In defense of evolutionary psychology, part 2: adaptationism and the reason human brains are so big

So in the first post of this series, I quoted the editors of The Adapted Mind as saying in effect that we can assume complex features of the human mind are evolutionary adaptations. And I know this is going to get them accused by some people of “adaptationism,” which is the alleged vice of assuming things are evolutionary adaptations despite of not having any good evidence that this assumption.

Sometimes these criticisms take the form of saying “in order to establish that something is an adaptation you have to do X, and you haven’t done X therefore your claim isn’t good science.” And I’m going to be frank, I think some people set the bar way too high for showing that something is an adaptation, and if your theory of science says that we can’t know whether or not certain things are adaptations so much the worse for your theory of science. In that case it’s your theory of science that’s flawed, not evolutionary psychology.

I think Steven Pinker nailed this one in How the Mind Works:

One claim is that reverse-engineering, the attempt to discover the functions of organs (which I am arguing should be done to the human mind), is a symptom of a disease called “adaptationism.” Apparently if you believe that any aspect of an organism has a function, you absolutely must believe that every aspect has a function, that monkeys are brown to hide amongst the coconuts. The geneticist Richard Lewontin, for example, has defined adaptationism as “that approach to evolutionary studies which assumes without further proof that all aspects of the morphology, physiology and behavior of organisms are adaptive optimal solutions to problems.” Needless to say, there is no such madman. A sane person can believe that a complex organ is an adaptation, that is, a product of natural selection, while also believing that features of an organism that are not complex organs are a product of drift or a by-product of some other adaptation. Everyone acknowledges that the redness of blood was not selected for itself but is a by-product of selection for a molecule that carries oxygen, which just happens to be red. That does not imply that the ability of the eye to see could easily be a by-product of selection for something else (pp. 165-166).

To give an example of this, let’s talk about human brain size. Human brains are very large relative to their bodies. Some animals like whales may have larger brains, but if you graph animal brain size against body size for many different animals, humans are very clearly an outlier. Why is this? Could it be a byproduct of something else rather than an adaptation?

Well, no. The problem is that evolutionarily speaking human brains are really expensive. First of all, it’s hard to get a head that big through the birth canal, even when you’re talking about a baby’s head which is smaller than an adult human’s head. Those big heads we have are the reason that women dying in childbirth used to be such a big problem before the coming of modern medicine. Also, brains are expensive in terms of metabolic energy. They’re a tiny fraction of our total body mass, but they use something like 20% of our daily energy intake.

If human brains were just an unfortunate side effect of something else going on in human evolution, two things would have to be true. First of all, whatever was driving that other thing would have to be so powerful as to be able to overcome the strong selection against big brains for reasons of death in childbirth and the energy cost.

Second, it would have to be true that spite of the big selection pressure, evolution would have to turn out to be unable to decouple brain size from whatever that other thing was. And that seems extraordinarily improbable. That gives us pretty good reason to think that there must be a big evolutionary benefit to having large brains, large enough to outweigh the costs. Even if we don’t know what that benefit is.

The situation with language is similar, though not because being able to speak a language is so costly, but just because the ability to speak a language is clearly a complex feature of the human mind. Linguists have realized since about the time of Noam Chomsky in the 50s that if we learned language through a totally general-purpose learning mechanism, we would never learn languages fast as we do.

If you look at how toddlers learn language, they don’t learn it through simple induction. The only real way to explain why we would have these language learning mechanisms is that the ability to learn language gave us some kind of benefit in our evolutionary past. (I won’t go any further into the details of language here, but if you’re interested in that subject, I recommend another book by Stephen Pinker, The Language Instinct.)

Now I don’t claim to know for sure what exactly was the main driving force in the evolution of language and the evolution of human intelligence more generally. Was it that these things made us better hunter-gatherers? Did they evolve to help us better plot against rivals? Did they evolve to help us impress members of the opposite sex, as Geoffrey Miller proposes in his book The Mating Mind?

