࡦ.5=0.25. In such a case the mutation m will be lost forever. Similarly, by chance both offspring can be Mm, in which case the mutation mwill have a chance to express in the next generation. Thus the population may drift towards losing or fixing a mutation purely by chance. Gene frequency will continue to fluctuate until one allele is lost and the other fixed.

Extinction of certain species, which are left with small populations, is known to be due to genetic drift, when lethal mutations are fixed, e.g. passenger pigeon and cheetah became extinct due to genetic drift that fixed lethal mutations. Carnivores usually have small populations and are affected by genetic drift. Human tribes that marry within their own communities also face genetic drift and accumulate lethal mutations.

Founders effect & Bottleneck effect: When a small population migrates to a new area, the frequency of genes is determined by the genetic drift (Mayr, 1963 Sheppard, 1960). For example, American Indians have no ‘B’ group in their blood. However, in Asia, which is the ancestral home of American Indians, ‘B’ group is widespread. The ancestral population of mongoloids that migrated across Bering strait to North America might have been very small and must be having all kinds of blood groups, but due to genetic drift, ‘O’ group has been fixed and ‘B’ group eliminated purely by chance.

Bottleneck effect is a phenomenon found in animals that follow seasonal cycle of dormancy and activity, such as insects, amphibians and a large number of invertebrates. During breeding season their populations are very large but as the adverse climate arrives majority of individuals are killed and very few manage to find protective shelters and undergo diapause to tide over adverse period. This small population then produces next generation by way of genetic drift.

Susan C. Alberts

The Sewall Wright Award, established in 1991 and now in its 30th year, is given annually to honor relatively senior but still active investigators who are making fundamental contributions to the Society's goals, namely promoting the conceptual unification of the biological sciences.

The 2020 Sewall Wright Award recognizes Susan C. Alberts, currently the Robert F. Durden Professor in the Departments of Biology and Evolutionary Anthropology, Duke University in Durham, North Carolina. Susan is a lifetime member of the American Society of Naturalists, a member of the National Academy of Sciences, fellow of the American Academy of Arts and Sciences, American Association for the Advancement of Science, Animal Behavior Society, and the Bass Society of Duke University, and has received several other awards in recognition of her work. She will be the President of the Animal Behavior Society for the next four years.

Particularly noteworthy are discoveries by Susan and colleagues at the interface of animal behavior, evolutionary biology, and anthropology, uncovering links between social behaviors (dominance, mating systems, group identity, kin recognition), genetic relatedness and lifetime reproductive success. Most of Susan&rsquos studies have been on baboons and elephants, conducted with the Amboseli Baboon Research Project in Kenya. Her work features longitudinal empirical data gathered over decades of painstaking fieldwork, measuring behaviors and reproduction of known individuals across their lifespans in the same populations experiencing long-term demographic and environmental changes. Most of the data are available online in the BABASE archive that Susan helps to curate. These kinds of studies are rare indeed, and result in a rich unifying blend of data, methods, and theory that cannot be adequately described in a few short paragraphs. Three areas stand out.

The molecular ecology and genetics of behavior: Susan helped pioneer the application of molecular genetic data in studies of behavioral ecology. Susan co-led some of the first studies demonstrating that male mating behavior predicted genetic paternity in wild primates. For instance, despite female baboons mating with multiple males, the males participate in paternal care (e.g., recognize their offspring and intervene on their behalf during conflicts), paternal relatives recognize each other and avoid inbreeding, and female offspring mature more quickly when fathers are present and attentive.

Fitness consequences of female social relationships: With the expectation that forming strong and stable social bonds in mammals should increase fitness, Susan&rsquos 2003 Science paper co-authored with Joan Silk and Jeanne Altmann provided some of the first direct empirical evidence for this idea. Using 15 years of data describing female baboons&rsquo sociality they showed that those with the strongest social bonds with adults of both sexes had the highest longevity and offspring survival. Subsequent studies revealed persistence and reciprocity of female-female bonds - a basic assumption underlying theoretical explanations for altruism that has rarely been confirmed in wild social mammals. Susan's pioneering work in this area inspires others to follow in her footsteps in understanding how sociality contributes to fitness, especially through lifespan.

