If you saw the movie “The Last Picture Show” (one of my top five movies), you’ll remember the scene where an English teacher in a small Texas town, facing a class full of bored students, asks, “What are my chances of interesting you people in a little Keats today?” From their reaction, it was nil.
So I ask: what are my chances of interesting the readers in a little biology today, given the kerfuffle that is going on elsewhere? I’d suggest that we move onto chimps today, in particular, the question of whether, when they kill each other in the wild, such acts are “natural” behaviors versus behaviors tainted by human disturbance, which makes the chimps act “unnaturally.”
But first, if you haven’t looked at the post on birds of paradise yesterday, I urge you to do so. The videos are stunning, and I worry that people might have ignored them to go battle each other on the post after that.
So, chimps. . .. In a new paper in Nature with many, many authors (first author Michael L. Wilson, last author Richard Wrangham; reference and link to free download below), a group of researchers examined all the data on murder in chimpanzees: instances when one member of a species kills a conspecific (remember there are two species: chimpanzees, Pan troglodytes, and bonobos, Pan paniscus, both equally related to us). The researchers’ question was this: when chimps kill other chimps, is that a “natural” behavior? Or does it occur only when chimps are “disturbed” by human presence?
The rationale, of course, is not simply to look at how chimps behave. In a New York Times summary of the paper by James Gorman, one of the authors gives the motivation:
In studying chimpanzee violence, “we’re trying to make inferences about human evolution,” said Michael L. Wilson, an anthropologist at the University of Minnesota and a study organizer.
Well, that’s a bit dicey. After all, chimps are not our ancestors: they are primates that evolved from our common ancestor with the the two species, and they have had just as much time evolving on their own since the split as have humans. It’s not clear that our common ancestor would be warlike and murderous, even if chimps are. After all (as we’ll see in a second), bonobos are not very murderous at all, and yet they’re just as related to humans as are chimpanzees.
What did the researchers do? They combined a ton of data from various field studies—that’s why there are so many authors—and compiled every instance of either known or suspected chimpanzee murder (18 chimp and 4 bonobo communities were studied). They found 152 murders: 58 were observed directly, 41 were inferred from forensic data like bite marks) and 53 “suspected” killings were enumerated by observing disappearance of healthy chimps or suspected deaths after known attacks). All of these were in chimps; only one bonobo was murdered by another, and although fewer bonobos were watched than chimps, that probably reflects bonobo’s general and well-known peacefulness.
The authors then considered two hypothesis for these murders—both of the hypotheses could, of course, operate together.
1. Chimp murder is “adaptive.” That is, it is an evolved trait that increases the reproductive success of the killers in some way. To test that, they looked at three predictions: members of the “eastern” clade should kill members of the “western” clade of chimps more often (presumably because of xenophobia); number of adult males in a group should correlate with more murders (the more males the more murders, since presumably it is the males who murder for reproductive advantage); and higher density of a group, which is said to reflect competition for resources and number of interactions, should also be associated with more murders.
It’s a shame that these aren’t great surrogates for what we want to know: do the killers have more offspring than non-killers? But that would be impossible to know, since the killers are males and you’d have to do paternity analysis on every chimp to see who the father was. Still, I’m not happy with these surrogates for adaptation. I suppose they’re the best the researchers could do given the data, but it makes the paper’s conclusions weaker.
2. Chimp murder is an artifact of human impact. The authors used three measures of disturbance as well: size of protected area covered by a group (the assumption is that smaller protected areas experience greater human impact); whether or not a group was artificially fed by humans; and “disturbance” (an amalgam of five variables including habitat disturbance, human harassment of chimps, hunting, habituation to humans, and elimination of predators [a sign of human impact]).
The results favored hypothesis #1: murder is adaptive. There was little support for the notion that human impact played any role. The authors note this (my emphasis):
Of the 16 models we considered (Table 3), four of the five models in the resulting 95% confidence set included combinations of the adaptive variables; the fifth model included the three human impact variables. The best model included only males and density, and was supported 6.8 times more strongly than the human impact model (evidence ratio = wi/wj = 0.40/0.059 = 6.8). Considering model-averaged parameter estimates22, increases in males and density increased the number of killings; for all other parameter estimates, the 95% confidence intervals included zero (Table 3 and Fig. 2). Excluding one community (Ngogo) that had both an unusually high killing rate and unusually many males resulted in similar values for model-averaged parameters, but only the estimate for density excluded zero from the 95% confidence interval (Extended Data Table 5b; n = 17).
