Behavioral studies of our close relatives the chimpanzee often reveal origins of what we believe to be distinctly "human" interactions. Grooming behavior, child rearing and even gang formation have all been identified in chimpanzee populations, but in a recent study conducted in Tanzania, researchers from Arizona State University say that they may have found the origins or far more disturbing behavior-bullying and male-on-female violence.
Reporting their findings in the journal Current Biology this past Thursday, Nov. 13, the 17 year study conducted on the Kasekela chimpanzee community in the Gombe National Park, Tanzania says that they've discovered evidence that male aggression towards females is an adaptive trait leading to increased reproductive success in the population. The sexual coercion hypothesis was supported by 17 years of observation, in which males who directed aggression at desirable females mated more often than other males. And at peak times of fertility, females also sought out male aggressors to solicit them for mating.
"It is certainly not a happy message" Arizona State university evolutionary anthropologist Ian Gilby, lead researcher of the study, says. "Males who directed aggression toward females at high rates were more likely to sire those females' offspring than less violent males were."
"This effect was particularly strong for high-ranking males in the chimpanzee community."
While this study is the first study to present strong genetic evidence of long-term sexual coercion as an adaptive strategy in mammalian species, the researchers believe that the evidence may also point towards more serial aggressive behavior, much like bullying they estimate to be a marker of the aggressive males' success.
Aggression in the population took form in violent physical attacks including biting and striking that sometimes caused wounds to the females, and even included violent outbursts in which the males would charge and strike nearby flora.
As the study reveals that male-on-female aggression is a staple of the species' mating success, many have drawn anecdotal relationships to human domestic violence in headlines revolving around the debut of the research. However, lead researchers ask the general public, and fellow researchers, to consider the vast differences that exist between our species and chimpanzees, and point towards a rich evolutionary history to detract from any obvious simple relationships drawn to human behavior from the study.
"We should be careful not to jump to conclusions" Gilby warns. "Chimpanzees are one of our closest living relatives, but 7 million years of evolution separate us, and out mating systems are very different."
"Nevertheless, recognizing the adaptive value of male-female aggression in chimpanzees may ultimately helps us to understand, and hopefully prevent, similar behavior among humans."