Comparative primate life histories: More recently Susan has directed research toward understanding patterns of aging in primates, working in collaboration with the Primate Life History Database working group. The studies again harness the power of long term field studies of primates, including humans. First, Susan led work showing that patterns of aging, particularly that males age faster and have shorter lifespans, appear in all three major primate lineages. By contrast, human women appear to be unique among primates by undergoing early reproductive senescence (i.e., menopause). However&mdashagain elegantly showcasing the value of longitudinal studies&mdash when lifespans with lower variability are also longer in both humans and other primates, suggesting that patterns of aging in humans have deep evolutionary roots. This study won the 2016 Cozzarelli Prize from the National Academy of Sciences for behavioral and social sciences.

Susan is a highly productive and innovative scientist, co-publishing with many collaborators. She is also a generous and kind mentor to her own graduate student and post-doctoral trainees and to the many researchers working at Amboseli. She has been recognized as an effective teacher. Susan continues to have an outsized effect on the fields of animal behavior and evolutionary anthropology, setting the agenda for some of the most exciting conceptual and empirical work on the evolution of social behavior and life histories.

Michael F. Antolin, Chair, on behalf of the Sewall Wright Award Committee: Ellen Ketterson, Mark Urban

Wright, Sewall (1889-1988)

The Life of Sewall Wright

Sewall Green Wright was born to Philip Green and Elizabeth Quincy Sewall Wright, residents of Melrose Massachusetts, on December 21, 1889. The family moved three years later after Philip accepted a teaching job at Lombard College, a Universalist college in Galesburg, Illinois. The ancestry of the Wright family could be traced through 16th century England to the 7th century reign of Charlemagne, and many of Sewall’s ancestors were distinguished educated and innovative individuals. Wright would later profess a great interest in heredity in the example of his life, he certainly manifested the genes of past success.

Wright and his brothers, Quincy and Theodore Paul, were very gifted children. Although they did not initially attend official schools, they were reading and writing at unusually early ages. Sewall entered the “publishing” arena at the age of seven with his pamphlet on various animals’ physical characteristics. Also, he was then able to extract cube roots, to the disgust of the other children. The atmosphere at the school was not conducive to learning, and Wright had to avoid participation for fear of sparking the ire of the other boys with his knowledge.

Sewall during his student days at Lombard College.

From his youth, Wright was fascinated with math and mathematical models. He would often waste afternoons playing with his mother’s balance in the kitchen, and she would in turn teach him arithmetical methods. The Wright parents were fond of reading to their children, and in the home a highly intellectual atmosphere was continually fostered. Wright, however, did not want to follow his father’s suggestions to study poetry he instead was enthralled by nature. Wright attended Galesburg High School, graduating in 1906 to enroll in Lombard College to concentrate on mathematics and surveying.

At the College, Sewall Wright’s interest in biology was spurred by Professor Wilhelmine Entemann Key, one of the first women to earn a Ph.D from the University of Chicago. This interest led Wright to study at Cold Spring Harbor during the summers of 1911 and 1912, after which he entered the University of Illinois for graduate work in biology. After graduating with a Master’s degree in 1912. he accepted an opportunity to work with Ernest William Castle of Harvard’s Bussey Institution. The research would concentrate on mammalian genetics, particularly as exhibited in guinea pigs.

For his Ph.D, he investigated the inheritance of coat colors in the animals, received the degree in 1915, and went on to work on animal husbandry for the U.S. Department of Agriculture in Washington, D.C, where his task was to improve livestock. Wright suggested, producing via inbreeding to promote genetic dominance over fringe traits. “Systems of Matings,” published in 1921, was the culmination of mathematical work on selection and breeding. Eventually, he would continue this line of investigation in studying population demographics.

