Male chimps prefer older females, study finds

Chimpanzees may be our closest biological relatives, but male chimps appear to differ from male humans in one striking way -- they clearly prefer older females, according to new research.

Martin Muller of Boston University and his colleagues analyzed detailed data collected about the behavior patterns of chimps living in the Kibale National Park in Uganda from 1996 to 2003.

In contrast to humans, the researchers found, male chimps find older females more desirable, approaching them more often to mate, fighting more with other males over them and mating with them far more frequently than with younger females. That is true even for higher-ranking male chimps, which have more choice of mates. The findings confirm the earlier results of other researchers.

"Multiple lines of evidence indicate that unlike humans, female chimpanzees become more sexually attractive with age," the researchers report in the Nov. 21 issue of the journal Current Biology. "This study demonstrates that male chimpanzees do not merely disdain young females, but actively prefer older mothers to younger mothers."

The researchers attributed the difference to a combination of factors. Humans tend to form long-term bonds, which favor a younger female mate to maximize the chances of mating again. Chimps, in contrast, are promiscuous.

In addition, female chimps are fertile throughout their lives, enabling them to have offspring even late in life.

Regardless of the explanation, the findings clearly show that chimps and humans have evolved differently in this important way, the researchers said.