"Given that there is no strong selective pressure for female spider monkeys to remain in their natal group...selection for males to disperse from the natal group due to inbreeding avoidance is relaxed (Wrangham, 1980; van Hooff and van Schaik, 1994). As a consequence, males can be the philopatric sex and develop strong relationships with one another capitalizing on the degree of familiarity and possibly kinship (Di Fiore and Campbell, 2007; Shimooka, 2005).
Further evidence suggests that adult males have the strongest bonds aside from the mother-offspring bond in spider monkey communities (Fedigan and Baxter, 1984; van Roosmalen and Klein, 1988; Symington, 1990). Ateles geoffroyi males are more likely to be encountered in the company of other males than females are in the company of other females. The males are also more affiliative than adult females, selectively directing their affiliative efforts toward other males, and grooming is the most frequent in male-male dyads (Ahumada, 1992)." Spider Monkeys; Behavior, Ecology and Evolution of the Genus Ateles. Edited by Christina J. Campbell, 2008