Opposite to predictions from the human impact hypothesis (Table 2), provisioned and disturbance both had negative effects [i.e. reduced killing]; the estimates for these parameters included zero in the 95% confidence intervals (Table 3 and Extended Data Fig. 2b). The highest rate of killing occurred at a relatively undisturbed and never-provisioned site (Ngogo); chimpanzees at the least disturbed site (Goualougo) were suspected of one killing and inferred to have suffered an intercommunity killing; and no killings occurred at the site most intensely modified by humans (Bossou).
Some other fun facts about chimpanzee murder:
- 92% of the killer chimps were male.
- The chimps most likely to be killed were other males and infants (killing someone else’s infant can be adaptive if you subsequently inseminate the mother of the victim
- Victims were usually members of other communities and hence unlikely to be related to the killers
- In killings observed, attackers outnumbered defenders by, on average, 8 to 1. Chimps attack in groups.
The conclusion:
We conclude that patterns of lethal aggression in Pan show little correlation with human impacts, but are instead better explained by the adaptive hypothesis that killing is a means to eliminate rivals when the costs of killing are low.
The implicit conclusion, I think, is that humans are innately warlike as well; that’s the reason why the paper got so much attention.
While I think it’s a good effort, there are problems with measuring disturbance and adaptiveness, though there’s no doubt that chimps kill each other in the wild, and they do it in relatively undisturbed areas. That tells us that chimps probably do murder in natural circumstances, but whether that’s adaptive or not is hard to gauge. (I’m not willing to say it’s adaptive just because it occurs.)
Further, bonobos don’t murder much. They are just as closely related to us as are chimps. Who can say whether the common ancestor was more bonobo-like or chimp-like? So while chimps murder in the wild, this doesn’t say whether our common ancestor, much less early hominins, were genetically warlike. Certainly our ancestors killed each other, and maybe that reflects a genetically conditioned xenophobia, but I don’t think the chimp studies say much about this.
At any rate, the New York Times piece reports some dissent by other scientists:
Robert Sussman, an anthropologist at Washington University who supports the idea that human actions put pressure on chimpanzee societies that results in killings, was dismissive of the paper. “The statistics don’t tell me anything,” he said. “They haven’t established lack of human interference.”
Brian Ferguson, an anthropologist at Rutgers University who has written extensively on human warfare and is working on a book about chimpanzee and human violence, also argued that the measures of human impact were questionable. The study considered whether chimpanzees were fed by people, the size of their range and the disturbance of their habitat. But, Dr. Ferguson said, impact “can’t be assessed by simple factors.”
“I’m arguing for the opposite of the method that’s being used here,” he said, adding that a detailed historical analysis was needed for each site.
If I were a reporter, I would have asked both Sussman and Ferguson to clarify their comments. What does the former mean by saying “they haven’t established lack of human interference.” Where is the interference supposed to be in the least disturbed site? (I’m not saying it wasn’t disturbed, but I’d like more specific criticisms.) And Ferguson’s objection does carry some weight given what I’ve described above, but saying disturbance “can’t be assessed by simple factors” overlooks the fact that five measures were combined into the index of disturbance. And what does he mean by “the opposite of the method used here” and “a detailed historical analysis”? It’s not clear; and that’s probably the reporter’s fault.
Finally, there’s dissent about what it all means for our own species:
Richard Wrangham of Harvard, the senior author of the new paper and Dr. Wilson’s onetime doctoral adviser, is the co-author of a 1996 book, “Demonic Males: Apes and the Origins of Human Violence.” Although the issue is not mentioned in this paper, he argues that chimpanzee behavior “is a reasonable start for thinking about primitive warfare in small-scale societies.” But, he added, “I certainly wouldn’t want to say that chimps have anything much to say directly about what’s going on in Syria.”
But what about the bonobos? Why is their behavior irrelevant? But he’s dead on about Syria, which is due largely to religion, something that chimps don’t have. (You could counter, though, that religion is just a surrogate for “othering,” which prompts an innate xenophobia.)
