The Role of Small Populations for the Differentiation in Plants

Summary When trying to answer the question whether the effects of genetic drift have evolutionary significance, we must keep in mind that a local population is normally a dynamic system, changing in size, splitting into minor entities, or merging into larger complexes. Most populations have certainly been small for longer or shorter periods, and hence the role of genetic drift must not be neglected. The main role of genetic drift in the complex processes involved in the evolution of plants may be (1) the introduction of genetic factors, which are primarily non‐adaptive, (2) the rapid fixation of genetic changes, and (3) the breaking down of rigid gene blocks. Generally speaking a population may be said to be in a selective phase when it is large and in a creative phase when it is small.