Wright (second from the left in front row) at Cornell University in 1922. Courtesy of the Archives of the Department of Plant Breeding at Cornell University.

Wright decided to return to the work that he loved best, and joined the faculty of the University of Chicago to teach and research genetics. He embarked upon a distinguished career of publication at the university level, writing on genetics in populations and path analyses that could be applied to mathematical and social scientific models. Wright’s achievements in these areas were groundbreaking.

As a statistician, Wright began work in 1917 with covariant analyses to determine the importance of various factors in defining traits. This expertise was extended into animal breeding. Mammalian genetics was one of his main interests. At the Bussey Institution, he was concerned with studies of rats, guinea pigs, and rabbits. Wright published on color inheritance in 1917 and 1918, the year in which he pioneered path analyses in his study of body characteristics in animals.

On evolution, Sewall Wright was surely one of the most renowned researchers of the century. Wright developed a theory that attributed a substantial amount of genetic variance or “creativity” to small genetic fluctuations among small population groups. This was an innovative idea and caused the well-documented debate with the Englishman R.A. Fisher, who insisted that variance could be analyzed only in relation to large populations. Wright specialized in this field of population genetics while a professor at the University of Chicago.

Department of Zoology faculty, circa 1945. Wright is the second from the left in the bottom row.

One of Wright’s peculiar interests was in inbreeding, perhaps because his parents were in fact first cousins. His extensive guinea pig crosses were also notable.

Upon mandatory retirement from the University of Chicago in 1955 at the age of 65, Wright entered the University of Wisconsin, and became the Leon J. Cole Professor of Genetics for 5 years. As a secondary interest, Wright also engaged in philosophy. On the philosophy of science, he expressed to the American Society of Naturalists in 1952, “It is the task of science, as a collective human undertaking, to describe from the external side, such statistical regularity as there is in a world in which every event has a unique aspect, and to indicate where possible the limits of such description. It is not a part of its task to make imaginative interpretations of the internal aspect of reality. The only qualification is in the field of introspective psychology in which each human being is both observer and observed, and regularities may be established by comparing notes.”

Wright was known to be shy and unassuming but intense in academic matters. James Crow of the University of Wisconsin’s Genetics Department traveled to Chicago with a student of his to ask Wright some questions on genetic experiments. Wright disappointed the men when he responded to each question that he was “unable to answer” it. The men left disillusioned, only to find that Wright had researched each question, and had written a 14- page response attending to every possible intricacy of each question. Professor Millard Sussman, who was the dean of the University of Wisconsin Medical School, offered that Wright was “a remarkable man . who lived his entire life for population genetics and related areas of research.”

Maruyama, Louise Wright, Sewall Wright, Kimura, Ohta, and an unidentified woman at the Mishima Experimental Station at the time of the International Conference of Genetics in Japan in 1968.

In evolutionary biology Wright created a particularly outstanding work, Evolution and the Genetics of Populations, in four parts, of which the final volume was released in 1978 when he was 98 and he was “retired. ” Among the numerous awards and honorary degrees received by Wright were the Balzan Prize (1984), Medal of the Royal Society of London (1980), the National Medal of Science (1966), the Weldon Medal of the Royal Society of London (1947), the Elliott and Kimber Awards from the National Academy of Sciences (1947 and 1956), and the Lewis Prize from the American Philosophical Society. Wright’s biographer, William Provine, predicted that “historians and biologists in the 21st century will look upon Wright as perhaps the single most influential evolutionary theorist of this century.”

Sewall Wright married Louise Williams, a genetics teacher at Smith College, in 1921, and they had three children Elizabeth Rose, Richard, and Robert. He was a Unitarian, and attended church in Madison during the years when the minister was Max Gaebler.

Sewall Wright died on March 3, 1988, at the age of 99, after a long and very productive life.

— by Edric Lescouflair, a student of Sewall Wright.