Dr. Sussman, who is skeptical of drawing connections between chimpanzee and human violence, said, “War has nothing to do with what chimpanzees do.”
Well, what if we’re not talking about organized state war, but simple person-on-person violence? Maybe that could be relevant to what chimpanzees do.
But the whole debate about humans from this paper alone seems futile, because we’re not looking at our ancestors, but species that diverged from our common ancstor with chimps 6 million years ago—and one of those species isn’t warlike at all!
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If you want to see a group of chimps killing a member of their own band (not that common), there is a YouTube video here. But please be warned: it is fairly graphic, so don’t watch it unless you have an interest in how this occurs.
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WIlson, M. L. et al. 2014. Lethal aggression in Pan is better explained by adaptive strategies than human impacts. Nature 513:414-417.
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Oh, my. Makes me glad I didn’t see that until this morning…I hate to think of how my WEIT mailbox would be groaning had I subscribed!
I think, if we’re going to be attempting to make behavioral comparisons with other primates in an attempt to triangulate what our ancient ancestors were like…well I don’t see how much we can really learn with such a small sample of species. Wouldn’t we at least need to perform similar studies of the other Great Apes? Do gorillas and orangutans follow the same pattern? If so, does it also hold up in monkeys, both Old and New World?
If there’s no significant variation across a wide range of primate species, then we can be pretty certain that our own common ancestor with chimpanzees fit that pattern. But if it’s a real crapshoot, then we may have to rely upon a much better fossil record than we’re likely to ever have to be able to conclude anything.
Also, I don’t think anybody contests the fact that chimpanzees have culture, and it’s unquestionable that murder rates amongst humans are significantly affected by culture — just look at all the “honor killings” if nothing else. How do we know that the differences between the different species are a result of genetics as opposed to culture? Would a chimpanzee raised from infancy by bonobos be more or less likely to commit murder, and vice-versa?
b&
Yes and what is the human correlate for chimp society? The closest approximation would be hunter-gatherer groups of which there are few now. Those human societies, however, tended to be nasty, brutish & short (to quote Hobbes) and maybe that more speaks to their circumstances than their nature – it’s hard to tell.
I remember reading of a troop of chimpanzees in which all of the adult males died after eating food that somebody had poisoned. The adult females had to raise the remaining young males, and in the next generation of adult males the rates of rape (which chimps are notorious for) and general violence dropped tremendously.
It might have been a story from “Shadows of Forgotten Ancestors” by Carl Sagan and Ann Druyan, but I’m not sure.
Actually, that episode is from Robert Sapolsky’s A Primate’s Memoir: A Neuroscientist’s Unconvential Life Among the Baboons, and the species in question was baboons, not chimps. http://tinyurl.com/kkugz
The poisoning was not intentional, it occurred because the most aggressive males were scavenging from a garbage dump, and, as I recall, contracted tuberculosis. But in principal the rest of the story is pretty much accurate. For all the particulars I suggest you read the book; its a wonderful book, well worth your time.
Further, bonobos don’t murder much. They are just as closely related to us as are chimps. Who can say whether the common ancestor was more bonobo-like or chimp-like?
Is this true, though? Aren’t bonobos simply more commonly found in unnatural situations than chimpanzees, which could distort the patterns of behaviour they show?
I read some comments the other day (somewhere, can’t find it right now) by someone who’d looked at the tabulated data in the supplements to Wilson et al. and worked out rate of killings per chimp-day observed, at various localities. Observations of bonobos have been orders of magnitude less extensive, and on the assumption that maybe one bonobo death was actually a conspecific killing the rates are not terribly different between the species (if I recall correctly, and if the person whose name I don’t recall had done the calculations right).
Of course, to make an evolutionary argument it’s really necessary to compare rates in gorillas, orangutans, gibbons, and various monkey clades. Lots of follow-up work required, and difficult analyses considering the huge variations in ecology. Wrangham may be predisposed to limit the focus to Pan & Homo with their similar fission-fusion societies (terms of Kummer; Wrangham himself called them ‘party-gang species’ in Demonic Males).
