The field of evolutionary psychology (“evo psych”) claims that virtually all of human behavior can be explained by past selection pressures shaping our brains. This means that not only did everything below your neck evolve, but so did everything above it. That includes not just base behaviors like your desire to eat an orange or cuddle with your significant other, but even your higher activities, like appreciating music, creating art, and worshipping God. If evo psych’s insights are correct, then all of your higher behaviors are no more than the result of selection on your Pleistocene hominid ancestors.

Swinging from the Abstract

If that sounds a little far-fetched, you’ll find some agreement from a new paper in the journal Biological Theory. Philosopher Subrena E. Smith at the University of New Hampshire asks, “Is Evolutionary Psychology Possible?”  Smith comes out swinging from the abstract: 

In this article I argue that evolutionary psychological strategies for making inferences about present-day human psychology are methodologically unsound. Evolutionary psychology is committed to the view that the mind has an architecture that has been conserved since the Pleistocene, and that our psychology can be fruitfully understood in terms of the original, fitness-enhancing functions of these conserved psychological mechanisms. But for evolutionary psychological explanations to succeed, practitioners must be able to show that contemporary cognitive mechanisms correspond to those that were selected for in the environment of evolutionary adaptedness, that these present-day cognitive mechanisms are descended from the corresponding ancestral mechanisms, and that they have retained the functions of the ancestral mechanisms from which they are descended. I refer to the problem of demonstrating that these conditions obtain as “the matching problem,” argue that evolutionary psychology does not have the resources to address it, and conclude that evolutionary psychology, as it is currently understood, is therefore impossible.

In an interview with Gizmodo, “This Philosopher Is Challenging All of Evolutionary Psychology,” Smith further boils the problem down:

The matching problem is really the core issue that evolutionary psychologists have to show that they can meet: that there is really a match between our modules and the modules of the prehistoric ancestors; that they’re working the same way then as now; and that these modules are working the same way because they are descended from the same functional lineage or causal lineage. But I don’t see any way that these charges can be answered.

Her argument is well reasoned and compelling. She says we simply lack the data to establish the veracity of many evo psych claims. 

How About Some Standards?

She argues that proponents of evo psych ought to be held to basic standards of evidence. For example:

Evolutionary psychologists argue that behaviors in the present are caused by cognitive systems that operate today as they did in the past. In their view, each module was selected for because of its specific fitness-enhancing effects in the EEA [environment of evolutionary adaptedness], and each of them is domain-specific — that is, responsive only to the kinds of inputs for which they are adaptations.

Evolutionary psychological inferences are secure only if it is possible to determine that particular kinds of behavior are underwritten by particular structures. Further, these must have the evolved function of producing behaviors of just these kinds.

If you claim that a particular modern behavior is caused by a particular psychological structure that arose due to particular selection pressures, then you need to show that a particular structure causes that behavior and that it was in fact selected to produce that behavior. Her argument is so reasonable, and so obvious, it’s a bit concerning that she needed to say this at all. Did evolutionary scientists not understand these things already?

Might Not Be Enough

Yet even meeting such basic standards might not be enough to demonstrate the claims of evo psych. As Smith continues:

If present-day human behaviors are caused by special-purpose cognitive structures, and that was also true of our stone age ancestors, and if there is a high degree of concordance between the structures populating the modern mind and those that populated the minds of our prehistoric ancestors, this would still fall short of securing evolutionary psychological inferences. This is because it might be the case that the similarities between prehistoric and modern cognitive architectures are due to ontogenetic processes — similar experiences producing similar functional differentiation in the brain. For a contemporary trait to be a strong vertical homolog of an ancestral trait, the contemporary 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 related by descent to that ancestral trait as part of a continuous reproductive lineage extending back to the EEA. Additionally, it must be the case that the contemporary trait and the ancestral trait are of the same kind and have the same function because the present-day trait is descended from the ancestral trait. In principle, 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. If this is the case, then the architecture of the minds of present-day humans would resemble that of early humans without it being the case that this architecture was selected for and genetically transmitted through the generations.

In other words, it’s not sufficient for evolutionary psychologists to speculate about the advantage that some modern-day behavior might have yielded in our Pleistocene ancestors in the environment that shaped our brains (what she calls the “EEA”). They need to demonstrate that the contemporary behavior would be similar to the ancient one, and that our ancestors had the same genetically related cognitive machinery producing their trait as we have producing ours. This sounds reasonable, too.

Necessarily Fruitless

Smith maintains that some evo psych explanations entail traits that were acquired too recently to be the product of natural selection. Thus, attempts to explain them in evo psych terms must be fruitless:

If the idea that mental structure can be acquired ontogenetically seems dubious, consider the area of the brain called “the visual word-form area” that is specialized for reading (it is a “reading module”). Written language emerged only around 3500 years ago, so it is too recent for reading to have been selected for. This shows that cognitive mechanisms can be acquired by learning. [Citations omitted.]

Evolutionary psychology cannot solve what she terms the “matching problem.” That means “evolutionary psychological claims fail unless practitioners can show that mental structures underpinning present-day behaviors are structures that evolved in the EEA for the performance of adaptive tasks that it is still their function to perform.” To solve the matching problem, as Smith explains in a blog post at The Evolution Institute, three criteria must be met:

Ancestral and present-day psychological structures have to match in the way that is needed for evolutionary psychological inferences to succeed. For this, 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.

It’s not sufficient to assume that the required identities are obvious. They need to be demonstrated. 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.