The Career of Sewall Wright

by James F. Crow, Professor Emeritus of Genetics and Medical Genetics, University of Wisconsin

Sewall Wright’s untimely death occurred after complications from a fractured pelvis, the result of his slipping on an icy spot during one of his daily long walks. It may seem strange to regard a death in his 99th year as untimely, but not for Wright. He was eagerly looking forward to participating in this summer’s International Congress of Genetics in Toronto and enjoying banter about what to do in his second century. Only a few hours before his death he was discussing his most recent paper, wondering whether his reprints had arrived, signing a check for the coming month’s rent, and wondering how he could handle his income tax from the hospital. Yet in many ways a sudden death was a blessing. A long confining illness would have been very hard for one accustomed, as he was, to a high level of physical and mental activity. Walking and, when possible, swimming were very important to him, and he couldn’t read in a hospital bed.

Wright’s death marks the end of an era. He had been for many years the sole survivor among those who established genetics as a solid science starting about 1915, a group that included Muller, Stadler, Sturtevant, Bridges, Fisher, and Haldane. With the latter two he founded the subject of population genetics and gave natural and artificial selection a quantitative basis.

Sewall holding a baby raccoon at the Provine Farm in New York. Photo by Doris Marie Provine.

Wright’s life and work are abundantly documented. There is a full-length biography, a reprinting of 42 of his 212 and several shorter articles. Provine has taped more than 120 hours of interviews and has preserved virtually all of Wright’s voluminous correspondence. There is also an oral history. Future historians will have a plethora of material. Because so much has been written about his professional life, and much more will be, I have elected to give a more personal account of this amazing man.

Wright’s first paper was published in 1912 and his last in 1988, a span of 76 years. Wright’s four volume series was written in his late 70s and 80s. His last paper appeared in the January, 1988 issue of the American Naturalist. He retained his intellectual vigor until the end. Although his eyesight deteriorated badly, he learned to read with a machine that projected the printed page onto a television screen. He always liked history and biography, but only in his later years did he have the leisure to indulge this interest. In his last few weeks he read biographies of Jefferson, Tchaikovsky, Einstein, and the Kennedys and Fitzgeralds. And he could discuss them in detail. He was dissatisfied with the Einstein biography, and asked for a book with less personal life and more relativity.

Wright’s intellectual life extended far beyond the normal range in both directions. He was also a precocious child. At age seven, before starting school, he wrote a pamphlet entitled “The Wonders of Nature” which still exists. It included sections about constellations, squashes, ants, dinosaurs, bees, marmosets, and the story of a wren that could not be dissuaded from nesting in the family mailbox. His report on the chicken gizzard is typical: “Have you ever examined the gizzard of a fowl? The gizzard of a fowl is a deep red color with blue at the top. First on the outside is a very thick muscle. Under this is a white and fleecy layer. Holding very tight to the other. I expect you know that chickens eat sand. The next two layers are rough and rumply. These layers hold the sand. They grind the food. One night when we had company we had chicken pie. Our Aunt Polly cut open the gizzard, and in it we found a lot of grain, and some corn.”

Philip Wright, Sewall’s father, was a polymath and was on the faculty of tiny Lombard College in Galesburg, Illinois. He taught mathematics, astronomy, surveying, economics, physical education, and English composition. He loved poetry and music and was disappointed that Sewall did not take to them. He had a printing press on which he printed his poems, as well as the College bulletins. Sewall and his brothers, Quincy and Theodore, printed the first poems of Carl Sandburg, who was a student in their father’s composition class. Philip Wright later moved to Harvard and the Brookings Institution where he published a number of books on economics. One of them, The Tariff on Animal and Vegetable Oils, included an appendix by Sewall Quincy went on to become a distinguished scholar in the field of international law, while Theodore was chief engineer at Curtis-Wright, a Civil Aeronautics commissioner, and acting president of Cornell University. He is said to have turned down the presidency because he didn’t like raising money.

