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Sewall Wright was born December 21, 1889, in Melrose, Massachusetts, and died in Madison, Wisconsin, March 3, 1988. Before his third birthday, the family moved to Galesburg, Illinois, where his father, Phillip G. Wright, had accepted a teaching position at Lombard College. Wright graduated from Lombard College in 1911 and, after a year at the University of Illinois, went to Harvard University as a student of William E. Castle. After receiving the doctorate in 1915, he was employed as senior animal husbandryman by the US Department of Agriculture (USDA) in Beltsville, Maryland. He remained there until 1925, when he accepted a position as Professor at the University of Chicago. Upon retirement in 1954 he moved to the University of Wisconsin, where he stayed for the rest of his long life. Wright remained intellectually and physically active until his death at age 98, caused by his slipping on an icy sidewalk during one of his regular long walks.
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1. Early Life
Wright was a precocious child. He could read and kept a diary before starting school. He also learned arithmetic and astonished his first-grade teacher by extracting cube roots. Later he and his brothers printed the first poems of Carl Sandburg, who was a student in their father’s composition class. At Lombard he took several courses from his father, including calculus. But, despite his later reputation as a formidable mathematician, Wright never took advanced courses; his mathematics was largely self-taught. His interest in genetics was kindled by reading Punnett’s article on Mendelism in the Encyclopedia Britannica.
Between his junior and senior years of college, he used his mathematical and surveying skills to work on a railroad construction in the Standing Rock Reservation in South Dakota. It was an exciting time for him. In his 90s he enjoyed telling about the rough frontier life with cowboys, Indians, and outlaws, and he still recalled a large number of words in the Sioux dialect. This work was cut short by a lung infection. While confined to a caboose, he used the time to study Tait’s book on quaternions. As a result of the damaged lung, he later had trouble getting life insurance, something that he found increasingly amusing as he continued to live far beyond the usual life-expectancy.
Wright’s father, Philip, was a man of many talents. He taught courses in astronomy, mathematics, economics, surveying, English composition, and physical education. He loved poetry and music, and was disappointed that his son did not take to them. Later he moved to the Brookings Institute where he published a number of books on economics. Wright had two brothers who also attained distinction. Quincy became a leader in international law and Theodore was an aeronautical engineer and acting president of Cornell University.
A full length biography of Wright is available (Provine 1986), with full details of his life and scientific accomplishments. His scientific papers span the period from 1912 to 1988, an astonishing 76 years. His Bibliography: comprises more than 200 articles, including a four volume set published during his retirement (Wright 1968–78).
2. Animal Breeding
Wright’s thesis at Harvard analyzed interaction of coat colors in guinea pigs, a subject which he pursued throughout his USDA and Chicago years. He enjoyed guinea pigs and spent many hours taking care of them. Only the non-availability of an animal house prevented his continuing this after his move to Wisconsin. While at Harvard, he also began his theoretical studies of population genetics. On moving to the USDA, he inherited a colony of guinea pigs that had been inbred for many generations. His analysis of the effects of inbreeding and crossbreeding set a standard for careful analysis; the paper could be written today with hardly a word changed. During this time he invented the inbreeding coefficient, with a simple algorithm now standard textbook material (Wright 1922a). Also during this period, he formulated the basic principles for analysis of quantitative traits.
Wright, along with R. A. Fisher (see Fisher, Ronald A (1890–1962)), converted animal breeding into a quantitative science. Wright was especially proficient in manipulating correlation and regression coefficients. One of his earliest papers (Wright 1917) foreshadowed the analysis of covariance. His major statistical contribution was developing the method of path analysis. This is a way of measuring the relative contribution of different causal paths to a quantity of interest, such as size or performance. This was presented in a diagram in which causal paths were designated by arrows and correlations by curved, two-headed arrows (Wright 1921). A path coefficient, measuring the influence of a path, is a standardized partial regression coefficient. Wright formulated a set of simple rules that made the analysis easy to apply. This method enjoyed great popularity among livestock breeders, although recently it has been largely replaced by more sophisticated, computer-driven techniques that permit analysis of large bodies of data, and measurement of the precision of the estimates.
The technique is most useful for nonexperimental situations and in recent years has found its greatest use in the social sciences. Wright himself used the method in the late teens to analyse 510 correlations of 42 variables involving corn yields and prices and hog production. He could not get this monumental paper published because an animal husbandryman was not supposed to know about economics. It was not published until several years later, and only after the intervention of Henry A. Wallace, son of the then Secretary of Agriculture.
3. Evolution
After moving to Chicago, Wright changed his emphasis from animal breeding to evolution, although he still retained his interest in the physiological genetics of guinea pigs. Three people, R. A. Fisher (1929) and J. B. S. Haldane (1932) in Britain, and Sewall Wright (1931) in the USA are mainly responsible for the ‘new synthesis,’ the welding of Mendelian inheritance and Darwinian natural selection into a coherent mathematical theory. Wright’s particular contribution was the ‘shifting balance theory.’ He thought that a major difficulty in evolution was the frequent inability of a well-adapted organism to evolve into a better adapted one without passing through maladaptive intermediates. In Wright’s metaphor, a population at an adaptive peak could not move to a higher peak without passing through less well adapted intermediate stages.