In its typical fashion, evo psych feels little need to meet these basic standards of proof. Why? Because “There seems to be a tacit assumption amongst evolutionary psychologists that the needed identities between contemporary psychological mechanisms and ancestral ones are so obvious that they do not need to be established.” Smith argues in her paper:

Unless the challenge can be overcome, evolutionary psychological explanations fail. Put more strongly, if the matching problem cannot be solved, evolutionary psychology is impossible.

She gives an example of an evo psych study about attitudes toward sexual fidelity. The research surveyed college students to purportedly show that males are more concerned about the fidelity of their female partner than females are about that of their male partner. Smith notes that such a study could never solve the matching problem:

Faced with evidence that 21st-century male American college students are more doubtful of the future sexual fidelity of their mates than their female counterparts are, the authors make two assumptions. The first is that male college students’ skepticism is caused by a hardwired, domain-specific cognitive module. The second is that this module existed in Pleistocene males, and produced behaviors of the same sort as the contemporary behavior. These assumptions are supposed to underwrite the conclusion that the sexual suspiciousness of contemporary males is caused by a cognitive mechanism with the evolutionary function of enhancing their fitness by preventing cuckoldry.

Goetz and Causey do not provide support for their claim that the psychological mechanism driving contemporary male sexual skepticism is a strong vertical homolog of the mechanism that drove (hypothesized) prehistoric anti-cuckoldry behavior. Consequently, their inferences about the evolutionary origin of the male students’ attitudes is unjustified. 

Give Them a Break

A skeptical reader might be thinking at this point, “Fine, but let’s give evo psych a break! Brains and behaviors don’t fossilize, so it isn’t fair to expect researchers to demonstrate the existence of ancient behaviors, much less to show that we have modules that existed in our ancestors.”Smith is ready for this objection. If the data aren’t available, that doesn’t give you the right to engage in data-free speculation: 

It might be thought that I am unfairly holding evolutionary psychology to a much higher epistemic and methodological standard than is normally used in evolutionary biology. But this is not the case. Evolutionary psychological inferences commonly fail to satisfy reasonable epistemic criteria. 

When making evolutionary inferences about paradigmatically biological traits, biologists use experimental manipulations, comparative methods, the fossil record, and optimality models to determine that selection has taken place and that the items under consideration have retained their selected-for functions.

Evolutionary psychologists are impeded by the fact that these methods are unavailable to them. … evolutionary psychological hypotheses turn on inferences about hypothetical cognitive structures — the mental modules — for which there is a dearth of empirical support … and there is no evidence that the minds of our prehistoric ancestors possessed this sort of cognitive architecture.

Circular Reasoning

Smith also charges that evo psych engages in “circular” reasoning when “individuating” behaviors. Individuating means identifying specific behaviors based upon their specific effects, functions, or causes. To individuate a behavior based on its effects, “one needs to establish that the contemporary and ancestral causes of the behavior (structures) are strong vertical homologs,” but she explains that evo psych has no mechanism for doing this. To individuate a behavior based on its function entails “circularity,” because it “illegitimately supposes that a behavior was selected for and then uses this supposition as evidence that the behavior was selected for.” To individuate a behavior based on its causes falls into the same trap, because “it relies on the principle that cognitive mechanisms are individuated by the behaviors that they bring about while these behaviors are individuated by the mechanisms that supposedly cause them.”

In light of these difficulties, Smith asks: “Is evolutionary psychology possible?” The answer is no. She concludes: “Evolutionary psychologists simply do not have the methodological resources to justify the claim that the psychological causes of contemporary behaviors are strong vertical homologs of the psychological causes of corresponding behaviors in the EEA.”

It’s remarkable and encouraging to see such clear thinking in a mainstream scientific journal. Even evolutionary biologist P. Z. Myers jumped on this bandwagon, writing about the field of evo psych, “None of their prior claims are valid, and they don’t fit with what we do know about evolution and the brain!” But will these criticisms have any effect on the field itself? Myers concludes that evo psych is too insular for that:

Not that any of this will have any effect on EP at all — that’s a field that relies more on an emotional belief that they can study the past entirely by imposing their desired conclusions on weak data. Smith, on the other hand, has a strong understanding of logic and recognizes where these Evolutionary Psychologists have made a huge leap beyond what the data entails.

Ideology and Consequences

At Gizmodo, however, Smith attributes the resistance to criticism among evo psych practitioners to their “ideological biases.” She warns of potential consequences of their unwillingness to listen:

The evolutionary psychologists I engage with are not silly people. They are thoughtful and philosophical about these matters. However, the attractiveness of evolutionary theory coupled with peoples’ ideological biases forces them to not be as careful as they might be otherwise. I think that the consequences for our world when we misappropriate evolutionary accounts are really serious. People are saying that people of color have smaller brains, which is not true, or that women aren’t as great as men, which is not true… I think we have a special responsibility, when we say evolution made us that way, to recognize that people will read “innate” or “hardwired” as synonymous with evolution. We should be especially careful to not be making claims like these, which can have consequences.

If you say evolution made us so, then governments can rightly say you don’t have the capacity to do something, so we won’t use our resources to make you do stuff you can’t do. This is about the science and politics — making sure that we’re not misappropriating the science to underwrite our politics in a way to suit interests, be they my interests or their interests. If I have interests inconsistent with what the science says, I don’t think I should be given a pass. But my view is that I don’t see the framework of evolutionary psychology as-is providing us with an explanation of human behavior that we can get behind.

Just to be clear: Smith is not anti-evolution. As she writes at The Evolution Institute, she believes “The human mind was fashioned by evolutionary forces in ways that allowed our ancestors to be successful.” But as for evo psych’s ability to demonstrate specific hypotheses about how that happened? There, she argues, great skepticism is warranted.

Image: Pleistocene humans stalk a Glyptodon, by Heinrich Harder (1858-1935) / Public domain.