Sewall Wright was born December 21, 1889, in Melrose, Massachusetts, but grew up in Galesburg, Illinois, where he attended Lombard College. He learned about the subject of genetics by reading Punnett’s account of Mendelism in the Encyclopedia Brittanica. Although biologists regard Wright as a formidable mathematician, he never took any advanced courses his math, beyond what he learned from his father, was self-taught.

A photo-sketch of Wright by Edward Schumann.

Between his third and fourth years of college, he made use of his surveying and mathematical skills by working with a crew surveying for a railroad line in the Standing Rock Reservation in South Dakota. It was an exciting time for him, in the Old West tradition with cowboys, Indians, mule skinners and outlaws and he loved to tell about it. Late in the year he developed a lung infection and had to stay in a caboose. He was not too ill, however, to climb on the roof to see Halley’s comet. While confined to the caboose, he read Tait’s (1890) book on Quaternions. After his death I found what must be the same book, with many of the problems checked, these presumably being the ones that he had worked. It appears that he got about half way through the book. Curiously, J. B. S. Haldane also read Tait’s book on Quaternions under strikingly similar circumstances—while recovering from wounds in World War I. As far as I know, neither of them made use of this technique in his later work. One consequence of Wright’s lung infection was that he was refused life insurance by New England Mutual, something he found increasingly amusing as his age advanced far beyond the usual life expectancy.

Upon graduation from Lombard, he received a fellowship at the University of Illinois. During this year William Castle visited the campus and, after an interview with Wright, hired him on the spot as an assistant. Wright’s Ph.D. from Harvard came in 1915. His thesis was on coat colors in guinea pigs, but he also worked out ways to measure inbreeding during this time.

From 1915 to 1925 he was senior animal husbandman in the United States Department of Agriculture. During this period he did his classical studies on inbreeding and factor interaction in guinea pigs, the analysis of livestock breeds, and the method of path analysis. The last was a novel method for interpreting correlations in complex causal systems. His original paper on path analysis, “Correlation and Causation,” was rejected by the Bureau of Animal Industry, but was later published, thanks to the intercession of his colleague G. N. Collins, a leading maize geneticist. Wright also had trouble with the publication of his monumental analysis of corn and hog correlations. It was rejected by the officials in the Department of Agriculture on the grounds that an animal husbandman had no business writing about economics. Henry Wallace, later to become Vice President, eventually learned of the paper and, through the influence of his father, then Secretary of Agriculture, arranged for its publication. This may well have been the zenith of the Harding administration.

In 1926 Wright moved to the University of Chicago where he continued his guinea pig studies and wrote his influential papers on evolutionary theory. There he had several graduate students who went on to distinguished careers. Curiously, only one did a thesis in population genetics and none in mathematical theory Wright’s emphasis at the time was on developmental and physiological genetics. At age 65 he retired from Chicago and was for 5 years Professor at the University of Wisconsin. Frugal Wisconsin never paid him a full salary, only a supplement to his Chicago retirement annuity. For this, the University got more than 30 years of Wright quality work—surely the best bargain Wisconsin ever had.

An aspect of Wright’s life that is not fully appreciated was his great service to others. While at the United States Department of Agriculture he answered, fully and conscientiously, numerous letters from farmers and breeders. He had heavy teaching responsibilities at the University of Chicago, often two courses in the same term. His lectures were always carefully prepared, and he was in the labs himself.

He was often called on to review manuscripts, difficult ones especially. He was one of the most frequent reviewers for Genetics. Many a published paper is better for Wright’s attention. Once, as an anonymous reviewer, he spent an enormous amount of time re-analyzing the data in a paper on mouse genetics, and reached the opposite conclusion. The author simply rewrote the conclusion. Wright’s reputation as a reviewer was so great that he was sometimes credited with reviews he didn’t write.

Base camp. Wright is second from left.

