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Definition: Dobzhansky, Theodosius from Philip's Encyclopedia

US geneticist and authority on human evolution, b. Russia. He was influential in the development of population genetics. His writings include Genetics and the Origin of Species (1937), Mankind Evolving (1962), and Genetics of the Evolutionary Process (1970).

Summary Article: Dobzhansky, Theodosius (1900-1975) from The Hutchinson Dictionary of Scientific Biography

Place: United States of America, Russian Federation

Subject: biography, biology

Russian-born US geneticist whose synthesis of Darwinian evolution and Mendelian genetics established evolutionary genetics as an independent discipline. He also wrote about human evolution and the philosophical aspects of evolution.

Dobzhansky was born on 25 January 1900 in Nemirov, Russia, the son of a mathematics teacher. His family moved to Kiev in 1910 and Dobzhansky first attended school there. In 1917 he went to Kiev University to study zoology and, after graduating in 1921, remained there to teach zoology until 1924, when he moved to Leningrad University as a teacher of genetics. Also in 1924 he married Natalia Sivertzev, whom he met while teaching at Kiev. In 1927 Dobzhansky went as a Rockefeller Fellow to Columbia University, New York City, where he worked with Thomas Hunt Morgan, one of the pioneers of modern genetics. Morgan moved to the California Institute of Technology in 1928 and, impressed with Dobzhansky's ability, offered him a post teaching genetics there when his fellowship ended in 1929. Dobzhansky, who had become a US citizen in 1937, remained at the California Institute of Technology until 1940, when he returned to Columbia University as professor of zoology. He then worked at the Rockefeller Institute (later the Rockefeller University) from 1962 until his official retirement in 1971, after which he moved to the University of California at Davis, where he remained until his death on 18 December 1975.

Dobzhansky's most important contribution to genetics was probably his Genetics and the Origin of Species (1937), which was the first significant synthesis of Darwinian evolutionary theory and Mendelian genetics - areas in which there had been much progress since about 1920. This book was highly influential and established the discipline of evolutionary genetics.

Dobzhansky's other major contribution was his demonstration in the 1930s that genetic variability within populations is greater than was then generally thought. Until this work the consensus of opinion was that, in the wild state, most members of a species had the same ‘wild-type’ genotype and that each of the wild-type genes was homozygous in most individuals. Variant genes were usually deleterious mutants that rapidly vanished from the gene pool. Furthermore, when an advantageous mutation appeared, it gradually - over several generations - increased in frequency until it became the new, normal wild type. Working with wild populations of the fruit fly Drosophila pseudoobscura, Dobzhansky found that, in fact, there is a large amount of genetic variation within a population and that some genes regularly changed in frequency with the different seasons. Continuing this line of research, he also showed that many of the variant genes are recessives and so are not commonly expressed in the phenotype - a finding that disproved the original assumption of a high level of homozygosis in wild populations. Furthermore, he found that heterozygotes are more fertile and better able to survive than are homozygotes and, therefore, tend to be maintained at a high level in the population.

Dobzhansky also investigated speciation and, using the fly D. paulistorum, proved that there is a period when speciation is only partly complete and during which several races coexist. In addition, he wrote on human evolution - in which area his Mankind Evolving (1962) had great influence among anthropologists - and on the philosophical aspects of evolution in The Biological Basis of Human Freedom (1956) and The Biology of Ultimate Concern (1967).

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