Oh, that was Torbjörn, who copies his comment below. Don’t mind me, carry on!
I (a very slightly knowledgable layperson) think of chimps as the violent ape, bonobos as the sexy ape, and humans as the violent sexy ape.
(All to a first approximation, and with variation, of course)
“I’m not willing to say it’s adaptive just because it occurs.”
I don’t think it’s fair to characterize their position this way. The argument is not that it’s adaptive just because it occurs. The argument is that the precise pattern of results is exactly what you’d predict under the adaptation hypothesis, and that the only known alternative to the adaptation hypothesis, i.e. “human influence,” has been ruled out. Therefore, we should increase our confidence that the adaptation hypothesis is correct.
Yes, it’s possible that the killing behavior is some kind of spandrel, but without a specific proposal of what that spandrel might be and how it can account for the precise pattern of results, such an assertion is untestable. It seems to me perfectly legitimate to claim that the adaptation hypothesis is the current most likely explanation for the behavior.
Sorry, but I wasn’t trying to characterize the authors’ position at all with that statement. I was trying to defuse the common notion that animal behaviors in the wild must perforce be hard-wired by natural selection.
Unfortunately, I think the index of “adaptiveness” is pretty weak, so my confidence in it is only marginally increased by this paper. And yes, I agree that the most likely explanation for the behavior is that it serves a purpose, but whether that is cultural or genetically hard-wired is up for grabs. And “most likely” is a long way from “strongly supported” in this case, at least in my view.
“Culturally hard-wired” traits can be adaptive, too, since it’s the animal’s genetics that allows for that “culture” to take hold of the animal’s behavior. I never understood why “culture” was considered an alternative to adaptive.
I would argue with the logic that the last hypothesis standing wins. Evidence against the human disturbance hypothesis is not support for the alternative adaptive hypothesis. These are not the only options. Ben (comment above) mentioned culture, which could be adaptive in a sense but also not. There are also examples where particularly behaviors reflect maladaptive consequences of cognitive (behavioral) mechanisms that are overall adaptive, but lead to non-adaptive outcomes in some cases. Classic example: avian brood parasites tap into parental care responses in their hosts. Care for offspring (ones own) is adaptive; caring for cuckoo chicks is not.
David, I was wondering if you’re going to ever blog somewhere.
All this seems obvious to me. Killing other members of your species that are not close relatives is advantageous to the “selfish gene” because it eliminates competition for resources and/or mating partners, depending on the situation.
As for comparing humans to chimps vs bonobos, my understanding of chimp and bonobo behavior is that humans are much more like chimps. The first thing I always read about bonobos is that they use sex to resolve conflicts. Thats not what goes on in human groups. At least, not where I work.
This article says that although the human genome is equally similar to chimps and bonobos, certain parts of our genome are more like chimps, while other parts are more like bonobos.
http://www.sciencedaily.com/releases/2012/06/120613133144.htm
It can just as easily go the other way. Who wants to have anything to do with a brutal murderer? How can you trust such an individual? Might well be safest to band together with some others to eliminate the threat — which is exactly how humans wound up with police and justice systems.
In our society, casual violence is detrimental to reproductive fitness. Yes, there are exceptions, including battered spouses…but violent behavior is much more likely to remove you from the “dating scene” and any children you might have will themselves be severely disadvantaged.
b&
“Who wants to have anything to do with a brutal murderer?”
Lots of people. Do you think a gang member, warlord, drug lord, soldier, or mafia hitman is abandoned by his fellows when he shows he will kill?
Females especially often seem drawn to violent males. Heck, serial killers sent to prison for life soon have a clan of female admirers who write them letters, profess their love, etc. Interesting that female serial killers dont get that response. Every genocidal maniac I can think of – Hitler, Stalin, Mao Zedong, Pol Pot, Hussein, etc – all had wives. Ray Rice knocked his girlfriend out cold in that elevator.. and she married him the day after he was indicted for the crime.
“violent behavior is much more likely to remove you from the “dating scene””
Thats true now, but of course human nature evolved before there was police, laws, etc. When we became civilized, we created laws to solve the problem of violent tendencies that natural selection had created in us.
Reading de Waal’s books on chimp behavior, a chimp who kills another chimp in the group does suffer consequences, but the consequences are not usually a big deal, and dont last long.
