Male chimpanzees, Pan troglodytes, differ from males in most other mammalian taxa because they remain in their natal communities throughout their lives, form close bonds with one another, and cooperate in a range of activities . However, males also compete fiercely for status within their groups [2,3], and high rank enhances male reproductive success [4,5]. Males rely partly on coalitions to achieve and maintain status [2,3,6-9], and shifts in male alliances can have dramatic political effects [2,3,6]. It is not known what benefits are obtained by low-ranking coalition partners. Here we report that the highest-ranking (alpha) male in one well-studied community of chimpanzees rewarded his allies by allowing them preferential access to mates.