Chapter 3. The Effects of Complex Social Life on Evolution and Biodiversity

Summary

Social vertebrates display faster chromosomal evolution, faster species turnover, and higher levels of allelic heterozygosity than nonsocial vertebrates. At least some species also display substantially more genetic differentiation among geographically spaced social groups. The explanation for this pattern may be that matrilines stay together over multiple generations to compose such groups, and a relatively small number of males inseminate them. In contrast, higher social insects, comprising the termites, ants, eusocial bees, and eusocial wasps, have slower rates of evolution, similar to that of other, related groups of insects. The explanation appears to be that their population structure is very different from that of vertebrates: from the view-point of genetics their colonies are actually individuals (superorganisms), and the population equivalent to the local vertebrate society (= population) is the population of colonies. Moreover, outbreeding is extensive. The four major assemblages of highly social organisms – the colonial invertebrates, eusocial insects, nonhuman social mammals, and man – are characterized for the most part by great biomass, interspecific competitive superiority, and low species diversity. Competitive superiority in colonial invertebrates and eusocial insects over nonsocial animals is achieved substantially by social means. Lower species diversity on the other hand is due substantially to large organism size, where invertebrate clones and insect colonies are the equivalent of the organisms composing nonsocial species.