You do realize, do you not, that all your examples generally are of the most dysfunctional and least productive societies and elements of society? Citing the leaders of the spectacularly-failed states of Nazi Germany, Stalinist Russia, Cambodia, Iraq, and the others goes rather more to prove my point than the contrary, I should think.
b&
No, your point was that nobody wants anything to do with killers, and that thus killing is not evolutionary advantageous, and that point is incorrect. Of course killing has risks, but it’s those on the opposing side, not those on the same side, who generally pose the risk. And yes, killing is generally a tactic of dysfunctional people in this day and age, but we’re talking about evolutionary history. Do you think only “dysfunctional” chimps kill other chimps?
Something else just occurred to me. Chimps have a very long history in captivity. I’d expect there to be records of some sort that could be combed through to look for both chimp-on-chimp attacks and chimp-on-human attacks. Wouldn’t that constitute a very important data point in this sort of analysis? After all, you don’t get any more immersed in human influence than as, literally, an Hollywood actor.
b&
That is a very asymmetric situation though, with the power in the hands of the humans (most of the time). I wouldn’t want to draw any conclusion re relative frequencies out of that.
I think I know who you are linking to, without even clicking. 🙊
They always use baby chimps, never full grown males, they’re too dangerous. So there’s your answer.
My sources here was the BBC article on war in chimps. It seems de Waal was delighted with ‘data, finally’. Since I naively ran the numbers and posted about them here a few days ago, I will morally repeat it:
Chimps have ~ 30/100 000 murders/year*individual; they observed over 1 500 individuals at 18 sites over 400+ observational years. (My lousy estimate from ‘an average’ ~ 80 group size, group sizes from Wikipedia.)
Bonobos, with spotty statistics (4 sites, 100- years, much smaller groups), may be limited to the same number, ~30/100 000 murders/year*individual. They saw 1 potential murder.
Humans had ~50/100 000 murders/year*individual last year unless I’m mistaken. About half of those would be between familiar individuals, IIRC. War and so terrorism has now become negligible, ~1/100 000 murders/year*individual. [Wikipedia figures on total murders, wars and world population.]
The correlation in chimps was not with human ingression as such, but with lack of resources – but I get this second hand from BBC. The researchers seem to think the behavior is adaptable.
Anyway, bonobos are claimed elsewhere [Wikipedia] to have evolved their particular social structure because their habitats are resource rich. So I would guess my estimate of their upper limit on murder rate is high.
TL;DR: Curious how we apes (chimps, bonobos, humans) naively come out with roughly the same amount of murderous aggression (organized or not)!
ADDED COMMENT ON THIS ARTICLE:
If this was the first real data, which BBC’s article seems to suggest is de Waal’s take, I don’t see how Jerry can motivate his claim that “bonobos don’t murder much”!?
My problem is (I am no statistician, mind) that with only 1 observation of murder, and a tentative one at that, can we really constrain the bonobo murder rate at that level? Spotty data should mean it can be much lower but also roughly that of chimp murder rates – or even a few times more.
I’m not so sure, as the paper notes first that “bonobos are consistently found to be less violent than chimpanzees,” and they give two references. hey also give some data:”Controlling for years of observation, chimpanzees had a higher rate of killing than bonobos; this difference was statistically significant for eastern but not for western chimpanzees”. Western chimpanzees show fewer murders than eastern chimpanzees.
The idea that bonobos murder less (if they do) because they live in more disturbed sites doesn’t comport with the one murder the authors know of (it wasn’t a direct observation), which occurred in a site with a low disturbance rating.
Still, I’d claim that this is all of dubious relevance to human violence.
Agreed. My naive analysis is naive, and so I guess my notion will be that the result is “curious” rather than informative.
I would have _liked_ to say “suggestive”, but I’m neither statistician nor biologist.
Actually no, what I did was too lousy to make it to suggestive anyway. Sorry, I’m juggling these comments and dinner…
I think you are reasonable on the point about the low amount of bonobo data. But their society is much more peaceful, day to day, with all that free love that they engage in. That is not a formal demonstration that they murder less often, but it does make sense that fewer motivations to murder goes along with their being fewer murders.
