Diversification and germ-line determination

Abstract

The species richness of extant metazoan phyla displays a strong association with the ontogenetic timing of germ-line determination. Taxa with early ontogenetic determination of the germ-line are characterized by low species number relative to taxa with late or variable determination. A test for a similar association in fossil taxa is compromised by the fact that all phyla displaying early determination of the germ-line are small, soft-bodied groups which lack a reliable fossil record. To the extent that this correlation reflects causality, patterns of evolutionary diversification have been decidedly non-random. The fact that ontogenetic timing of germ-line determination defines the extent to which genetic variation arising during the course of ontogeny may be inherited suggests a possible causal foundation for the pattern.