ABSTRACT
Later on, Fisher (1930/1958), was able to show statistically, first, that if natural selection favored a relatively rare gene for a long enough period, that gene would eventually become very widespread in the population. This was the perfect complement to Darwin’s notion of the gradualness of evolution by natural selection. The importance of single-gene substitutions in polygenically determined traits is that they would eventually change the polygenic trait and thus could, in theory at least, be responsible for gradual evolutionary change. Single-gene thinking was “in the air” around the 1920s for other reasons, particularly because the experimental work of Thomas Hunt Morgan’s group of geneticists and embryologists was guided by the assumption that evolution proceeded by the replacement of one gene by another (“point mutation”) in a population of interbreeding organisms. Several other mathematically sophisticated scientists were working to show by statistical means how dominance could (theoretically) evolve depending on the selection regimen.