Wright was quiet, shy, introverted, and uneasy with small talk. He liked to talk, but only when there was substance. Conversations were often strained until the right button was pressed then he was off on what was typically a long monologue. He liked to talk about his ancestors (for example, Judge Samuel Sewall, of Salem witchcraft fame), the connections between some of these ancestors and characters in Shakespeare’s historical plays, his childhood, his days on the railroad surveying crew, his travels, his guinea pigs, and, of course, his theory of evolution. All who heard him as a lecturer and teacher have vivid, affectionate memories of his crowding an enormous amount of factual information into a lecture his talking and writing at breakneck speed his note-cards, illegible to all but him his covering the blackboard with symbols and his clothes with chalk, and erasing the board with any object at hand (although he denied the story of his using a guinea pig for this purpose) and, above all, his invariably running overtime. His wife Louise repeatedly reminded him to confine his lecture to the allotted time. He duly promised, but simply found it impossible to omit details.

Wright has had an abundance of medals, prizes and awards, essentially all for which a population geneticist is eligible. He has had a number of honorary degrees although, as he liked to say, far fewer than Herbert Hoover. He has been president of the Genetics Society of America, the American Society of Zoologists, the Society of Naturalists, the Society for the Study of Evolution, and the Tenth International Congress of Genetics. To mention one more, he was the only geneticist ever to be elected a fellow of the Econometric Society. He method of path analysis, which uses correlations to analyze complex interrelationships in nonexperimental data, has recently become de rigueur in some social sciences. At Wright’s 90th birthday banquet a Wisconsin sociologist said that Wright’s contributions were such that the Sociology Department was prepared to offer him an assistant professorship.

Wright married Louise Williams, who, in contrast to her husband, was an easy conversationalist and made friends readily. She especially liked to travel, and encouraged him to take long automobile trips which they both enjoyed. She died in 1975 leaving him very lonely, although this was not apparent he was not one to share such feelings with others.

My favorite anecdote epitomizes this modest, unselfish man with his self-deprecating wit that I want to repeat it. While writing his books he received a modest stipend from the National Science Foundation and during this time the Foundation offered to provide an inflationary adjustment to his pay. He was in his late 80s at the time. When I brought him this good news, he replied that, according to his careful calculations, his productivity was declining at exactly the same rate as the value of the dollar and he didn’t deserve any salary increase. He never accepted it.

— By James F. Crow, a colleague of Sewall Wright. Abridged from Genetics 199, May 1988. Courtesy of the Genetics Society of America.

The Philosophy of Sewall Wright

Very few geneticists have written seriously about philosophy. Wright is an exception. He discovered that his Chicago colleague, Charles Hartshorne, shared a similar view about the philosophy of organism, and they became lifelong friends.

The philosophy is in the tradition of Leibniz. Wright’s view is that there is no material basis for a mysterious “emergence” of new properties as systems become more complex. This being the case, one is forced to assume that such properties as consciousness must necessarily reside in the most elementary particles. He has developed this view in several papers a good example is his presidential address to the American Society of Naturalists, published in 1953 under the title “Gene and Organism.”

Wright’s philosophical view has attracted some attention among philosophers, and he has several times been invited to participate in national and international conferences. It has not received any significant attention from biologists. Wright found it amusing that his views of the biological organism got more notice from philosophers than from his fellow biologists. His teacher, Wilhelmina Key, wrote him after receiving a reprint of his presidential address that at last he had written a paper that she could understand.

From “Sewall Wright, the Scientist and the Man,” Perspectives in Biology and Medicine, 25, 2 Winter 1982.

Sharon Strauss

The Sewall Wright Award, established in 1991, is given annually and honors a senior but still active investigator who is making fundamental contributions to the Society's goals, namely, promoting the conceptual unification of the biological sciences.

The 2019 Sewall Wright Award honors Sharon Y Strauss, Professor in the Department of Evolution and Ecology at the University of California, Davis. Sharon has had a career-spanning association with the American Society of Naturalists, from being a Jasper Loftus-Hills Young Investigator in 1990 to President of the Society in 2018. Sharon is a fellow of the California Academy of Sciences, the American Academy of Arts and Sciences, and the Ecological Society of America.

