Chimps’ mating calls contain careful calculation

I’ve stumbled upon this article by Nicholas Wade in the International Herald Tribune.

Intricate as the mating dance may be among people, for other primates like chimpanzees and baboons it is even more complicated. This is evident from the work of researchers who report that the distinctive calls made by female chimpanzees during sex are part of a sophisticated social calculation.

Biologists have long been puzzled by these copulation calls, which can betray the caller’s whereabouts to predators. To compensate for this hazard, the calls must confer a significant evolutionary advantage, but what?

The leading explanation involves the way female primates protect their offspring. Male chimps and baboons are prone to kill any infant they believe could not be theirs, so females try to blur paternity by mating with as many individuals as possible before each conception. A side benefit is that by arranging to have sperm from many potential fathers compete for her egg, the female creates conditions for the healthiest male to father her child.

The calls that female chimps make during sex seemed to be just part of this strategy. By advertising a liaison in progress, biologists assumed, females stood to recruit many more partners.


Unlike female baboons, who give a staccato whoop at each copulation, the chimps seem much more aware of the social context.

Chimps are particularly likely to be silent and conceal their liaisons when higher-ranking females are nearby. They were most acoustically exuberant when cavorting with a high-ranking male.

The reason may be that other higher-ranking males are also likely to be around, and by advertising her availability to them a female chimp may gain many influential protectors for her future infant.

The calculus changes when higher-ranking females are around because they are likely to attack the caller and break up the fun. To avoid incest, young females leave their home group and try to integrate with neighbors by offering themselves to socially important males. But the resident females tend to be obstructive, perhaps because they see the visiting females as competitors for male protectors and desirable feeding areas.

A similar use of copulation calls could once have existed in the human lineage but if so, it may have lost its evolutionary advantages when human societies developed their distinctive system of pair bonding and made intercourse a largely private activity.


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