The Sciences

Are We Hardwired to Kill?

The IntersectionBy Chris MooneyMay 28, 2010 5:37 PM


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This is a guest post from Vanessa Woods, author of the new book, Bonobo Handshake. Vanessa is a Research Scientist in Evolutionary Anthropology at Duke University and studies the cognition of chimpanzees and bonobos in Congo.

We like to think that murderers are psychopaths, with some kind of abnormal psychology that would never appear in us, or someone we know. And yet most of us think we would kill in certain situations, like if we were at war, or someone was about to kill a person we loved. How 'natural' is this instinct in us, and can we ever obliterate it completely? In my new book, Bonobo Handshake, I talk about lethal aggression in one of our closest relatives, chimpanzees. Chimpanzees and humans have a lot in common when it comes to killing:

#1 Killers are mostly male. Though female chimpanzees can participate in killing, usually the killers are males. In humans too, the FBI reported in 2005 that 89% of killers are male . #2 Males usually attack when the ratio is 3:1. Wrangham and Wilson reported that both chimpanzees and young men in gangs attack when they outnumber their victim 3 to 1 or more. The reason for this? This is the minimum number that can safely overpower a single victim. #3 The murder rate between chimps and humans is the same. Before we had inventive weaponry that could kill thousands with the press of a button, humans lived in hunter gatherer groups where we lived off the land like chimpanzees. Watts et al, reported that in these societies the homicide rate in humans and chimps is about the same.

#4 We kill for the same reason. Most of the killing is done over females, enemy males, and territory. Think of all the mass wars. Despite the hype of liberation and democracy, what were they really fought over? Scary how much we have in common. Luckily, we also have a lot in common with our other closest relative, the bonobo. Bonobos, like us, can be extremely cooperative and tolerant. Bonobos don't kill each other, and they aren't particularly violent. The key in bonobos seems to be tolerance. In our 2007 study

, we found that tolerance makes bonobos more cooperative than chimpanzees. We've also found that physiologically, bonobos have a very different response to chimps in potentially tense situations. When there is only one pile of food, bonobos experience an increast in cortisol, a stress hormone, while chimpanzees have a spike in testosterone. This means that when there's potential for trouble, bonobos get stressed and chimps get ready to fight. These phsyiological changes aren't something bonobos or chimps can control. But as humans, we need to figure out the situations where we are more chimp than bonobo and correct for our behavior. For instance, during recessions, where resources are tight, historically we see a crackdown on immigration (like the Arizona immigration strategy

). Correspondingly, if you want to see the murder rate go down, you have to figure out when murder is most likely to occur (again, over females, attacks on enemy males, and territory). People get freaked out when you talk about a biological basis for aggression. But until you take ALL the factors into account, we're going to keep making the same mistakes over and over again. *My new book

Bonobo Handshake is out now. It's available on Amazon, or through my website

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