My thoughts kept going back to Steven Pinker’s book The Better Angels of Our Nature. It is interesting to think about this, if chimps independently evolved to be more violent, but I think Pinker already established that it isn’t that much of an open question how early humans did in fact kill each other (his CSI palaeolithic bit in the book).
Jerry Coyne alludes briefly to this fact when he writes above:
“Certainly our ancestors killed each other, and maybe that reflects a genetically conditioned xenophobia, but I don’t think the chimp studies say much about this.”
But this is indeed a hard question, on how does one research the ways violence has evolved, stayed or dwindled in the primate branch.
Oh, minor trivial speculation, I think the main reason this question of chimp violence and it’s “relevance” to human violence is made to appear so profound and controversial is of course the endless see-saw battles of humans being either empty shells filled with the magical ooze of culture’s influence or they are completely robotically hard-wired to obey their gene masters.
To put it in the hyperbolic terms so familiar from debates about evolution and it’s role in shaping humans.
Though I do think “culture” is often used in a bit of a cheating way to “explain” like a panacea human behaviour.
This article seems useful though less so than we could wish.
There is a romantic view of nature in which non-human animals are good (though sometimes violent, as predators) and evil belongs to humans. (This isn’t simply a Christian idea now, whatever its origin.) Therefore, if good chimps murder, it must be humans’ fault. Clearly, that’s not the case.
I think all we can say from this about the genetic basis of murder is: Humans, chimps, and (at a low rate) bonobos murder. Therefore, our genetics clearly allow murder. The great majority of humans, chimps, and bonobos don’t murder. Therefore, our genetics doesn’t require it.
In humans and chimps, murders usually (not always) fall in categories that could assist overall fitness. This might mean there’s a genetic basis for killing rivals, but might equally reasonably (and I think more likely) suggest that there is a genetic (as well as cultural) basis for protecting kin and potential mates who can contribute to our fitness.
Chimps, Bonobos, and Humans:
First, I am not a biologist nor a statistician. However, from what I’ve read, chimps and bonobos are human’s closet living link to our common ancestor. I read the paper (and again I’m not an expert) and I don’t think there is anything in it that would warrant making any predictions about human behavior.
It would seem to me that if you are going to make inferences about humans, you would compare the percentages of chimp and bonobo DNA humans carry and specifically those genes that affect aggressiveness (if they are known?). And then compare rates of homicide between chimps, bonobos, and humans. Only then do I think you could draw “some kind of correlation.” The scare quotes are there because – as Jerry points out – there needs to be a correction for culture, which the paper only considers human interaction with the studied groups and nothing else. I can’t speak to chimp and bonobo cultures, but I can say with confidence that human cultures play a big part on human behavior.
So, I am thankful for the research that was conducted by these biologists (I’m smarter now about chimp behavior then I was before), but as a non-biologist what I got from the research: Chimps are more aggressive and more likely to kill a rival than bonobos, additionally chimps and bonobos are most closely related to us. As a person who probably has the least amount of knowledge of biology as anyone who reads this blog… I already knew those facts. Again, being a non-expert, maybe that study moved biology forward in some way (in which case I would call it a huge success), but it seems to me, that the authors could have held off on publication until they did the DNA work.
Evolutionary theory predicts that lethal violence (among males, among groups, infanticide, and other categories) will be related to mating system, resource distribution, and other aspects of ecology. Making and testing such predictions does NOT require knowing anything at all about what mutations correlate with what behavioural phenotypes. Doing that kind of DNA work is really nothing at all to do with the theory they’re working with, and has hardly been done for any species anywhere.
Plus, ‘holding off’ publishing data on a species that may be extinct in our lifetime would be a bad idea.
Thanks John!
“Evolutionary theory predicts that lethal violence (among males, among groups, infanticide, and other categories) will be related to mating system, resource distribution, and other aspects of ecology. Making and testing such predictions does NOT require knowing anything at all about what mutations correlate with what behavioural phenotypes.”
That makes sense to me as well as not holding off publication when a particular species could become extinct.
