Biographical Sketch
Harvard's Ernst Mayr,
one of the architects of the modern Synthetic Theory of evolution and a
historian of biology, points to one particular book that heralded the
beginning of the new understanding and was more responsible for it than
any other: Theodosius Dobzhansky's Genetics and the Origin of
Species, published in 1937.
It was Dobzhansky's first book, but he probably would
never have found the time to write it if he hadn't been forced to spend
weeks in bed after a horseback riding accident. A Russian immigrant who
came to work at T. H. Morgan's "fly room" at Columbia University in
1927, Dobzhansky brought to America the innovative techniques developed
by Russian geneticists before their science was crushed by the tragic
madness of Lysenkoism. [See
Lysenkoism.] Versed in the research problems of both field
naturalists and lab men, he was able to make connections between the two
approaches.
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Theodosius Dobzhansky |
During the first 20 years of the 20th century, Darwin's
theory of natural selection had fallen out of favor among scientists. Many
thought it insufficient to explain the origin of adaptations, while new
discoveries of gene mutations seemed to them to be incompatible with
Darwinian models of change. But in
Genetics and the Origin
of Species, as historian Bentley Glass put it, "for the first
time, the profound signance of the work done in population genetics in
Russia and Germany was combined with an expositon of the new neo-Darwinism
stemming from R.A.
Fisher, Sewall
Wright, and J.B.S. Haldane, to produce
what has been called the modern synthetic evolution."
Dobzhansky's book was the first systematic overview
view encompassing organic diversity, variation in natural populations,
selection, isolating mechanisms (a term he coined) and species as natural
units. Later, working with Sewall Wright, he went on to demonstrate how
evolution can produce stability and equilibrium in populations rather
than constant directional change.
His studies of isolating mechanisms identified
non-genetic barriers to reproduction, such as behavior or
vocalizations, which may keep populations distinct even after
geographical barriers to interbreeding are removed. Dobzhansky also
helped demonstrate that a population arbitrarily divided into two
subpopulations can diverge into two species even in the absence of
any selection pressure. Among other projects, he studied the
mechanisms of genetic variability within natural populations and
showed how detrimental genes can spread in certain combinations with
beneficial ones (heterozygote fitness.)
He was particularly fascinated with unraveling the
multiple effects of a single genetic change (pleiotropy) and with the
complex role of gene arrangement and chromosomal structure in producing
evolutionary change. Never content with laboratory studies alone, he
repeatedly stalked wild populations of fruit flies in the mountains of
Arizona, New Mexico, California and even the rain forests of Brazil.
Dobzhansky's intimate familiarity with the processes of variation and
evolution in these fast-breeding insects also enabled him to apply his
methods to understanding variation and change in human populations.
[ Richard Milner,
The
Encyclopedia of Evolution, New York: Facts on File, 1990, p. 143. ]
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