Although some M. mulatta show mate preferences, in general they are highly promiscuous. Males improve their chances of passing their genes on to the next generation by attempting to mate with as many females as possible. They enjoy being in water and are good swimmers. Usually, they live in groups of up to two hundred individuals. When a group's size reaches 80-100 members, a subgroup of females may split off to form a new group.
Populations generally consist of a few unrelated males and many closely related females.
Sometimes small groups form that consist of only males. Males usually leave the group in which they were born shortly after they reach sexual maturity. Offspring born to a mother and son, or to siblings, are very rare. Both males and females in a group show a preference for high ranking members of the opposite sex. Dominance hierarchies exist in both sexes of M. mulatta .