If it pays to be a jerk, why isn't everyone that way?

Throw a tantrum. Threaten, shove aside or steal from your colleagues. In other words, be a bully. Science confirms, yet again, that brutish behavior can be an effective path to power. And not just in humans, but in chimpanzees, too.

A new study appearing in the journal PeerJ Life and Environment found that male chimps with more bullying, greedy and irritable personalities reached higher rungs of the social ladder and were more successful at siring offspring than their more deferential and conscientious counterparts.

But if that’s the case, researchers ask, why isn’t every chimp a bully?

A team of UK and US researchers followed 28 male chimps living in Gombe National Park in Tanzania to try and find the answer.

A previous study of Gombe chimpanzees showed how some chimpanzees are more sociable, while others are loners. Some lean towards easy-going, while others are more overbearing or quick to pick fights.

Tanzanian field researchers who knew the chimpanzees well performed the personality assessments, based on years of near-daily observations of how each chimpanzee behaved and interacted with other chimps.

In the current study, researchers found that male chimps with certain personality traits—in this case, a combination of high dominance and low conscientiousness—tend to fare better in life than others.

What the researchers say: “Personality matters,” said the lead author of the study.

It may not be shocking to learn that bullying has its perks. But for some researchers, findings like these pose a conundrum: If males with certain personality tendencies are more likely to rise to the top and reproduce, and pass the genes for those traits on to their offspring, then shouldn’t every male be that way? In other words, why do personality differences exist at all?

“It’s an evolutionary puzzle,” the lead author told us.

One long-held theory is that different personality traits pay off at different points in animals’ lives. Even if being aggressive gives young male chimps an edge, it might backfire when they’re older. Or perhaps certain traits are a liability in youth but an asset in old age.

“Think of the personality traits that lead some people to peak in high school versus later in life,” he explained. “It’s a trade-off.”

But when the team tested this idea, using 37 years of data going back to some of Jane Goodall’s early work at Gombe in the 1970s, they found the same personality traits were linked to high rank and reproductive success across the lifespan.

The findings suggest that something else must explain the diversity of personalities in chimpanzees. It might be that the “best” personality to have varies depending on environmental or social conditions, or that a trait that is beneficial to males is costly to females, the researchers speculated.

But, if that were true, then “genes associated with those traits would be kept in the population,” they said.

Not too many years ago, the mere suggestion that animals have personalities at all was considered taboo. Jane Goodall herself was accused of anthropomorphism when she described some of the Gombe chimpanzees as “bolder” or “more fearful” than others, some as “affectionate” and others “cold.”

Since that time, scientists studying creatures ranging from birds to squid have found evidence of distinctive personalities in animals: quirks and idiosyncrasies and ways of relating to the world that remain reasonably stable over time and across situations.

The lead author concluded that personality ratings for animals have proven to be as consistent from one observer to the next as are similar measures of human personality.

So, what? Many studies have shown that human bullies tend to rise to the top as well. People are attracted to bullies because they are perceived as being “strong” and therefore protective.

Political and corporate leaders who are “strong” attract those that perceive they have been wronged and need someone powerful to right the wrongs.

Interestingly, recent research has shown the genetics of leaders and bullies are very similar—the same cluster of genes seems to predispose people to both be leaders and bullies. This is not to say all leaders are bullies—we are not prisoners of our genes. Personality traits are caused by a mixture of three factors: our genes, our experience in childhood and later, and the context we’re in.

Nobody’s personality is fixed, and we can have one personality in one context and a quite different one in another. We can have one set of traits just after a meal and quite different ones when the last meal was a few hours ago. We can have one cluster of traits in artificial light and others in natural light.

I imagine the same is true of chimps.