Sewall Wright
1984 Balzan Prize for Genetics
For his fundamental contribution to the understanding of the genetic phenomena on which evolution is based and for the formulation of mathematical models of the modification of gene frequencies in populations. For important achievements in the fields of physiological genetics and the improvement of animal breeding and plant cultivation.
Sewall Wright (*1889 - †1988), born in Melrose, Massachusetts, on December 21, 1889, is universally considered one of the foremost genetics scholars of this century. His most widely known contribution to science is the development of mathematical models of the fundamental evolutionary processes, on the basis of Mendelian genetics. The theory of stochastic changes in small populations has led him to the formulation of a principle which is generally known as the « Sewall Wright effect » or « genetic drift », i.e. the fact that chance happenings in small populations may have important effects in modifying gene frequencies, independently of natural selection. The mathematical theory of evolution developed by Sewall Wright emphasises the balance among the various forces that interact in determining the evolutionary path. It is one of the pillars upon which is founded the modern concept of evolution based on Mendelian genetics.
The mathematical study of mating systems, which was fundamental to the theoretical treatment of evolutionary problems, led Wright to consider animal and plant breeding and the inheritance of characters of economic value, such as size, weight, yield and other quantitative traits. The theoretical and experimental work he performed provided the basis to the standard knowledge and methodology of livestock breeding. Some students of Wright were able to translate his theoretical foundations into practical breeding procedures, which are currently applied in the improvement of plants and animals.
Starting from these viewpoints Sewall Wright has elaborated particular statistical methods to be used especially in the field of correlation analysis. Such methods have found application not only in livestock breeding, but in diverse areas of biology and of social sciences.
Highly significant are also Wright’s contributions to physiological genetics, which are based on his lifelong experimental work on the genetics of hair and skin color of guinea pigs. They have opened new perspectives on the subject of pigment genetics in mammals. Moreover, the analytical methods he invented, the quantitative theory be developed on the role of genes as producers of enzymes, anticipated new developments of biochemical genetics.
Sewall Wright’s first scientific paper dated 1912 has been followed by more than 200 papers, up to 1982. The list is crowned by a four volume treatise on Evolution and the Genetics of populations published from 1968 to 1978, which is a synthesis of the science of genetics considered mainly from the evolutionary point of view, but taking also into account its structural, physiological, biochemical aspects.
A long life entirely devoted to the development of genetics and evolutionary theory, as well as to important practical applications, and which has led to fundamental scientific achievements in several fields, well deserves the award of the 1984 Balzan Prize for Genetics.

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