Speciation as a Stage in Evolutionary Divergence

Abstract

Evolution involves increase of the diversity of the organisms, as well as subdivision of the living beings into discontinuous groups (races; spp., genera, etc.) that are prevented from interbreeding by isolating mechanisms. It seems reasonable to restrict the term "speciation" to the processes of the development of isolating mechanisms. The origin of isolating mechanisms is customarily regarded as a by-product of the accumulation of genetic differences at large. This theory may not be correct; the development of isolating mechanisms may be a separate process. If each incipient species represents an adaptive complex of genetic elements, then natural selection will favor an accumulation of genetic changes that hinder or prevent the interbreeding of such spp. Gradually a physiol. isolating barrier will be built up. The development of isolation may proceed best at the boundaries where the distribution regions of the incipient spp. come into contact or overlap.