A Philosopher Takes on Evolutionary Psychology


“Evolutionary psychological inferences commonly fail to satisfy reasonable epistemic criteria.” The failures are so significant that good evolutionary psychology may not be possible. 

So argues Subrena Smith, a philosopher at the University of New Hampshire. Her paper, “Is Evolutionary Psychology Possible?“, was recently published in Biological TheoryIn it, she argues that the popular research program of evolutionary psychology is methodologically unsound.

Dr. Smith also wrote a shorter version of the argument that was published at The Evolution Institute. In it, she first presents a description of the aims of evolutionary psychology:

The mandate of evolutionary psychology is to give true evolutionary explanations for contemporary human behavior. Evolutionary psychologists believe that many of our behaviors in the present are caused by psychological mechanisms that operate today as they did in the past. Each mechanism was selected for its specific fitness-enhancing effects, and each of them is responsive only to the kinds of inputs for which it is an adaptation.

To achieve the aims of evolutionary psychology, researchers “need to show that particular kinds of behavior are underwritten by particular mechanisms.” More specifically, evolutionary psychology confronts what Dr. Smith calls “the matching problem”:

For a present-day psychological trait to be related to an ancestral psychological trait in the way that evolutionary psychology requires, the present-day trait must be of the same kind as the ancestral one. It must also have the same function as the ancestral one and must be descended from that ancestral trait as part of a reproductive lineage extending back to prehistory. Also, importantly, the present-day trait and the ancestral trait must be of the same kind and have the same function because the former is descended from the latter. This is key because it might be that a present-day trait and an ancestral trait are of the same kind and have the same function without one being descended from the other. The architecture of the modern mind might resemble that of early humans without this architecture having being selected for and genetically transmitted through the generations. Evolutionary psychological claims, therefore, fail unless practitioners can show that mental structures underpinning present-day behaviors are structures that evolved in prehistory for the performance of adaptive tasks that it is still their function to perform. This is the matching problem.   

For the matching problem to be overcome, three conditions must be met:

First, determine that the function of some contemporary mechanism is the one that an ancestral mechanism was selected for performing. Next, determine that the contemporary mechanism has the same function as the ancestral one because of its being descended from the ancestral mechanism. Finally, determine which ancestral mechanisms are related to which contemporary ones in this way. 

We can’t just assume that the identities required in these conditions are met. “They need to be demonstrated.” More specifically:

Solving the matching problem requires knowing about the psychological architecture of our prehistoric ancestors. But it is difficult to see how this knowledge can possibly be acquired. We do not, and very probably cannot, know much about the prehistoric human mind.

Some evolutionary psychologists dispute this. They argue that although we do not have access to these individuals’ minds, we can “read off” ancestral mechanisms from the adaptive challenges that they faced. For example, because predator-evasion was an adaptive challenge, natural selection must have installed a predator-evasion mechanism.

This inferential strategy works only if all mental structures are adaptations, if adaptationist explanations are difficult to come by, and if adaptations are easily characterized. There is no reason to assume that all mental structures are adaptations, just as there is no reason to assume that all traits are adaptations. We also know that adaptationist hypotheses are easy to come by. And finally, there is the problem of how to characterize traits. Any adaptive problem characterized in a coarse-grained way (for example, “predator evasion”) can equally be characterized as an aggregate of finer-grained problems. And these can, in turn, be characterized as an aggregate for even finer-grained problems. This introduces indeterminacy and arbitrariness into how adaptive challenges are to be characterized, and therefore, what mental structures are hypothesized to be responses to those challenges. This difficulty raises an additional obstacle for resolving the matching problem. If there is no fact of the matter about how psychological mechanisms are to be individuated, then there is no fact of the matter about how they are to be matched.

That is not the end of the problems, though. Dr. Smith says, “Even if these obstacles could be surmounted, the problem remains of identifying these behaviors with particular kinds of behavior that are hypothesized to have existed in prehistory,” and she goes on to explain the difficulties this further task faces.

You can read Dr. Smith’s full paper here and her summary of its argument here.

Over email, I asked Dr. Smith what the reaction to her argument has been amongst the evolutionary psychology crowd and she reported that there hasn’t been much of one, apart from some dismissiveness.

Discussion welcome, especially from those who work in psychology, biology, and philosophy of science.

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