Sharon is known for the breadth of her research and writings in ecology and evolutionary biology, with a focus on plants. Beginning with early work on plant interactions with herbivores, her work expanded to include interactions with mutualists (pollinators, microbes) and antagonists (herbivores, parasites). She argued early on that multi-species interactions, and indirect interactions, in particular, are important in shaping the dynamics, distribution and evolution of plant populations.

Sharon was an early proponent of integrating ecological and evolutionary research, before &ldquoeco-evolutionary dynamics&rdquo was a buzzword. She showed how species interactions shape patterns of natural selection on plants, e.g., how invasive species affect the ecological and evolutionary responses of natives. Her work also illustrates how trait evolution can shape the outcome of species interactions, and how eco-evolutionary feedbacks maintain both genetic and species diversity in plant communities. In the past decade, the evolutionary lens of her work has expanded to consider phylogenetic and macro-evolutionary influences on species interactions, coexistence, and geographic distributions.

Sharon&rsquos work embodies the Society&rsquos mission of introducing new subjects and advancing conceptual unification across disciplines. She has published ground-breaking empirical studies and authored or co-authored an impressive number of &ldquoideas&rdquo papers in leading journals such as Trends in Ecology and Evolution and Annual Review of Ecology, Evolution and Systematics. Sharon has also been an important mentor to a large cadre of graduate students and postdocs whose work is now shaping advances in basic and applied ecology and evolutionary biology.


We evaluate Sewall Wright's three-phase "shifting balance" theory of evolution, examining both the theoretical issues and the relevant data from nature and the laboratory. We conclude that while phases I and II of Wright's theory (the movement of populations from one "adaptive peak" to another via drift and selection) can occur under some conditions, genetic drift is often unnecessary for movement between peaks. Phase III of the shifting balance, in which adaptations spread from particular populations to the entire species, faces two major theoretical obstacles: (1) unlike adaptations favored by simple directional selection, adaptations whose fixation requires some genetic drift are often prevented from spreading by barriers to gene flow and (2) it is difficult to assemble complex adaptations whose constituent parts arise via peak shifts in different demes. Our review of the data from nature shows that although there is some evidence for individual phases of the shifting balance process, there are few empirical observations explained better by Wright's three-phase mechanism than by simple mass selection. Similarly, artificial selection experiments fail to show that selection in subdivided populations produces greater response than does mass selection in large populations. The complexity of the shifting balance process and the difficulty of establishing that adaptive valleys have been crossed by genetic drift make it impossible to test Wright's claim that adaptations commonly originate by this process. In view of these problems, it seems unreasonable to consider the shifting balance process as an important explanation for the evolution of adaptations.

Keywords: Adaptation genetic drift natural selection peak shift population structure shifting balance.

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THIS IS PERHAPS THE BEST BIOGRAPHY EVER WRITTEN OF A SCIENTIST--BENTLEY GLASS. 9 1/4 inches tall softcover, color printed laminated covers, 545 pages, fine. SEWALL WRIGHT (1889 - 1988) was an American geneticist known for his influential work on evolutionary theory and also for his work on path analysis. He was a founder of population genetics alongside Ronald Fisher and J.B.S. Haldane, which was a major step in the development of the modern synthesis combining genetics with evolution. He discovered the inbreeding coefficient and methods of computing it in pedigree animals. He extended this work to populations, computing the amount of inbreeding between members of populations as a result of random genetic drift, and along with Fisher he pioneered methods for computing the distribution of gene frequencies among populations as a result of the interaction of natural selection, mutation, migration and genetic drift. Wright also made major contributions to mammalian and biochemical genetics. WILLIAM B. PROVINE (1942 - 2015) was an American historian of science and of evolutionary biology and population genetics. He was the Andrew H. and James S. Tisch Distinguished University Professor at Cornell University and was a professor in the Departments of History, Science and Technology Studies, and Ecology and Evolutionary Biology.

