KIN SELECTION, SOCIAL-STRUCTURE, GENE FLOW, AND THE EVOLUTION OF CHIMPANZEES

Hypotheses about chimpanzee social behavior, phylogeography, and evolu tion were evaluated by noninvasive genotyping of free-ranging individu als from 20 African sites. Degrees of relatedness among individuals in one community were inferred from allele-sharing at eight nuclear simp le sequence repeat (SSR) loci. Males are related on the order of half- siblings, and homozygosity is significantly increased at several SSR l oci compared to Hardy-Weinberg expectations. These data support the ki n-selection hypothesis for the evolution of cooperation among males. S equence variation patterns at two mitochondrial loci indicate historic ally high long-distance gene flow and clarify the relationships among three allopatric subspecies. The unexpectedly large genetic distance b etween the western subspecies, Pan troglodytes verus, and the other tw o subspecies suggests a divergence time of about 1.58 million years. T his result, if confirmed at nuclear loci and supported by eco-behavior al data, implies that P. t. verus should be elevated to full species r ank.