Fisher the evolutionary biologist

Summary. Fisher's pioneering work in linking Darwinism and Mendelism is now built into biology, but the result that he viewed as holding the ‘supreme position in biology’, the fundamental theorem of natural selection, has a more chequered history. Recent work has shown the theorem to be true, despite many earlier refutations, but its interpretation has been in doubt. I defend Fisher's own evaluation of its significance and argue that it shows that non-random gene frequency changes are always adaptive, and that adaptation arises only through gene frequency changes: this is Fisher's ‘genetical theory of natural selection’.