Did conflict drive the evolution of the human brain?

Recent research claims that we evolved big brains to win in any conflict with our neighbors; but does this claim hold water?

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Over the course of human evolution our brain has increased dramatically. 7 million years ago our brain could’ve easily fit in a coke can; now you’d struggle to squeeze it into one of those giant “sharer” bottles of pop1. Obviously this dramatic increase in intelligence has granted our species many benefits; which has scientists fascinated. Which of those advantages drove the brain’s evolution? Researchers have come up with several theories and it’s become increasingly apparent that no single one is correct. Our big brains appear to be the result of many evolutionary forces operating on us.

But have we overlooked one factor entirely?

That’s the contention of a researcher from Australia, who recently published research arguing that conflict was one of the key forces driving the evolution of primate intelligence. He examined how much the territory of groups overlaps with one another in more than 100 primate species; which he then compared to the brain size of these species. This revealed there was a striking correlation between the two, with groups that overlap a lot tending to have larger brains than those primates who live in groups which don’t overlap2.

He hypothesised that the key factor here was the conflict that would ensue from having overlapping territories; prompting an evolutionary arms race amongst neighboring groups2. Chimpanzees, for example, often have incredibly violent “border wars” with neighboring chimps; often leading to one group being completely wiped out3. It’s easy to see how success in these conflicts can be paramount to survival, and how large brains could lead to success.

The correlation between group overlap and brain size identified by the research

The correlation between group overlap and brain size identified by the research

In fact, it’s so easy to see you might be asking why has nobody thought of this before? And they have. The unique thing here is the focus on conflict between groups. Many researchers have previously argued that deceit and conflict amongst members of the same group as they try to climb the social ladder may have been a driver of intelligence4. Others have suggested that large brains help us live in large groups, helping us search a wider area for food and better defend that area against others5. Conflict between groups hasn’t really been considered as a primary factor by itself before.

But as I said at the start of the article, no factor should be considered by itself. The evolution of our big brains was the result of many forces acting upon us. Where does conflict rank in all that? Was it really that important?

And that’s the big problem with this new research. It makes no attempt to establish how important conflict was in brain evolution. No comparisons are made to any of the other known forces – like group size – to establish that it was one of the primary factors driving the growth of our brain2. And it’s not like that’s even asking a lot; a lot of other research does make such comparisons to establish the force they’re looking at is important5. That’s missing here. On top of that, this paper uses a relatively uncommon metric of brain size making it hard to perform such a comparison after the fact. It’s not as though we could just compare the raw data and figure out which was more important; one data set has to be converted first. And it’s not exactly an easy conversion either.

The research into group size, for example, compares the correlation between brain size and group size to the correlation between brain size and many other factors; establishing group size is the most important factor of the bunch

The research into group size, for example, compares the correlation between brain size and group size to the correlation between brain size and many other factors; establishing group size is the most important factor of the bunch

There’s also the fact that at no point does the research establish that border overlap = conflict. Bonobo groups, for example, overlap with one another quite extensively yet they live together relatively peacefully6. And whilst chimps do have violent border wars3, their degree of overlap is one of the smallest identified amongst apes in this research2.

So yeah, conflict was one of the factors that drove the evolution of primate brains. We just have no idea how significant a factor it was. And you also have to assume that border overlap = conflict. Now, science might be a field of caveats and uncertainty, but there’s just too many unresolved issues here. Until they’re taken care of I’m not sure we can really attribute much of primate intelligence to violence.

So look on the bright side: your ancestors weren’t as awful as you thought.


  1. Boyd, R., & Silk, J. B. (2009). How Humans Evolved. WW Norton & Company, New York..
  2. Grueter, C. C. (2014). Home range overlap as a driver of intelligence in primates. American journal of primatology.
  3. Manson, J. H., Wrangham, R. W., Boone, J. L., Chapais, B., Dunbar, R. I. M., Ember, C. R., … & Worthman, C. M. (1991). Intergroup Aggression in Chimpanzees and Humans [and Comments and Replies]. Current Anthropology, 369-390.
  4. Byrne, R. W., & Whiten, A. (1989). Machiavellian Intelligence: Social Expertise And The Evolution Of Intellect In Monkeys, Apes, And Humans (Oxford Science.
  5. Dunbar, R. I. (1998). The social brain hypothesis. brain, 9(10), 178-190.
  6. Kano T, Mulavwa M (1984). Feeding ecology of the pygmy chimpanzees (Pan paniscus) of wamba. In The pygmy chimpanzee : Evolutionary biology and behavior (Susman RL, editor). pp 435

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21 thoughts on “Did conflict drive the evolution of the human brain?”

  1. Wendy says:

    E O Wilson makes the point that altruism among members of the same group and selfishness pertaining to other groups, which can lead to conflict, is the driver of social evolution. It makes sense to me.

  2. welikehumans says:

    I assume they are looking at current population and overlapping territories? Now days territory size would be more limited due to human activity, putting increased pressure on species to fight over what territory is left. During the early evolution of our ancestors, it would seam that opportunities to expand territory or move would be greater. Why risk getting killed in a fight when you can just move, which it seems like, at times, is what they did.

