Bonobos: the self-domesticated ape?

By Ed Yong | January 25, 2012 12:41 pm

The two apes above might look very similar to the untrained eye, but they belong to two very different species. The one on the right is a bonobo; the one on the left is a chimpanzee. They are very closely related but the bonobo is slimmer, with a smaller skull, shorter canines and tufts of lighter fur. There are psychological differences too. Bonobos spend more time having sex, and playing with one another. They’re less sensitive to stress. They’re more sensitive to social cues. And they are far less aggressive than chimps.

Many years back, a young researcher called Brian Hare was listening to the Harvard anthropologist Richard Wrangham expound on this bizarre constellation of traits. “He was talking about how bonobos are an evolutionary puzzle,” recalls Hare. “They have all these weird traits relative to chimps and we have no idea how to explain them.”

But Hare had an idea. “I said, ‘Oh that’s like the silver foxes!’ Richard turned around and said, ‘What silver foxes?’”

Hare meant these silver foxes.

They were the work of Russian geneticist Dmitri Belyaev. In the 1950s, Belyaev managed to breed domesticated foxes in a startlingly short amount of time. He simply selected for the nicest individuals, breeding those who were least aggressive towards their human handlers. Twenty generations later, and foxes that would once have snarled at human handlers would wag their tails instead.

But it wasn’t just the foxes’ temperaments that changed. The domestication process also warped their bodies. They ears became floppier, their tails curlier, their canines shorter, and their skulls smaller. They developed white patches on their fur. Their physiology changed too: they became less sensitive to stress and more sensitive to social cues.

They developed a suite of features known as the “domestication syndrome”, which you can see in domesticated animals from dogs to guinea pigs. This set of traits, both physical and psychological, seem to appear as a package. And it’s the same set that Hare recognised in the bonobo.

Now, in a new review, Hare puts forward the hypothesis that bonobos are “self-domesticated” apes. By naturally selecting for a ‘nicer’, less competitive ape, evolution has forged an animal with the same cluster of traits that humans have pushed onto other species.

I’ve written about Hare’s idea at Scientific American, so head over there for the full story, including why and how exactly this would have happened. For now, I want to highlight two bits of the work.

First, a nice quote from Greger Larsen – a domestication researcher – who sums up why Hare’s idea is interesting: “People have been thinking about domestication as a human-centered thing: purposeful, directed, something we do to animals. But what Brian says is that this process, which we imbue with all this human-centric meaning, is something that takes place in nature. That’s super cool.”

Second, Hare was refreshingly candid about the fact that this is a hypothesis, and open to criticisms (and you’ll find some from Frans de Waal at the SciAm piece). He himself identified three to me. First, it’s not clear if the ancestor of chimps and bonobos was more chimp-like than bonobo-like. Second, he’s making educated guesses about how the self-domestication happened because we know very little about the bonobo’s environment, both current and ancient. And third, you’d ideally want to test the self-domestication hypothesis in other species too, rather than just bonobos and chimps.

Still, it’s a fascinating idea and one that will no doubt be tested in the future. As Hare says: “The goal of the paper is to generate a lot of enthusiasm and excitement about studying bonobos,” he says.  “Even scientists don’t even know they exist and that’s horrible.”

Reference: Hare, Wobber & Wrangham. 2011. The self-domestication hypothesis: evolution of bonobo psychology is due to selection against aggression. Animal Behaviour  http://dx.doi.org/10.1016/j.anbehav.2011.12.007

Images by Pierre Fidenci and Ikiwaner; silver fox from Cornell

Comments (24)

  1. Physicalist

    The one on the left is a bonobo; the one on the right is a chimpanzee.

    Sure you’ve got that right? I’m not an expert, but I’d guess it’s reversed.

  2. Sigh. Yes. Fixed. Oy.

  3. Very interesting. I don’t know why people keep claiming there are places where food is consistently plentiful relative to the animal population – simple Malthusianism states the animal population will increase to the level of scarcity. So Hare’s idea that plentiful food south of the Congo provides the evolutionary mechanism doesn’t work for me.

    So here’s another possibility – Dawkins’ idea of memes and memetic evolution. Bonobos are smart enough to have a culture. The cultural idea of cooperating, especially between unrelated females, could drive the domestication, with “natural” evolution being effectively a result of artificial selection by females choosing nice males for increased sexual access.

    The fact that bonobo society is dominated by unrelated females over related males strongly suggests to me a cultural and memetic component to the species behavior, and as Hare suggests, some physical aspects.

  4. Ed – I read somewhere ( or saw it on PBS) that one of the traits of domestication of the dog from the wolf was that the dog can look you in the eyes where the wolf cannot. Is this true? And if so is that the case of the Bonobos ? Can they look you in the eye?
    Regards… Jim

  5. Daniel Gaston

    A few years back I read a lovely piece on Bonobo’s but I cant, unfortunately remember the author or title. It MAY have been in SciAm but again, my memory is fuzzy. What I do remember reading (either the author or person whose work the article was about) had been doing wild Bonobo observations and in many ways they conflicted with the “resolve all our disputes with sex, peaceful hippy-ape” narrative about Bonobos that everyone liked to talk about. And that was because many of the observations made are done on captive bonobo populations and not those in the wild.

    The researcher put forward that wild bonobo’s, while generally less overtly aggressive, actually seemed a lot more high strung than wild chimps. And while their social structure is matriarchal it isn’t non-violent by any means. Subordinate males being maimed by the leading females was not uncommon.

