EVOLUTION OF MAMMALIAN SOCIAL-STRUCTURE

Social groups may be viewed as collections of individuals exhibiting n onindependent behavior and organized in a cooperative manner. The evol utionary advantage of social behavior to individuals must be measured in its relativity to other potential behaviors, the scale of competiti ve interactions, and under a variety of environmental and genetic cons traints. A primary tenet of social evolution is that coancestry will p romote the genes of related individuals. High values of coancestry, ho wever, do not necessarily translate into evolutionary advantage unless the primary competitive interactions occur among the groups. Coancest ry is affected by the breeding tactics within and rates of genetic exc hange among social groups. Low rates of exchange among groups, regardl ess of breeding tactics, may result in high values for intragroup coan cestry but may lead to inbreeding depression in progeny. Likewise, bre eding tactics such as polygyny, may not impart any long-lasting evolut ionary advantage if genetic exchange rates are high. The evolution of social organizations typified by different breeding and migration stra tegies is evaluated to determine the conditions necessary for various tactics to result in genetic contributions by individuals equal to tho se of monogamous mating systems. The models show that breeding and dis persal tactics have probably evolved in concert and predict that socia l-groups which are characterized by strong gene correlations are likel y to exhibit relatively low group advantage for progeny survival and b reeding. There is little impetus for high gene correlations to accrue in situations where group advantage is very high relative to monogamou s systems.