8 April 2009

Chimps swap meat for sex

Cosmos Online
Sex sells, even in the rainforest. Chimps have been found to exchange morsels of food for sex, says a study that sheds new light on mate selection in the species.
Chimp with meat

Snack attack: Kinshasa, an adult female chimpanzee, holding a piece of (colobus monkey) meat she received some minutes before from Utan, an adult male chimpanzee Credit: Cristina M. Gomes

SYDNEY: Sex sells, even in the rainforest. Chimps have been found to exchange morsels of food for sex, says a study that sheds new light on mate selection in the species.

“We found that female wild chimpanzees copulate more frequently with those males who share meat with them on at least one occasion, compared with males who never share meat with them,” said lead researcher Cristina Gomes.

Her team from the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, spent three years observing chimp behaviour in the Taï National Park, Côte d’Ivoire (formerly Ivory Coast).

Sex trade

Chimpanzees are known to hunt regularly, said Gomes, and earlier field studies showed males shared meat with females, but until now the scientists were at a loss to explain exactly what they got in return for this.

Now, by studying females in active and inactive phases of their mating cycles, the reseachers have shown that males develop long-term partnerships with various females. In these partnerships, the males continuously provide morsels of meat to to the females, who in turn mate with them during sexually active phases of their cycles.

The new observations “indicate that wild chimpanzees exchange meat for sex, so that sharing meat with females improves a male’s mating success and a female’s meat intake,” said Gomes.

The results appear today in the journal PLoS ONE.

As our closest living relative, one that shares many social behaviours with humans, chimps can offer new clues to how we think about mate choice in our own species, she said.

Human behaviour

Studies of the few human societies that still lead a hunter-gatherer lifestyle today – such as the Hadza people of Tanzania – have shown that the top hunters have better reproductive success.

“In some groups good hunters have more children than non-hunters or bad hunters, whereas in others they have more wives or more extra marital affairs,” noted Gomes. “It is well known that women seek to find a partner that can provide for her and her offspring, however, to my knowledge, there has not been any evidence showing a direct link.”

She added that further studies of these hunter-gatherer societies would help determine if humans exchanged food for mating access in a similar way to chimpanzees.

Ian Gilby is an anthropologist at Harvard University in Boston, U.S., who studies chimpanzee behaviour. He praised the research but was cautious about the interpretation of its results.

“This is one of the most rigorous tests of the hypothesis that chimpanzees trade meat for sex, and adds to the growing body of data that demonstrates the considerable behavioural diversity among chimpanzee subspecies,” he said.

However, Gilby added that researchers disagree over the extent to which female chimpanzees are able to realise their mating preferences, and whether mate choice is a response to male aggression.

“If this is the case, it would seem puzzling that male chimpanzees would need to use meat in order to entice females to mate with them,” he said.

More information:
The study in PLoS One

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