Interspecific isozymic substitution is not random

Abstract

The validity of the neutral theory of molecular evolution, which holds that almost all allelic substitution during evolution has been due to random genetic drift, is a pivotal question in evolutionary biology. Here it is shown that the theory predicts a 1:1 ratio among isozymes in a species between those which are faster (i.e. have greater anodal mobilities) and those which are slower (i.e. have lesser anodal mobilities) than their homologues in a related species. In fact, observed patterns of isozymic variation display deviations from such a ratio. Significant departures from expected values were found for reptiles, fish and insects. A near significant result was seen for amphibia. The overall deviations are highly significant. The results strongly suggest that a substantial fraction of allozymic substitution has been due to positive Darwinian selection. © 1992 The Genetical Society of Great Britain.