Aggressive male chimpanzees who consistently bully females tend to father more babies with their victims, a new study has said.
The findings, published in the US journal Current Biology, were based on a long-term study of interactions between chimpanzees in the famous Gombe National Park in Tanzania.
"These results seem to suggest that males are selected to be aggressive toward females to increase their paternity success, which explains why male-female aggression is observed in so many chimpanzee populations," first author Joseph Feldblum of Duke University said in a statement Thursday.
Chimpanzee males are known to direct surprising amounts of aggression toward their female group mates, according to the researchers, but previous studies of mating success had found evidence both for and against the presence of sexual coercion in wild chimps, Xinhua reported.
To help settle the debate, Feldblum and his colleagues looked to a chimpanzee community living in the Gombe National Park that had been under close observation for the last 50 years.
The researchers knew not just who had mated with whom, but also who the biological fathers of nearly all chimpanzees born in the community since 1995 were, based on genetic tests of paternity.
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The researchers examined the effect of male aggression toward females both when the females were sexually receptive and when they were not.
Their analyses showed that male aggression during a female's sexually receptive periods led to more frequent mating but not greater paternity success.
On the other hand, high-ranking males that showed aggression toward females when those females were not sexually receptive were rewarded for their bullying with more offspring.
The findings showed that long-term patterns of intimidation allow high-ranking males to increase their reproductive success, offering what may be the first genetic evidence of sexual coercion as an adaptive strategy in any social mammal, the researchers said.
The findings in chimps, however, probably did not have much to tell mankind about sex and parenthood in human society, despite the close evolutionary ties between human beings and chimps, they noted.
"The glaring difference between chimpanzee and human mating behaviour is that in chimpanzees females mate promiscuously with most male group mates during most cycles, while human females do not," Feldblum said. "Thus, the system that favours male coercion in chimpanzees is not present in humans to favour this behavior. "
Feldblum said he was now interested to find out whether some males might find success in paternity in kinder, gentler ways, for instance, by spending more time grooming females.