I’m not sure. I suspect it was a combination of all these things, but I don’t really know. But that doesn’t stop me from being very confident that they are adaptations for something, and we shouldn’t be so cautious about seeing traits as adaptations as to stop ourselves from saying that. And the difficulties here shouldn’t stop scientists from at least trying to make educated guesses about what drove the evolution of human intelligence.

Note: edited for paragraph breaks.

  • Reginald Selkirk

    And I’m going to be frank, I think some people set the bar way too high for showing that something is an adaptation, and if your theory of science says that we can’t know whether or not certain things are adaptations so much the worse for your theory of science. In that case it’s your theory of science that’s flawed, not evolutionary psychology.

    Then I’ll be frank with you: scientists are not going to take well to such a high-handed pronouncement coming from a non-scientist such as yourself.

  • Reginald Selkirk

    Now I don’t claim to know for sure what exactly was the main driving force in the evolution of language and the evolution of human intelligence more generally… And the difficulties here shouldn’t stop scientists from at least trying to make educated guesses about what drove the evolution of human intelligence.

    You named a few possible selection pressures; with a little more digging you could probably find at least a dozen. And nothing you have said should stop scientists from pointing out that those “educated guesses” are lacking in scientific rigour.

  • scenario

    I always thought the what if story as the first step in the scientific process. Start with what if, then formalize it, figure out how to test it, then test it. If it consistently passes the tests, its a theory.

    The only problem with what if stories is when people stop there and pretend it’s science.

  • http://www.facebook.com/chris.hallquist Chris Hallquist

    Reginald, I’m talking about ideas that have been proposed and discussed at some length by scientists. The real problem is when those scientists’ ideas are dismissed out of hand on philosophical grounds. Do you deny we have good reason to think that large brains and language are adaptations?

    • Reginald Selkirk

      Do you deny we have good reason to think that large brains and language are adaptations?

      No.
      .
      And there’s nothing wrong with the next step either, “trying to make educated guesses.”
      .
      The problem happens when someone gets fixated on their “educated guess” and proclaims it to be the actual solution, despite not having put in a rigorous scientific treatment; or even noting that a rigorous treatment may not even be possible. The problem is compounded when the mainstream media trumpets this as the latest scientific finding without communicating the relative weakness of the argument.
      .
      In short, the problem is the same reason why participants of the more rigorous sciences put “social sciences” in scare quotes.

  • jg29a

    And I’m going to be frank, I think some people set the bar way too high for showing that something is an adaptation, and if your theory of science says that we can’t know whether or not certain things are adaptations so much the worse for your theory of science.

    And I’m going to be even franker: many such people (including many scientists) set such a bar very selectively and not accidentally, but do so rather in order to defend certain cherished assumptions coming out of the humanities, which are generally built upon anecdote in ignorance of both evolutionary principles and statistical analysis.

    scenario:

    The first is precisely what evolutionary psychologists do. Some prominent models are strongly supported by large amounts of converging evidence, such as gender differences in mating preferences and attractive judgments being understood in terms of different ancestral reproductive challenges and strategies. Other hypotheses are weakly supported if at all, such as men having an innate advantage at spatial reasoning because men were hunters, or some such. Like any academic field, there is a continuum from very well-grounded to highly conjectural views out there in the meme pool, and, also like any academic field, researchers often want to explore the ideas in the middle of that continuum rather than hammer away at the already well-supported claims.

    This very same pattern is evident in my own field of linguistics and language acquisition. The main difference is that when we explore our plausible but less-than-perfect explanations, we don’t have a ton of ideologues out of the humanities brazenly mischaracterizing our claims, slandering us as “rape apologists” or “Republicans” (hehe), and regularly propping up fringe popularizers like name-already-mentioned-far-too often-Japanese-bigot-guy while ignoring the current leaders in the field like Cosmides and Tooby, Buss, Kurzban and, yes, Daniel Dennett.

    No, I’m not a biologist, but my position – apparently shared by those linguists who are doing most to push the field forward – is that linguistics cannot be done well in this day and age without psychology or evolutionary theory, those two going hand-in-hand. I honestly have no clue where to draw this magic line in human cognition or learning where some behavior or feature is supposed to be too “social” for evolutionary principles to be applied. The more I read in EP and its critics, the more I find it to be a vague, slippery and unnecessary partition.

