ABSTRACT
In 1937, Theodosius Dobzhansky published a book called Genetics and the Origin of Species, which is widely regarded as ushering in an intellectual era in biology, hailed as the triumph of neoDarwinism, and called the modern evolutionary synthesis. Dobzhansky integrated his experience as an experimental geneticist in the laboratory with the observations of naturalists working on populations in the field to show that populations of similar individuals contained sufficient genetic diversity for natural selection (differential reproduction) to theoretically bring about evolution in a gradual fashion and this without the assistance of the dubious mechanism of the inheritance of acquired characteristics. In other words, Dobzhansky, using Weismann’s and Mendel’s concept of “hard inheritance”—genes are unalterable by the organism’s life experience and genes give rise to charactersforged a populationgenetic view of evolution that overcame Darwin’s problem of blending inheritance and the need to appeal
to Lamarck’s use-inheritance. The best adapted organisms in a population had the most surviving offspring and thus contributed more of their genetic material to the next generation ad infinitum until, eventually, a new species would arise as a result of this longcontinued process of selection of the best adapted individuals and the favoring (even slightly) of their unique genotypes into the indefinite future. A very important theoretical component of the modern synthesis is the idea that some organismic variation is
heritable and some is not heritable and it is only the heritable variation that is significant for evolution. This view stems inevitably from population-genetic thinking, which holds that there are two sources of variation, one genetic and the other environmental. According to this viewpoint, it is only the former, of course, that can be inherited. (As we shall see later in this chapter, this overly simple idea requires substantial modification, but for the period we are describing it worked very well.)
In the third edition of his book, in 1951, Dobzhansky identified evolution as occurring at the level of populations and, more specifically, in the genetics of populations: “Evolution is a change in the genetic composition of populations. The study of mechanisms of evolution falls within the province of population genetics” (p. 16). The rules that govern the genetic structure of populations are different from the rules that govern the genetics of individuals.
