杏吧原创

Chimpanzees trade precious scraps of meat for sex, new research shows. A two-year study of wild chimps finds that males boost their chances of having sex with a female by offering her meat.

But don鈥檛 call them prostitutes. 鈥淚t鈥檚 not like 鈥業 give you meat and a few hours later you鈥檙e going to copulate with me,'鈥� says Cristina Gomes, a primatologist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.

She and colleague instead uncovered more nuanced and long-term exchanges.

This could be why others who have studied meat-for-sex trades between chimpanzees turned up equivocal or negative results, Gomes says. Previous studies found that males are just as likely to share meat with sexually active, oestrous females as with non-oestrous females, who don鈥檛 have sex. Males, also, seem no more eager to hunt or share meat when females are likely to get pregnant.

However, Gomes previously found that chimpanzees in Ivory Coast鈥檚 Ta茂 National Park exchange back scratches over a long period of time, and wondered whether meat-for-sex trades aren鈥檛 so immediate either.

Whimpering pleas

To make this case, her team recorded meat-sharing over 22 months, noting who gave meat to whom. After a successful monkey hunt females tended to surround a male hunter and make whimpering pleas. In some cases, the male handed meat to a female, but more often than not he simply allowed her access to the carcass. The male with the meat decides who gets it, Gomes says.

Separately, she spent a total of 3000 hours following individual chimps from dawn to dusk, noting who mated with whom. After crunching all this data, she and Boesch found clear evidence pointing to meat-for-sex exchanges. On average, males who shared meat with a specific female were twice as likely to mate with her, compared to a less generous male, they found.

Whether a female was in oestrous or not when they received meat didn鈥檛 seem to make much of a difference. When Gomes鈥� team analysed only meat-sharing with females who couldn鈥檛 get pregnant, the meat-for-sex relationship remained clear. 鈥淭hat means that it鈥檚 not a short-term thing,鈥� she says.

Her team鈥檚 analysis did not determine how long it took for these exchanges to even out. Nor could they tell if males who share extra meat get even more sex than males who share less.

Gomes also isn鈥檛 sure if all chimpanzees exchange meat for sex. In Gombe National Park in Tanzania, for instance, males tend to be more coercive than at Ta茂 National Park. 鈥淚f males are just forcing females to copulate with them, they don鈥檛 need to share meat,鈥� Gomes says.

Female chimpanzees at Gombe still get meat, says , a

Harvard University anthropologist who studies hunting and meat-sharing in the park. However Gombe females are more direct in their demands, often snatching at the carcass and putting their hands in front of a male鈥檚 mouth to prevent him from eating. Such persistence could explain meat-sharing instead of sex trades, he says.

Still, Gilby says the new work will 鈥渓iven the debate over whether chimpanzees trade meat-for-sex.鈥�

Human parallels

Even if meat-for-sex trades aren鈥檛 the rule in all chimpanzee communities, the exchanges may help understand why, in some human cultures, the best male hunters father the most children, Gomes says.

Anthropologists have suggested that women prefer higher-status men and that children of the best hunters get better treatment and are more likely to survive, but Gomes wonders if meat-for-sex trades might also play a role.

鈥淲e have to go back and study humans more carefully and try to see if we can determine if they exchange meat for sex,鈥� she says.

Journal reference: PLoS One (DOI: 10.1371/journal.pone.0005116)