  • Reginald Selkirk

    So here’s another class of “science” that causes participants in the more rigorous sciences to roll their eyes: diet and health studies.
    White rice link seen with Type 2 diabetes, says study

    “What we’ve found is white rice is likely to increase the risk of Type 2 diabetes, especially at high consumption levels such as in Asian populations,” Qi Sun of the Harvard School of Public Health told AFP.

    Note that, according to this quote (and I cannot vouch for its accuracy), the researcher is clearly stating a causal link, whereas it is almost certain that the study involved did not establish causality, but only correlation. Much further down, we get to the disclaimers:

    Sun said the study did have limitations, including full details about what the volunteers ate in addition to rice.
    “I don’t think I can put forward a 100-percent confirmed case, given that this is a meta-analysis of four original studies,” he said.
    “But I see a consistency across these studies, and there is biological plausibility that supports the association between white rice consumption and diabetes.”

    A meta-analysis! Don’t get me started.
    And here we see the admission that the result is only a correlation, which clearly contradicts the more positive statement found earlier in the article.
    .
    .
    Can you see how reports of this kind of “science” might cause physicists who deal with experimental verifications accurate to tens of decimal places, or biologists who know that the theory of evolution has been consistently and repeatedly confirmed for 150 years, to chafe a bit; and to worry that the “science” brand is being diluted, which will play to the hand of the “only a theory” crowd?
    .
    And the “educated guesses” you talk about for evo psych are even less rigorous than the above-referenced diet and health study.

  • Reginald Selkirk

    Rigorous science:
    Research group reports result that neutrinos are faster than light, backed up by an experimental result measuring a 60 nanosecond anomaly.
    Reaction from researchers in relevant fields is that the result is probably wrong.
    Reputable astrophysicist notes that the result violates decades of previous observations, including astronomical events.
    Nobel laureate writes paper on theoretically predicted effects which we could expect to observe if the result were true, none of which are observed.
    Careful inspection of the equipment used for the original experiment turns up a loose cable in a key piece of equipment.
    Another research group replicates the experiment, and comes up with a negative result.
    .
    .
    What happens in a typical example of evolutionary psychology:
    Archaeologist with no particular expertise in genetics, and who has never heard of R.A. Fisher or W.D. Hamilton, has a brain fart and comes up with an “educated guess” about why humans developed big brains.
    The mass media articles all being “Scientist says…”
    .
    Psychologist with no particular expertise in genetics has a brain fart and comes up with a different “educated guess” as to why humans developed big brains.
    More mass media articles about the latest findings of “science.”

  • http://www.facebook.com/chris.hallquist Chris Hallquist

    Does this describe the work of any of the people I listed above?

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  • http://www.modernpsychologist.ca Brad Peters

    Chris, I think you are making several assumptions before you even begin defending EP. I believe we need to start with the theoretical assumptions of the field – in short: HOW THEY DEFINE THE MIND. I am a psychology professor interested in theoretical psychology and I have severe reservations about EP as a field. Not only do I believe it to be a bad theory for human behavior, but I also think it could even be downright dangerous if its ‘evidence’ is permitted to influence social policy.

    You can read my own critique of evolutionary psychology and a follow-up discussion where I write more candidly about evolutionary psychology and theoretical faith. If you read the comments in each, you might get a sense as to what I am talking about. I agree, critics are often cited as ‘misunderstanding’ the field – but it would seem that a requisite for ‘understanding’ involves endorsing it. If you have not read anything by Popper or Kuhn, I would suggest doing so, if only to get an appreciation for how theoretical camps can become so entrenched and how the ‘science’ is often based on assumptions – ones that we tend not to question. Many of the philosophically-minded critics are aware of this fact, while EP brushes it off while re-affirming its ‘evidence.’ For this reason, the field has also been accused of scientism. We should not forget that good science is a mix of both empiricism AND sound reasoning.

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