Selfish sentinels in cooperative mammals

Like humans engaged in risky activities, group members of some animal socie ties take turns acting as sentinels. Explanations of the evolution of senti nel behavior have frequently relied on kin selection or reciprocal altruism , but recent models suggest that guarding may be an individual's optimal ac tivity once its stomach is full if no other animal is on guard. This paper provides support for this Last explanation by showing that, in groups of me erkats (Suricata suricatta), animals guard from safe sites, and solitary in dividuals as well as group members spend part of their time on guard. Thoug h individuals seldom take successive guarding bouts, there is no regular ro ta, and the provision of food increases contributions to guarding and reduc es the Latency between bouts by the same individual.