First report of food sharing among nicobar long-tailed macaques

Abstract

The sharing of food is an essential component of human societies and has likely played a key role for the evolution of several human traits such as reduced sexual dimorphism, a more flexible maturational pace in relation to environmental variation and an increase in human tolerance and co-operation. For this reason, the investigation of the evolutionary origins of food sharing in humans has been a central topic in biological anthropology. Since behavior does not fossilize, investigations on food sharing in non-human primates are key in providing a window into the evolution of food sharing and co-operation in humans. Among non-human primates, evidence of non-kin food sharing has largely been found in apes and New World monkeys, while this phenomenon has rarely been reported in Old World monkeys. Here we provide the first descriptive report of food sharing in wild macaques. We studied two free-ranging groups of Nicobar long-tailed macaques from two different islands (i.e., Great Nicobar and Katchal), that have very different ecological settings and vegetation, for over 168 days. Using focal animal sampling, we observed a total of 18 food sharing events, that revolved around monopolizable food items (coconut and termite log) and mostly involved males. Females, even when present near the food owner, took very little interest in observing the event. The macaques shared food only among the individuals who sat close to the food owner, who, in turn, displayed very little aggression against bystanders. Given that, among Nicobar macaques, males have been previously described as forming strong social relationships, and since harassment was rarely observed in the present study, we argue that our observations could support the reciprocal exchange rather than the harassment hypothesis. While more observations are needed to better clarify the ultimate function of food sharing in this species, our study on Nicobar long-tailed macaques highlights some features that might make this species an ideal model to study the evolution of human behavior.