Bonobos and chimpanzees may look alike, but behaviorally they are very different. Chimps are aggressive and warlike, and males dominate. Bonobos are more peaceful and tolerant and females rule. These two primate species are our closest living relatives (we share nearly 99 percent of our DNA), and humans share traits with both species. Some people are more like bonobos, and others more like chimpanzees.
A new study published this week in PNAS shows that most human males are hormonally similar to bonobos when in a competitive scenario, but those men striving for a high status are more like chimps.
The biologists conducting the study began by documenting changes in the levels of two hormones—cortisol and testosterone—in 12 pairs of bonobos and 24 pairs of chimpanzees presented with a situation in which they had to compete for food. The scientists used cotton swabs dipped in Sweet Tart dust (Sweet Tarts stimulate saliva production in primates) to collect saliva before and after the pairs were presented with a pile of food.
Previous research has shown that when human males are faced with a competition of some sort, your average guy will experience increases in levels of glucorticoids like cortisol. Men who are striving for a high status, however, exhibit increases in testosterone levels. And when the competition is over, winners (of either type) have an increase in testosterone and losers a decrease.
Bonobos are like the average guy, according to this new study. Prior to competition, they experience an increase in cortisol, which is associated with stress and a passive coping strategy. Chimps are like the men striving for power; their testosterone levels increase prior to competition and they react as if the situation is a threat to their status.
But humans are the only primate species out of the three to experience changes in hormone levels after the competition is over. ‘It’s exciting because we can see that in some ways we’re similar to bonobos, in others we’re similar to chimpanzees,” says Brian Hare of Duke University. “But then there’s also a part of our biology that seems to be entirely unique.”