However, my overall point (which I obviously failed miserably at indicating that it was my overall point) was that without the genetic evidence, the authors have very little basis to infer anything about human behavior based on their study (hey, Magpies can be really violent, what evidence would be required to show that their territorial violence is related to human violence?). Had they published the study without the inferences to humans, I wouldn’t have a had problem with it (although, as I a said, as non-expert it didn’t tell me anything that was not already common knowledge amongst non-experts).
That primates, especially males, can be violent within the group is consistent with with their anatomy. Many (most?) male primates are larger than females, with proportionally larger canines. These are used to intimidate and attack others in their group, and to attack other groups. I would not expect it to be controversial that this is the result of sexual selection where male success is proportional to how effective they are at dominating other males, and in winning and holding new territory and resources for the group and for protecting the group from predators. It would be hard to parse this out from success by murder specifically, but murder would ride alongside selection for war amongst primates. Even male mice kill each other and perform infanticide pretty often.
The earliest fossil record of hominins (upright walking primates) starts off early with an interesting twist. The best known of these early species is Ardipithecus who already had remarkably small canines. The speculation here is that early in hominin evolution there was a change in social structure where reproductive success depended more on forming long term pair bonds, and on being able to be a carer and nurturer of young. By the rule of ‘use it or lose it’, canines would be expected to shrink in size.
Don’t chimps have natural predators? Leopards in jungles, lions at the edge of the savannah along with pythons and crocodiles? I would assume chimps run into other animals, large and small.
I don’t see why human predation or other human interactions would be special in terms of precipitating chimp murder or other reactions compared to the chimps interaction with other dangerous (and not so dangerous) species.
Yes. I think they are in special danger when young, which is one reason why males are big. One of their roles is to be a protector of the group.
Hey, bonobos make love, not war.
I find this subject fascinating. I think it depends on how you might define “war”. If war is aggression to get resources, I wonder if it increases with the level of intelligent and the ability to conceive of the future, foreseeing a lack of them and conceiving of the need to get more.
Full disclosure: Not a biologist just an enthusiastic end-user.
Seems to me that there is a false dichotomy between “adaptive” and “caused by human contact/intervention.”
Why cannot the chimp on chimp violence be maladaptive with or w/o human intervention. Humans have adaptive as well as maladaptive violence — why not chimps? It makes evolutionary sense for a human to kill a sexual rival; not so much to kill because the voices in your head say “kill, kill, kill” but that happens a lot. Maybe chimps have mental illness that we cannot detect or understand. Maybe it’s a result of interaction with humans or maybe it would have happened regardless of our presence. Maybe it’s too many fermented bananas. Or his daddy didn’t take him termite fishing.
Yeah, chimps can have a dark side too.
To anyone who enjoys reading about chimp-on-chimp violence (And who doesn’t?), I’d like to recommend Sarah Blaffer Hrdy’s Mother Nature. Clear and beautiful prose, and (as far as I can tell as a layman), sound science.
I was also perusing an entry on the web about the various chimps that Jane Goodall followed for years. The site briefly described each individual, who their mother was, their personalities, and the major events in their lives.
It was really a long list that was rather dense with violence. There were even female chimps that were serial killers. They would systematically hunt down and murder infant chimps in their own group. Alpha males who were toppled brutally by coalitions of other males, only for the new alpha to be overthrown in a couple years. The occasional war and murder from neighboring groups, etc. Brutal lives, really.
I remember an excellent french broadcast “Rendez-vous en terre inconnue” where a french artist has to be immersed in the life of a “first people” tribe as far as possible remote from western influence. In this particular case it was a popular singer, Zazie, meeting a tribe of New Guinea’s hunters-gatherers, the Korowai. These people, quite decent, kind, friendly, helpful and… well, civilized, explained her that they built their houses high in the trees, and clear every other tree around the house, for fear of an attack by neighbor groups. And they plainly state that if they meet some foreigners around, and if these foreigners don’t show mutually agreed signals of peace, like talking wery loudly about wanting to meet friendly neighbors, they will be killed immediately. They plainly understand and admit that this is reciprocal, and that they had some relatives killed recently. It’s just the normal way to go. And, while they are perfectly conscious that their way of life will soon disappear through contacts with the outside world, school and trade (they are neither stupid nor unaware of what’s going around), most of them don’t want to leave it.
