Primate play vocalizations and their functional significance.

It is well known that, among mammals, specific play vocalizations are produced exclusively by certain nonhuman primate species. In order to investigate the functional significance of these calls, we examined their phyletic distribution among New World and Old World monkeys. The results indicate that such calls are produced by species in which allomothering behaviour occurs. We propose a functional explanation of play vocalizations according to which they serve as a possible source of information for maternal retrieval of infants whenever necessary.