Co-evolution of vocal communication and sociality in primates.

Understanding the rules that link communi- cation and social behaviour is an essential pre- requisite for discerning how a communication system as complex as human language might have evolved. The comparative method offers a powerful tool for investigating the nature of these rules, since it provides a means to examine relationships between changes in communi - cation abilities and changes in key aspects of social behaviour over evolutionary time. Here we present empirical evidence from phylogeneti- cally controlled analyses indicating that evol- uti onar y i ncreases i n the si ze of t he vocal repertoire among non-human primate species were associated with increases in both group size and time spent grooming (our measure of extent of social bonding).