It may come as no surprise that men can at times behave like apes. In fact, they're driven by the same primitive urges.
When faced with an impending competition, men pump out hormones that match those of either peace-loving bonobos or aggressive chimps, researchers at Duke University report. Which hormones win has to do with the guy's personality.
Though most men's bodies prep for a scrimmage by producing cortisol, the stress hormone that runs through the blood of bonobos, status-driven fellows also generate the aggression hormone testosterone, making them more like chimps.
In the aftermath of the battle, however, humans' responses are in a category all their own. Men celebrate victory with an increase in testosterone and mourn defeat with a decrease in it. Neitherbonobos nor chimps show these after-effects.
The conclusions were drawn from a new study outlining differences in chimp and bonobo hormonal responses to conflict.
The research, conducted by scientists at Duke and Harvard universities, was published Monday in the Proceedings of the National Academy of Sciences.
"It looks like before competition, human [males] are not very unusual," co-author Brian Hare of Duke said. "But after competition, they look unique."
Bonobos and chimps have long been used as models to glean insight into human behavior, as both species are our close relatives.
But the two primates deal with radically different social pressures.
For bonobos, the social environment is one of cooperation, where food sharing is common and aggression rare. Chimps, in contrast - and males in particular - often pick fights to assert dominance and establish rank.
As a result, the researchers were interested in seeing whether the apes' hormonal patterns matched their psychological dispositions.
Food fight
In a series of trials, researchers presented chimps and bonobos with an identical food competition. A pile of food was placed in a room, and saliva samples were taken both before and after the apes saw the meal in order to measure hormone levels.
Results showed that bonobos ramped up their production of cortisol when anticipating a potential fight, while chimps showed increased testosterone levels. Cortisol is typically produced in response to a stressful situation, while testosterone primes an animal for a struggle.
"The chimps respond in a way that says 'I'm gonna beat the crap out of you and I'm gonna win,' " Hare said. "The bonobos say, 'This is a stressful event; I want to get along, and I don't like not getting along.' "
Among the female primates, no consistent patterns were found. Authors say it's because competition is traditionally a bigger pressure in male circles throughout the primate world.
The findings confirm the idea that, despite their close heritage, chimps and bonobos really are different.
"These are two species as closely related as wolves and dogs, facing an identical social situation, and reacting completely differently," Hare said.
The results also help shed light on human behavior, Hare said. Previous studies have found that men tend to produce cortisol before a fight, and those who strive for power also make testosterone.
In light of the ape results, the findings suggest many males have the desire to cooperate like bonobos, though some remain driven by a chimplike desire to beat out competitors.
Not so fast
Still, not everyone agrees that the leap from ape traits to human behavior can be made so smoothly.
"Apart from noting that men who seek power react physiologically to competition more like chimpanzees than bonobos, the paper has no clear implications for understanding human social behavior," said Michael Schwalbe, a sociology professor at N.C. State University. "Trying to draw such implications is overreaching."