Title: Sewall Wright and Evolutionary Biology

Location Published: Chicago and London, The University of Chicago Press: 1989

Customer Reviews

"Provine's thorough and thoroughly admirable examination of Wright's life and influence, which is accompanied by a very useful collection of Wright's papers on evolution, is the best we have for any recent figure in evolutionary biology."
&ndash Joe Felsenstein, Nature

"In Sewall Wright and Evolutionary Biology [. ] Provine has produced an intellectual biography which serves to chart in considerable detail both the life and work of one man and the history of evolutionary theory in the middle half of this century. Provine is admirably suited to his task [. ] The resulting book is clearly a labour of love which will be of great interest to those who have a mature interest in the history of evolutionary theory."
&ndash John Durant, Times Higher Education Supplement

The role of illness beliefs and coping in the adjustment to dentine hypersensitivity

Jenny M. Porritt , . Sarah R. Baker , in Dentine Hypersensitivity , 2015


Structural equation modeling (SEM) using AMOS 18.0 was used to test the proposed model ( Figure 14.1 ). The path analysis technique used measures to the extent that the model fit a data set and allowed testing of interrelationships between a range of variables simultaneously. A bootstrapping technique was conducted using the data because this procedure has been advocated as the best approach when sample sizes are small to medium (<200). 31 In addition, the bias-corrected 95% confidence interval (CI) bootstrap percentiles were used because these have been shown to be more accurate when dealing with smaller sample sizes and mediation effects. 31,32 A preselection criterion was used for the path analysis and only baseline predictors of follow-up OHRQoL (DHEQ) that had P<0.20 were entered into the model (based on Spearman and Pearson correlations). Maximum likelihood was used and adequacy of overall model fit was assessed using five fit indices including the following: chi-square test statistic, which should not be significantly different from the observed data chi-square divided by degrees of freedom (CMIN/df), which should be lower than 2.0 root mean-squared error of approximation (RMSEA), which should be less than 0.08 incremental fit index (IFI), which should be more than 0.95 and standardized root mean square residual (SRMR), which should be less than 0.08. 33–35 The error variances between illness beliefs were allowed to correlate freely. Missing data were replaced by the item’s median score to generate total scores. However, if more than 50% of the values for any given questionnaire were missing, then total scores were not calculated. Within the SEM analysis, the regression imputation technique handled this missing data.

Figure 14.1 . Direct pathways hypothesized between clinical variables, illness beliefs, pain-related coping and follow-up quality of life impacts experienced by adults with dentine hypersensitivity tested within model 1.

Note: Variables in pale grey not entered into final model because these were nonsignificant predictors of the primary outcome variable (follow-up OHRQoL).

Darwinism after Mendelism: the case of Sewall Wright's intellectual synthesis in his shifting balance theory of evolution (1931)

Historians of science have long been agreeing: what many textbooks of evolutionary biology say, about the histories of Darwinism and the New Synthesis, is just too simple to do justice to the complexities revealed to critical scholarship and historiography. There is no current consensus, however, on what grand narratives should replace those textbook histories. The present paper does not offer to contribute directly to any grand, consensual, narrational goals but it does seek to do so indirectly by showing how, in just one individual case, details of intellectual biography connect with big picture issues. To this end, I examine here how very diverse scientific and metaphysical commitments were integrated in Sewall Wright's own personal synthesis of biology and philosophy. Taking as the decisive text the short final section of Wright's long 1931 paper on 'Evolution in Mendelian populations,' I examine how his shifting balance theory (SBT) related to his optimum breeding strategy research, his physiological genetics, his general theory of homogenising and heterogenesing causation and his panpsychist view of mind and matter and I discuss how understanding these relations can clarify Wright's place in the longue durée of evolutionary thought.

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