Wright thought that a way out of this dilemma was to have a population broken up into partially isolated subgroups. Within a small subgroup random genefrequency changes can occur and occasionally these may produce a combination of genes that is close to that of the genotypes at the higher peak. Then, selection could take over and carry the population to the peak. This highly adapted subpopulation would then expand and send migrants to upgrade the whole population, and the process could start over.
Wright’s theory became very popular among biologists. Its emphasis on gene interactions and its offering a way of putting together adaptive combinations of genes that might be deleterious in other combinations had a wide appeal. On the other hand, the theory was less popular with mathematical theorists. Wright’s model required a delicate balance of population size, selection, and migration, which would be rare. It also required that the population spend much of its time, during the trial and error period, in a less than optimally adapted state. Finally, there is a question as to whether the theory is really needed; perhaps mass selection usually suffices for adaptive evolution.
Wright’s theory was steadily refined during the rest of his life, but the essence remained unchanged. The theory became almost an obsession with him and he delivered many talks on the subject and wrote paper after paper. It is fair to say that, as to the importance of his theory, the jury is still out. Wright’s latest paper (1988) was spirited defense of his idea, while still noting the importance of the contributions of Fisher and Haldane, and of Kimura (see Kimura, Motoo (1924–94)) who argued for the importance of mutation-driven, neutral evolution of molecular differences. He concluded that ‘all are valid.’
4. Retirement Years
After moving to Wisconsin, Wright spent the first few years finishing the analysis of his extensive guinea pig studies. These were masterful analyses, but by that time the molecular revolution had changed the nature of developmental genetics, and Wright’s methods were out of vogue. When this was completed, in his 70s he began his monumental four volume set, the last volume of which was published when he was 88 (Wright 1968–78). Although his shifting balance theory is conspicuous throughout, the book is far more than this. It summarizes, in four densely packed volumes, not only his life’s work, but the whole field of population genetics. For the last decade of his life Wright’s eyesight became progressively worse, and he used a reader that projected a greatly enlarged picture onto a television screen. He continued to read and to enjoy conversations, but in his last years he found it increasingly difficult to keep up with molecular advances and turned more to reading history and biography.
As a person, Wright was quiet, shy, and introverted. He had no small talk, and was hard to converse with. Yet, once the conversation turned to a subject on which he had an interest—and there were many—he could go on at great length. His lectures were always full of details and regularly ran overtime. He had a charming sense of humor and was excessively generous with his time. His students and colleagues held him in great affection.
5. Social Sciences And Philosophy
Wright’s greatest influence in the social sciences is his method of path analysis. It was taken up by several social scientists, such as Dudley Duncan in sociology and Arthur Goldberger in economics, and has become a standard part of the statistical methodology. One of Wright’s earliest applications of path analysis used adopted children to separate genetic from environmental influences on IQ scores, and there have been many follow-up studies extending his methods to more complex analyses of behavioral traits with better data. Finally, with the increasing interest in behavioral evolution, especially among psychologists, mathematical theories of evolution are becoming increasingly common and Wright takes a place in this, along with Fisher and Haldane.
Wright was unusual among biologists in taking an active interest in philosophy. He had a somewhat Leibnitzian view. He disliked any idea of emergence. He found no sharp borders between different levels of complexity, such as between embryo and adult or between mind and no mind. Thus if the mind does not emerge by magic, it must trace its development into a continuous process back to the embryo, the egg and sperm, and ultimately the DNA molecules. He called his concept ‘dual-aspect panpsychism.’ Mind is everywhere; so is matter.
The biological community either disagreed with Wright’s view, or was indifferent. Most regarded mind as a natural outgrowth of appropriately organized matter. Wright held on to his dualistic view, however, and found a few kindred spirits among philosophers, particular his long time colleague at the University of Chicago, Charles Hartshorne.
Bibliography:
- Fisher R A 1929 The Genetical Theory of Natural Oxford University Press, Oxford, UK
- Haldane J B S 1932 The Causes of Evolution. Longmans Green, London
- Provine W B 1986 Sewall Wright and Evolutionary University of Chicago Press, Chicago
- Wright S 1917 The average correlation within subgroups of a population. Journal of the Washington Academy of Sciences 7: 532–5
- Wright S 1921 Correlation and causation. Journal of Agricultural Research 20: 557–85
- Wright S 1922a Coefficients of inbreeding and American Naturalist 56: 530–38
- Wright S 1922b The effects of inbreeding and crossbreeding in guinea pigs Bulletin 1090: 1–63, 1091: 1–60
- Wright S 1931 Evolution in Mendelian Genetics 16: 97–139
- Wright S 1968–78 Evolution and the Genetics of 4 Vols. University of Chicago Press, Chicago
- Wright S 1988 Surfaces of selective value revisited. American Naturalist 131: 115–23