Genetic Drift and the Founder Principle

Abstract

It has been explained in the last chapter that organisms automatically generate their own cycles of abundance and rarity and that the changes in selection-pressure with which these are associated may greatly increase the speed of evolution. There are, however, additional ways in which the reduction of a population to a very low level, whether permanently or recurrently, may bring about certain types of evolutionary change. That is to say, through the operation of Random Genetic Drift, or the Founder Principle, and by other means related to one or both of these concepts. This, therefore, is a convenient place in which to outline them. Once that is done, it will be possible to assess their importance (which, in respect of Drift I believe to have been greatly exaggerated) as the relevant evidence, derived as it is from numerous distinct sources, becomes available here and there in subsequent chapters of this book.