Did finding food drive our brain’s evolution?

It’s another week, which means it’s time for another theory about how humans evolved such big brains. Last week a scientist argued inter-group conflict was responsible. Now an EvoAnthist from California is claiming that primate intelligence evolved to help us extract and process food1. Why all the different ideas? Are scientists baffled? Hardly. In the past few years it’s become increasingly apparent that there’s no single explanation for our big brains. Instead, a lot of factors were driving their evolution. Focused has now shifted towards trying to identify which of those factors was the most important.

Currently, it looks like sociality was the dominant evolutionary force responsible for our big brains. The social brain hypothesis posits that larger brains helped us have stronger relationships with more people. In turn, this allowed us to live in larger groups; which could search a wider area for food, better defend that territory against competition and so on2.

Now don’t worry. I’m not just trying to pad out this post with a discussion of other ideas. The social brain hypothesis is directly relevant to the new research. This is because of how it established itself as the “dominant” force in primate evolution. Dunbar – author of the social brain hypothesis – did this by comparing the correlation between brain size and group size in primates and noting how it was stronger than the link between brain size and other factors. For example, some had argued that large brains might have evolved to help primates remember when and where fruit ripened. However Dunbar showed that the link between amount of fruit consumed and brain size was weak; challenging this hypothesis2.

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

Dunbar’s comparison of brain size and many different factors. Bottom right is the correlation between group size and brain size, which is the strongest. Thus suggesting sociality was the most important factor examined. No, I have no idea why he put monkeys all over his favourite graph.

Now, the observant amongst you might have noticed the bottom left graph. This compares the complexity of the tools and techniques primates use to extract food from the environment (known as “extractive foraging”) with their brain size. Stuff like chimps using spears to extract meat from monkeys. Crucially, it notes that the correlation between the two is relatively weak; suggesting it was not an important factor in the evolution of primate brains.

This is what the latest research challenges.

It starts with a rather scathing critique of Dunbar’s work, arguing he used an overly simplistic model of extractive foraging. Whilst his contains three “levels” of it, other primatologists have developed a scale twice as large; containing many more sub-categories. This would be a much more representative view of how complex the extractive foraging techniques of these species are. The study also criticises the primate species Dunbar used in his study; noting that several that would score highly on that scale which were omitted. Like orang-utans1.

So you can probably see where this is going right? Having found a better metric for extractive foraging and a larger data set to examine; the research repeats Dunbar’s experiment and discovers there is a correlation between brain size and extractive foraging after all.

Haha, no. That would be too logical. Instead, after having poopooed Dunbar’s work the paper…kinda…just…ends…

My reaction when I realised what was missing from this paper

My reaction when I realised what was missing from this paper

The closest it comes to making a positive link between brain size and extractive foraging is a reference to a paper from 2011. This other research tried to come up with a sort of “primate IQ” by looking at 7 or so “smart” things primates do that were correlated with other smart behaviours. The total set of these things was, in turn, correlated with brain size. Extractive foraging made the cut, but group size didn’t (although the study did note they found a link between brain size and group size anyway)3.

In other words, this research doesn’t make a particularly strong case that using complex tools and techniques to extract food from the environment was an important factor in the evolution of our big brains. Sure, it does a very good job of establishing that the extractive foraging hypothesis isn’t wrong. And that is kind of important. The idea has been sidelined since Dunbar’s criticism; maybe now it will be discovered to be important after all.

However, there’s a fairly big gap between “isn’t wrong” and “right.” This research fails to make that leap.

References (check out the dates, I’m bringing you research from the future!)

  1. Parker, S. T. (2015). Re-evaluating the extractive foraging hypothesis. New Ideas in Psychology, 37, 1-12.
  2. Dunbar, R. I. (1998). The social brain hypothesis. brain, 9(10), 178-190.
  3. Reader, S. M., Hager, Y., & Laland, K. N. (2011). The evolution of primate general and cultural intelligence. Philosophical Transactions of the Royal Society B: Biological Sciences, 366(1567), 1017-1027.

5 thoughts on “Did finding food drive our brain’s evolution?

  1. Maybe this is incredibly ignorant, but is there any possibility the cart is in front of the horse? Rather than various social or environmental aspects driving brain size, could brain size have come first and in turn allowed the social progress?

    It would be silly to posit some large black monolith, but could there be an evolutionary accident of some kind that “jump-started” brains and all the rest just followed?