    These ideas seem interesting but I’d like to see just how stark some of the differences really are if we only look at wild observations. Humans also became more gracile during evolution….

  6. Hey, I thought we were the self-domesticated ape!

  7. Daniel, here it is:

    http://www.smithsonianmag.com/science-nature/10022976.html?page=1

    I think again we’re talking Malthus here. Bonobos have to control territory and exclude others through violence because otherwise they’ll starve. That doesn’t stop them from being “domesticated” relative to chimps though.

  8. Daniel Gaston

    Brian, that is the article, thanks.

  9. Yacko

    So, which way is the human race going?

  10. Kappy

    Are the silver foxes considered legitimate pets? I’m not big on exotic pets, but having a fox would be cool, assuming they were legitimately domesticated like a dog or cat.

  11. I think Hare’s theory draws on Wrangham’s explanation of speciation between the two members of the the Pan genus. Food isn’t more abundant per se in the bonobo habitat but the bonobos evolved to have a less specialist diet so were able to occupy the ecological niche previously filled by the gorilla and feed upon terrestrial herbaceous vegetation when fruit was scarce. This released them from competition compared to the chimpanzee who still shared their habitat with gorillas.

    White F.J, Wrangham R.W (1988) Feeding competition and patch size in the chimpanzee species Pan paniscus and Pan troglodytes. Behaviour. 105, 148–164.

  12. Toos

    Something like this, IS found in another species living in the wild: the Forest Troop of baboons.
    http://animalwise.org/2011/12/29/peace-on-earth-good-will-towards-baboons-and-humans/
    describes it [and gives the source publication]. The most agressive adult males of this troop all died suddenly at the same time [by bad food they took]. Since then, a much more peacefull culture lasted in this troop, with an important role for the adult females keeping it that way.
    For changes in looks it’s way too short, íf this would occur. But the change in behaviour seems striking resembling to me to this chimp-bonobo-story.

  13. muhr

    “Bonobos spend more time having sex”

    i don’t think there is agreement on that among primatologists. chimps and bonobos may have the same amount of sex, but bonobos do so over a females entire reproductive cycle whereas chimps concentrate it in the ovulatory phase.

  14. Toos – ironically, de Waal wrote up that story in a book he did on primates that argued that primates possess culture (ironic because he doesn’t buy Hare’s argument).

    I think what it proves is that cultural components of primate biology is so strong that explaining things via simplistic natural selection arguments don’t always work – culture can be a cause as well as effect of primate biology.

  15. Toos

    Brian, I can’t exclude that such a change in culture couldn’t cause change in looks, though perhaps only under certain circumstances [like isolation by that river]. In this case, culture could be the cause of “self-domestication”-effects in appearance. What I don’t see is, why the one should completely exclude the other. The more because Hare doesn’t say at all it would have happened frequently.

  16. @Brian, cultural or behavioural components of primate biological variation may indeed be extremely strong, but this does not mean that they are not affected by natural selection. Natural selection is able to act on any type of inherited variation that influences reproductive success, whether it is behavioural or morphological .

  17. The body language in the apes photo says it all–I don’t know if the poses are deliberately chosen or characteristic. Now if only humans could self-select for niceness.

  18. chris y

    You could, if you wanted to write a just-so story about it, argue that there’s a correlation between self-domestication and changes in appearance in the other well attested case, the hominins. H. sapiens, neanderthalensis, and to a lesser extent earlier Homo have a lot of neotenous features compared to Australopithecus, Paranthropus or Pan. And neoteny seems to be common trait in many domesticated species.

    After all, there has to be some reason why we’re such weird looking apes; I’m sure somebody could get a paper in an Ev. Psych. journal out of it.

  19. Pam

    Robert Sapolsky studied baboons and reported on the troop that lost all its dominant males to disease (contracted from a human garbage dump’s contaminated meat). He was actually studying the biology of stress at the time. Ten years later (I believe) he revisited the troop and discovered that a matriarchal dominance had reduced the aggression among males in the tribe. This may be the source of the link Toos mentions in #12. Here is a you-tube video link (please ignore the unseemly and impertinent diatribe in the comments): http://www.youtube.com/watch?v=QZcTvFqzxA0

  20. @Chris, there are already a few papers that argue humans are self-domesticated apes, or atleast that our sedentary lifestyle has caused changes similar to those in domesticated animals. It depends a lot on how you define domestication.

  21. Nicholas

    Long ago, before World War II, German anthropologist had an idea of human evolutionary development as basically a process of domestication. This is quite similar.

  22. Alex, I agree what hypothetically happened with bonobos is by definition natural selection in that there’s a genetic effect and wasn’t caused by humans. What I’m suggesting may have happened though is that the cause isn’t

    terrestrial food > cooperation a more viable strategy > cooperators flourish > genetic mutations promoting still more cooperation/domesticity get favorably selected

    but instead

    cooperation meme originates > outcompetes domination/intra-group violence meme in the memetic space of bonobo brains > cooperating females sexually select cooperating males > genetic mutations promoting still more cooperation/domesticity get favorably selected

    In the second scenario, the process is strengthened if terrestrial food somehow promotes cooperation, but the scenario doesn’t require that to be the case. The spread of the meme could be a sufficient condition to initiate the genetic change.

  23. Kate McWilliams

    For those looking for a slightly less scientific take, but with a lot more sex, I recommend the Bonobo Handshake by Vanessa Woods.

  24. Good call. Woods is married to Hare ;-)

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