  3. brianrudze says:

    Did they even state a correlation coefficient? This seems like another example of science being done by the non-scientific (officially degreed or not).

  4. Wyrd Smythe says:

    Don’t all animals exist in a state of conflict?

    1. Adam Benton says:

      The conflict for resources drives us all

  5. Andre Salzmann says:

    Yes,andh ow come Erectus stayed around with such a small increase in brain size and the Neanderthal and Sapiens experienced such extravagant development. Our warlike, barbaric nature ?

  6. Cyril C. Grueter says:

    I never said it was inter-group conflict per se that drives encephalization; home range overlap is the variable of interest here which does not only measure conflict potential, but may rather be seen as a measure of socio-spatial complexity at a larger scale…

    1. Jeff/neighsayer says:

      . . . so, conflict, affiliation, and every possible shade and combination between that’s what’s so complex, so hard to sort out, right? In the border zone as well as everywhere else, but yes, a little more life and death at the edge of town, more important in gene spreading and survival than between ourselves at home. I like that if it’s what you’re saying – especially because it leaves room for me and my pet theory too.


  7. martin says:

    How does an arms race end? Aggressive impulses will increase until they reach a line where they become self-destructive (what other mechanism could control it?). Stepping beyond this line means risking extinction – remaining below it means risking defeat in battle. So survival becomes a matter of how close a culture can court this line. What happens next? How about a strategy that will enable a culture to move beyond the line. Can excess aggression be neutralized by building a pyramid, or a cathedral? Does music serve this purpose? We’re told it has “charms to sooth a savage breast ” Wow, we now have a possible evolutionary reason for the existence for music. But will this mean that more aggression can be accommodated? I think I spot a red queen!

    1. Adam Benton says:

      It doesn’t necessarily have to be come self-destructive, the aggressive ones could just wind up being outcompeted by others. Perhaps because circumstances change.

    2. Jeff/neighsayer says:

      “Aggressive impulses?” Is this some sort of first cause? I think there’s more to it. Humans have a level of . . . OK, “aggression” that goes beyond animal impulse, certainly that is sustained far beyond “impulse.” I think we kind of create ourselves in that image.

  8. Jeff/neighsayer says:

    first thing that jumps out at me is this – greater propensity to war and violence of course means smaller overlaps in territory, that’s the point of borders and border patrols, isn’t it? So less overlap means the opposite of less conflict: a spirited border defense insures firm borders and large shared zones would indicate some degree of peace between groups, no? So that part of the reasoning is probably backwards.

    Second, stress and conflict come from within and without your group, at least for humans, and primates. I imagine if there’s a correlation to group size and brain growth, that might be more a measure of social in-group stress and adaptation than out-group, but there are sure to be relations between the two as well. Personally, I think it’s the social, in-group conflict that is the more complex and also unrelenting, and so probably that that drove cranial growth. All critters have trouble externally, enemies and/or predators. This sort of smarts seems to be for dealing with each other.

    I also have a theory that we ramp up our social stress in order to make us better able and willing to fight the competing groups, antisocialization theory, or AST for short, so there’s a feedback sort of thing that would help explain what may have been some very rapid growth at some points in our prehistory.


    enjoying this site!

    1. Adam Benton says:

      Part of the issue is often you don’t have control over your territory size. Resource density varies across environments, and with it the size of territory you need to sustain your population.

      1. Jeff/neighsayer says:

        yeah, still though. You sure about the logic? I mean aren’t the firmest borders now the most contested ones? Until 911, we Canucks didn’t need a passport to go to the USA, loose border, friendly relations.

      2. Jeff/neighsayer says:

        and Greuter isn’t coming back to talk, is he? Maybe you can check my reply to them?

        1. Adam Benton says:

          It was 2 years ago. They’ll have gotten an email about your comment. Are they still at that address? Do they still care? These are all confounding factors though.

        2. Jeff/neighsayer says:

          Hey, it was over my head, but somebody tweeted some huge paper, all about pelvises and pelvic shape and evolution yesterday. I’m afraid I can’t recall a single detail, but again, I guess you know all about it. Maybe if you see it, you can find the sense in it for us both. I imagine it either clarifies this mystery I referenced, or it explains it . . .

        3. Adam Benton says:

          Do you have the title of the article?

      3. Jeff/neighsayer says:

        had to go back through Brian Boutwell’s Twitter feed. Here it is – http://onlinelibrary.wiley.com/doi/10.1002/ar.23542/epdf

        1. Adam Benton says:

          It’s essentially claiming that there’s more variation in the human pelvis than would be expected for a conserved trait. Aka a trait so vital for survival it can’t change too much without being fatal. This is interesting because it was thought to be a conserved trait, given how vital the pelvis is for walking and childbirth.

        2. Jeff/neighsayer says:

          damn. A wide open sort of question still, huh. Well it was always going to be maximally difficult figuring stuff out from a few bones . . . good thing there’s still plenty to learn, I guess. Thanks for deciphering it for me.

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