Male chimpanzees prefer mating with old females

The findings uncover a stark contrast between chimpanzee behavior and that of humans, their primate cousins. The basis for this difference may lie in the fact that whereas chimpanzees participate in a relatively promiscuous mating system, humans form unusually long-term mating bonds, thereby making young females more valuable as mates with greater reproductive potential. The findings, reported by Martin Muller of Boston University and colleagues at Harvard University, appear in the November 21st issue of Current Biology.

Theoretical explanations for the preference of human males for young females as mates include the facts that humans tend to form long-term mating partnerships, and that female fertility is limited by menopause and, therefore, age. The converse of such an explanation suggests that species that appear to lack long-term pair bonding and menopause (such as chimpanzees) should not exhibit such strong preferences by males for young females.

In the new work, researchers examined this idea by studying male mate preferences within the Kanyawara chimpanzee community in Kibale National Park in Uganda. The researchers found that, in contrast to humans, male chimpanzees prefer older females to younger ones. They found that, compared to younger females, older females were more likely to be approached for copulation, were more often in association with males during estrous periods, copulated more frequently with high-ranking males, and gave rise to higher rates of male-on-male aggression in mating contests.

The findings, in addition to supporting the idea that long-term pair bonding and menopause may contribute to the preference of human males for young females, also suggest that this characteristic may be an evolutionarily derived trait that arose in the human lineage sometime after the lineages giving rise to humans and chimpanzees diverged.