I think that some intergroup violence is deeply ingrained in our species, and that this case is not very different of what was observed in Pan troglodytes groups. And for the bonobos, I would wait for a bit more data before to reach any conclusion.
And when Robert Ardrey said this more than 50 years ago in his African Genesis, he was villified and described as an amateur. But Ardrey’s views and conclusions were not grabbed out of thin air. It was based to a large extent on the works of the Afrikaans writer Eugene Marais who could well be described as the first observer of apes in their natural state. Marais work was later published in English in The Soul of the Ape, but it was known widely by Afrikaners in SA. (Marais’s other marvellous work was The Soul of the Ant)
Interestingly enough, I was just reading Ardrey’s work (again) when the BBC report came along. Confirmation at last, but alas no belated recognition and/or apology!
TH
Pretoria.
Yeah, but Ardrey was an amateur in the sense that he didn’t just report the ideas of professional anthropologists but put his own spin on them, and had a quite non-scientific (and often wrong) understanding of how evolution works (which was typical of the time, even among professionals!). I read his books (and Marais’, and Morris’ and Lorenz’) several times from when I was about 12, and gained some very strange ideas about ‘genes’ that took years of other reading to shake off. I would recommend those books to anybody, with caveats.
I’m in full agreement with you Jerry on this and on your later comment about it having to do with person-on-person violence.
AIUI, Chimpanzee violence is pretty similar to the sort of violence humans practice in primitive cultures: aggressors try and minimize the risk to themselves by using ‘unfair’ violence. I.e., night raids. Surprise attacks. Overwhelming odds, or for one-on-one encounters, only attacking individuals noticably weaker than you.
Based on this and the fact that humans generally don’t practice any of the sexual bond-making acts that make Bonobos so unusual, leads me to tentatively think that our ancesters were probably more like chimps than bonobos. But whether that’s right or wrong, I am not surprised at all with the results of this study or the types of violence most often seen in chimps.
Our scientific understanding of chimpanzees has undergone some rather dramatic changes in a relatively short time. For example, from page 12 of “Man and Aggression,” a collection of Blank Slater essays edited by Ashley Montagu and published in 1968, “The field studies of Schaller on the gorilla, of Goodall on the chimpanzee, of Harrisson on the orang-utan, as well as those of others, show these creatures to be anything but irascible. All the field observers agree that these creatures are amiable and quite unaggressive, and there is not the least reason to suppose that man’s pre-human primate ancestors were in any way different.”
Worth reading in this context are Sarah Blaffer Hrdy’s “The Woman that Never Evolved”; “Mother Nature: A History of Mothers, Infants, and Natural Selection+; and especially “Mothers and Others: The Evolutionary Origins of Mutual Understanding.”
I believe that sex and aggression are deeply linked behaviors: it’s easy to forget that for an adult female animal to allow an unrelated adult male animal into the physical proximity necessary for the reproductive act, an entire set of defense and territorial instincts must be resisted or “put on hold” (we humans, in most cases, have complex sets of “ritual-type” behaviors that prepare the way for the relaxation and receptivity of the female, although the list required might be pretty short in a singles bar). For the male, the actions needed to get close to a “strange” female often involve many of the same behaviors involved in hunting prey and care must be taken as, if the female is not receptive for whatever reason, the attempt may end up in serious injury or even death for the male. The sex act itself is often accompanied by growling, hissing, biting and scratching (why do most male porn stars feel it’s necessary and “sexy” to smack their sex partner on the ass? Aren’t they supposed to be making “love”?); it’s not unusual for wounds to be sustained in the process of mating.
Therefore I propose that the “chimp-on-chimp” killings emerge from a “complex” of motivations: territoriality; food and water source availability and access, and the “sex-aggression” chain of behaviors sparked by phermones from “strange” females which draw the adult males close enough to the “strange” males that “hunting-type” aggressive behavior takes over, with the chimps operating in groups to kill just as they do when catching monkeys. It doesn’t seem to happen often, but I have read of chimp groups completely annihilating other groups, male AND female, over a period of time; I think it’s possible that what’s occurring in that case is a failure to be able to “dial back” the aggression to that of the mating level, like a soldier who continues to shoot civilians after all the enemy troops are dead.