  2. The gap between “isn’t wrong” and “right” is important for Dunbar’s work as well as the ripostes. The sociality hypothesis is put across as an explanation for a (supposedly) neat correlation between bonding opportunities and conflicting ecological demands [e.g. 1,2], and elsewhere Dunbar has claimed that human language is partly responsible for driving larger group and brain sizes in Homo sapiens because it is better for large group cohesion than grooming [3]. Some of this seems compelling in the abstract, although some of the maths used for relating early hominid cranial volumes to potential group sizes seems ambitious, but in my opinion, the argument suffers from two main problems:

    The first is that your framework for understanding sociality, bonding, and group size has to be restricted to primates because the correlations rapidly break down when looking at other kinds of animals. One might argue that there’s reason to believe primates have a particular constraining biological endowment that causes this correlative effect, but one might also argue that we’re looking at long-standing cultural endowments and are confusing the two. The other problem is that the argument makes strong predictions about the (non-)viability of large groups of a certain number among primate species and there does seem to be some counter-evidence for those limits [e.g. 4].

    It seems fair enough to claim some kind of connection between these varied observations but going after an explanation often leads us to bickering over chicken-and-egg directionality. Forced to choose, I would say that many of the features Dunbar identifies as the causes of human sociality and brain size evolution are actually either consequences or spandrels but, in reality, I think we need to be thinking more about feedback loops, i.e. sociality drives brain size drives sociality and so on. Here’s an article on that subject which stuck in my mind recently: http://aeon.co/magazine/science/why-the-symbol-of-life-is-a-loop-not-a-helix/

    1. Dunbar, R. I. M and S. Schultz (2007), ‘Understanding Primate Brain Evolution’, Philosophical Transactions of the Royal Society B 362, 649-658.

    2. Lehmann, J., A. H. Korstjens and R. I. M. Dunbar (2007), ‘Group size, grooming and social cohesion in primates’, Animal Behaviour 74:6, 1617-1629.

    3. Dunbar, R. I. M, ‘Why Only Humans Have Language’ (2014) in ‘Lucy to Language: the Benchmark Papers’, eds. R. I. M. Dunar, Clive Gamble & J. A. J. Gowlett (Oxford, OUP), pp. 427-445.

    4. Thurston C. Hicks et. al. (2014), ‘Absence of Evidence is not Evidence of Absence: discovery of a large, continuous population of Pan troglodytes schweinfurthii in the Central Uele region of northern DRC’, Biological Conservation 171, 107-113.

  3. It is very interesting that the discussion re the development of sapiens “abnormal sized” brain keeps
    reoccurring. Of course, this peculiar object being so interested in itself is not a new phenomena.

    It does seem as though, in terms of evolution, one should stick to the basic rules. Functionality
    in terms of survival of a species being the base line? When considering the brain, one should take
    cognizance of the fact that it obviously has more than one primary capability such as memory or its
    cognitive abilities. It for example regulates your sense of balance.

    Besides this Sapiens has an imagination, creativity, and I think one could say, abstraction, as abilities
    as well. Question is:- What in the forces of evolution generated these abilities? The evolution of the
    basic functions of the brain one can easily understand as being driven by a multitude of ecological
    factors and mutations to the point of development Erectus apparently achieved.

    As a student I read a study that concluded that specific ecological conditions would determine ideal
    group sizes for hunter gatherers. I think that figure came down to 27 clan members all in all.It also
    read that Sapiens would need the ability to trot specific distances per day to maintain a viable
    protein intake daily. As I remember, that came down to 11 km per day on average.The mechanism
    of our feet were evolved to comply. I think these studies were done by studying the San in there
    natural habitat. With this in mind it, is logical that a specific brain capacity would be a necessity.

    The real question is;- What caused our brains to do what they are capable of today. If one just
    attends to how art developed over time, you must be in aw. Fact is, there does not seem to be
    an end to this process in some societies. I wish I had the ability to comment on the development
    of maths over the last 500 years. I cannot see or understand any “natural” factors that could have
    resulted in the brain development some Homo Sapiens display in the process of evolution as we
    understand it today.

    There could be one possibility I have heard of, but not read on as yet. That is the possibility that
    Homo sapiens has acquired the ability to transfer info almost directly from parent to offspring. We
    know that if “stupid” earthworms are fed “clever” earthworms the “stupid” ones become better
    problem solvers. if a factor, like this example interceded, one could reason that evolution does
    not explain every development and then we could have a really huge problem. Maybe someone
    knowledgeable knows?

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