Evolutionary biologist and neo-Darwinian Theodosius Dobzhansky dies in California at the age of 75. A Ukrainian-born American geneticist and zoologist, Dobzhansky has made important contributions to the development of the study of genetics and the understanding of how evolution works.
He has become especially famous for the saying, in defense of the importance of evolution in the biological sciences:
"Nothing in biology makes sense except in the light of evolution."
Dobzhansky performed a number of studies in the genetics of populations, mainly with fruit flies, which have served as a basis for explaining how races and species may have evolved through adaptation. One curious discovery of his was the fact that successful members of a species tended to carry a large number of genes which appeared to have no function at all.
Evidently, the existence of these genes contributed to overall genetic diversity within a population and reproductive success was somehow tied to the perpetuation of this diversity, eventually allowing future offspring to better adapt to unpredictable environmental changes.
Partly as a result of his work, he defined species in a way that continues to form the basis for how speciation is understood today:
"[Species is] that stage of the evolutionary divergence at which the once actually or potentially interbreeding array of forms becomes segregated into two or more separate arrays which are physiologically incapable of interbreeding."
In other words, two species are two different groups of animals which are, at their present stage of development, unable to successfully breed with each other.
Dobzhansky also argued that human culture, even though it was largely conditioned through heredity, could not be fully understood through biological factors alone. Dobzhansky feared that too great of an emphasis on the genetic variables behind human cultural development might lead to increased racism and class prejudice.