A Blog by Ed Yong

Chimpanzees murder for land


Between 1998 and 2009, John Mitani witnessed 18 murders firsthand, and found circumstantial evidence for three more. But no police were ever called, for these killers were all chimpanzees, from the Ngogo community in Uganda’s Kibale National Park.

Chimpanzees are highly intelligent animals, capable of great acts of empathy, technological sophistication, culture and cooperation. But they can also be murderers. Groups of chimps, mostly male, will mount lengthy aggressive campaigns against individuals from other groups, attacking them en masse and beating them to death. Their reasons for such killings have long been a source of debate among zoologists, but the aftermath of the Ngogo murders reveals an important clue. After the chimps picked off their neighbours, they eventually took over their territory. It seems that chimps kill for land.

The vast majority of these murders were carried out by groups of Ngogo males on patrol. These patrols are stern, single-file affairs. Males march along the borders of their territories, scanning for other chimps and neither feeding nor socialising. They monitor the northeastern part of their territory with particular fervour and indeed, 13 of their 21 kills took place here.

Of these victims, 4 were adult males and 9 were youngsters. That may seem like a small number, but for chimps, these are severe losses. At the hands of the Ngogo attackers, the northeastern community was experiencing death rates that were 23 to 75 times higher than those observed in other groups of chimps. They were even higher (by around 5 to 17 times) than the death rates due to violence between groups of human hunter-gatherers.

It’s clear that the Ngogo chimps are skilled at waging war against their neighbours and the exceptionally large males in their number probably contribute to their aptitude for violence. And because of their aggressive tactics, they have increased the size of their territory by some 22%, expanding into the northeast area that their neighbours once called home. With murder came new real estate to colonise.

Mitani’s observations back up other anecdotal evidence from other parts of Africa. In Gombe National Park, the Kasekala community of chimps took over the territory of the neighbouring Kahama clan after a series of fatal attacks. But the former community actually splintered off from the latter some time previously. Elsewhere in the Mahale Mountains, one group of chimps annexed the territory of another. All the males in the latter group mysteriously disappeared, but no murders were ever directly witnessed.

In contrast, Mitani found clear and direct evidence that the Ngogo chimps killed off their rivals and commandeered their land. These observations don’t rule out the alternative ideas that the attacks were motivated by a desire for more mates. After all, more acreage could attract more females into the group or improves the chances of existing members. But Mitani’s observations do rule out at least one idea behind chimp aggression – that it’s a side effect of humans. Some zoologists had suggested that by providing food to wild chimps, we were instigating conflict between them, but that’s clearly not the case in Ngogo.

Much of this behaviour might seem familiar, for it has poignant echoes of human warfare. After all, we also kill each other over resource. Richard Wrangham, a primatologist from Harvard University, has suggested that understanding the reasons behind chimp violence could help us to understand and address “the roots of violence in our own species”. Even so, Mitani is very careful about drawing an analogy between chimp and human aggression, given the myriad of reasons that humans have for waging war.

Chimp expert Frans de Waal appreciates his caution. He says, “There have been claims made in the past that since chimps wage war and we do as well it must be a characteristic that goes back 6 million years, and that we have always waged war, and always will.

“There are many problems with this idea, not the least of which is that firm archaeological evidence for human warfare goes back only about 10-15 thousand years. And apart from chimpanzees, we have an equally close relative, the bonobo, that is remarkably peaceful. The recent discovery of Ardipithecus also adds to the picture, as the suggestion has been that Ardi was relatively peaceful too. The present study provides us with a very critical piece of information of what chimpanzees may gain from attacking neighbours. How this connects with human warfare is a different story.”

Reference: Current Biology; citation tbc]

Image by Caelio (does not depict a chimp kill)

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14 thoughts on “Chimpanzees murder for land

  1. Seems like Laelaps’ recent post on apex and mid-level predation is relevant here. Apex predators wage “war” on the competition and the result is making the territory more available for the victorious apex predator.

    Seems like you are making an awful lot out of the coincidence that these are the same species. If anything, the more parsimonious explanation suggests that they don’t particularly view members of other chimpanzee troops as anything special relative to other competing species. thus “war” is vastly overblown.

  2. One of Wrangham’s earlier papers on chimp violence pointed out that while intraspecific killing has been observed in many other species (infanticide, dyadic competition for mates, even coalitionary violence), it is exceedingly rare to see premeditated raids into neighboring territories. Because this is seen in humans and many chimp troops, it is somewhat tantalizing to think this may be an ancient behavioral pattern. It might not qualify as full-blown ‘war,’ but there seem to be hard-to-ignore parallels.

  3. It must be one of the most difficult jobs in the world to observe animals killing one another and not interfere, especially when youngsters are at stake. On the other hand, I live right outside Washington, D.C. where there is inexplicable gun violence nearly every night in certain neighborhoods — usually over turf. I think turf can refer to land, possessions, food sources, mates (or the right to mate, or self-esteem.

    The difference between chimps and humans, though, is that we supposedly have higher reasoning abilities which enable us to make different choices than they do.

    Yeah, right.

  4. Wow! Just like people! It reminds me of the drug dealing neighbors scrapping when they step on eachother’s customer turf.

  5. Yep exactly like humans, It’s interesting to see how we’ve evolved to use land as a form of currency / power. These innate traits are still distinguishable in man today however much we hate to relate.

  6. “It makes no difference what men think of war, said the judge. War endures. As well ask men what they think of stone. War was always here. Before man was, war waited for him. The ultimate trade awaiting its ultimate practitioner. That is the way it was and will be” (Cormac McCarthy, Blood Meridian).
    Unpleasant, pessimistic, and true

  7. Regarding war, I stress again that the authors, de Waal, and I are all of the opinion that this doesn’t say anything about the nature of human warfare. Humans war for all sorts of reasons. Chimps, thus far, are known to kill each other to expand territory. Drawing analogies isn’t quite warranted here.

    Also, for interest, I tried contacting Richard Wrangham for his take on all of this but, and not for the first time, he has declined to comment.

  8. Ardi was peaceful? And the evidence for this is… what? That there were no obvious signs of violence among the sparse bone fragments of a dozen or so individuals? Give me a break.

    (I’m not saying Ardi was violent, I’m saying we don’t know. De Waal has some serious ideological axes to grind in these debates and it shows).

  9. “…archaeological evidence for human warfare goes back only about 10-15 thousand years. ”
    I’m wondering why this would be an argument against the hypothesis. I don’t think they’re assuming we were peaceful for the other 190 thousand years right? There might not be a way to find out if we were using extremely primitive weapons like rocks.

  10. I totally agree with the last two comments – given the fragmentariness of fossil record and paleoarcheological finds we just can’t tell whether our ancestors and cousins were more like bonobo or more like the chimps of this study

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