Field of Science

On evolutionary psychology: foundation

At some point a scientific theory may become so well established, having withstood test after test, that it can then be used for useful predictions. Electromagnetism and general relativity comes to mind. These theories are being used every day for prediction, in scientific research as well as for more practical purposes.

Biology has mostly been devoid of theories of this caliber, and this is mainly due to the complexity of life. And by complexity I here mean that it is very complicated to understand, because there are so many more parameters to account for compared to electromagnetism etc. The theory of evolution, mathematically the most advanced in biology, has also been tested relentlessly, and, while a theory in flux, has come up on top every time. Additionally, some parts of the theory can be used to predict outcomes with high precision, namely in the case of population genetics, which predicts allele frequencies in population under the four forces of evolution: natural selection, mutation, genetic drift, and gene flow.

But the part of the theory which is historical, i.e. where it attempts to deduce what happened in the past, isn't quite as rigid. This is not a special feature of the theory of evolution, really, but just a general problem inferring about past events. Physics is on comparably shaky ground when it is used to tell us about the history of the Universe, for example. Phylogenetics, the discipline of reconstructing evolutionary relationships among species (or larger groups of species, or of genes), based on the idea of common ancestry of species, have had many successes "predicting" past events. Hypotheses can actually be tested, given the fossil record and the extensive genetic data we now posses.

Evolutionary psychology, on the other hand, is quite another story. It is a discipline in psychology (and not in biology) that attempts to make sense of the human psyche in the light of evolution. Specifically, human traits, such as behavior and instincts, are given explanations that make sense in the light of natural selection. EP relies heavily, to the point of exclusion, on natural selection (including sexual selection) to understand why we are as we are. In fact, the Tooby and Cosmides 2005 paper on the foundations of evolutionary psychology begins by recognizing that it is the "theory of evolution by natural selection [that] has revolutionary implications for understanding the design of the human mind and brain," not the theory of evolution. At this point we notice that this means only one of the four forces of evolution is invoked. Notably, genetic drift is completely ignored, as it is an effect of random sampling, which does not offer sexy explanations of human traits. "The fact that humans are instinctively afraid of snakes evolved via genetic drift, and as such is a trait that doesn't really mean anything in our evolutionary past or present." That doesn't really make any sense in the case of ohidiophobia, but even if it did it wouldn't be something that would be worth the effort for an evolutionary psychologist to report to the rest of the scientific community, nor, and this becomes important*, to the general public.

The reason I started out by talking about the theory of evolution as an established theory was to drive home the point that we now do know, as much as it is possible to know anything about the past if you weren't there in person, that natural selection has been a major component in shaping life as it evolved, and that undoubtedly includes the human psyche. However, that does not mean that we can know for certain what the adaptive value of a given trait was when it evolved (here I really mean "went to fixation because of" when I say "evolved"). Take the female affinity to the color pink. Women like pink more than men do. This is something that can be easily confirmed by experiments with real live humans. Once the fact is substantiated in this way, evolutionary psychologists proceed to invoke the natural selection to explain it. "Women like pink because our female ancestors had to be more sensitive to that color when they were gathering fruit, and had to pick the best ones." This might be a decent hypothesis, but it is one that cannot be tested. If it cannot be tested, it is a dead end, scientifically speaking. If we could rule out all other hypotheses, then we would have a strong case, but we humans are very good at coming up with stories to explain the world around us. "Women like pink because the were the ones raising babies and thus needed to be highly attuned to the color of baby cheeks (which are pink on occasion)."

Moreover, just because a trait has a specific function at the present doesn't mean that it initially evolved by selection acting on that trait. The trait could have had a different function, which then changed as the environment (or rather, the fitness landscape) changed. One example is feathers, which without a doubt is functional in flying, but most likely first evolved as insulation. Such co-option, or exaptation, is very common in evolution. Yet, selection is all evolutionary psychologists have to work with, and they apply it heavily to tell some very intriguing stories* about the evolution of the human mind.

*Which is the subject of another post coming soon.


  1. A correspondent of mine is an evolutionary psychology PhD candidate, and truly a paragon as far as I'm concerned in the field - since he and I wrote (me questions, him citations to books and answers) extensively on the topic, I'm afraid I might have to slightly disagree with you, here. It is possible to make EP predictions based on the assumption that evolved traits would be prevalent within the human species regardless of cultural background. That said, if you find, say, Papua New Guinean females who are instinctively more attracted to pink than are male PNG's (supposing you could reasonably make such experiments without bias) - then you would, in principle, be supplying EP evidence that women are more into pink. You're, though, that saying WHY they are more into pink is a problem. I suppose you can predict based on what you know about pink that this or that of a female trait has more of a selective value if females are more sensitive to pink.

    Personally, I think pinkness is just a fad, but who knows. I still think it's a falsifiable prediction, at least on principle - it's just very hard to create the tests that could attempt to falsify it.

  2. That said, if you find, say, Papua New Guinean females who are instinctively more attracted to pink than are male PNG's (supposing you could reasonably make such experiments without bias) - then you would, in principle, be supplying EP evidence that women are more into pink. You're [right], though, that saying WHY they are more into pink is a problem.

    This is exactly the difference between psychology and evolution. The first part has nothing to with evolution, and you can test it. The "why" question is where evolution enters, together with a lot of assumptions.

  3. Um, why can't psychology have "why's"?

  4. There are of course "why's," but in answering them EP turns to evolutionary theory.

    You can make experiments of human traits, e.g. the difference in color preference between men and women. Once you have established that there is a difference, you ask why that is. Answering that question EP looks at our evolutionary past for an answer. It's what makes the most sense in many cases, but that does not mean that it is enough to just say "it makes sense that women like pink, because...." That hypothesis would have to be tested, and no one in EP ever does that.

  5. I don't follow you. Isn't "turning to evolutionary theory" for psychological answers what EP is all about? It uses ToE to predict (or retrodict, or whatever) what we can find in human nature. I can even imagine clinical application of such predictions. So where did the "whys" go?

    Like I said: the "pink preference" can be tested if you isolate cultural influences and posit an evolutionary imperative for preferring pink. That would make the "evolutionary" side of the deal happy. Of course, like a lot of evolutionary explanations, it would have a "just-so tale" flavor - but that's what you get when you try to predict things based on very ancient history. You have to ignore a lot of facts that are simply unknowable.

  6. The testing of the pink preference has nothing to do with evolution. It's all psychology. When the psychologists then ask the why-question, then they turn to evolution. But at that point there is no further testing.

    I can even imagine clinical application of such predictions.

    If one could use the evolutionary explanation of pink-preference to predict something else about human behavior/psychology, then you would have a strong case for the hypothetical pink-preference explanation. That would be awesome indeed. I have just never seen any such study.

  7. The only book I've read which really tries to predict EP predictions is "Rape: a natural history of sexual coercion" by Palmer (and another guy I can't remember the name of). EP is a very new science, but it is, however, a science, in my opinion.

    I'm sorry, I've read your reply again and again and I can't help but thinking that either I'm just not smart enough to understand the separation between EP and psychology here. The testing itself is the answers the psychologists get *based* on evolutionary thinking. This is definitely where the testing starts, but I wouldn't say it's where it ends!

    BTW, in Rape, Palmer&co predicted that based on evolutionary theory, women who are specifically of reproductive age and even women who are ovulating at the time of their sexual coercion are most likely to be most traumatized and badly affected or even (!) to be actually raped. This stands in stark contrast to the fact that it's much easier for sexual predators to prey on younger adolescents or even prepubescents and even older women (who are, while not as "attractive" as their young counterparts, are much easier to subdue).

    This is something they predicted *before* getting into the evidence.

  8. Sorry. I realize what I write is a little muddled.

    Forget for a moment that EP is anything but psychology. It's just psychology. Nothing about our past. They do an experiment and find that women prefer pink. That's it. They ask why that might be, but are unable to find any plausible answer until they turn to evolution.

    The pink-preference is then assumed to to be adaptive, and a hypothesis is given to explain why pink-preference would be adaptive.

    THEN END. But, as in your rape example, this hypothesis might be used to predict other data, and that would indeed validate the hypothesis. It's just that most often evolutionary psychologists don't do this at all. In that case it becomes a lot of just-so story telling.

  9. Now you hit the mark. Just-so story-telling is a problem in evolutionary theory in general precisely because of our mostly obscure and ancient past. You CAN make certain predictions, but there's a much wider restriction on how far you can go.

    On the other hand, EP allows for something quite extraordinary to psychology, and that is the wonderful addition biology adds to any scientific field that deals with humans: the ability to compare to other animals and species. Such comparisons would be completely meaningless except within an evolutionary construct.

  10. Quite. EP does the only thing that seems possible, namely to explain our psyche by looking at our evolutionary past (save for creationist explanations of the human mind: "God intended it that way"). Just often done in a very sloppy way, leaving it at just-so stories.


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