Adapting evolutionary psychology

5 minute read

I’ve been reading the new paper, “Darwin in Mind: New Opportunities for Evolutionary Psychology”, in PLoS Biology. The paper, by Johan Bolhuis and colleagues Bolhuis:2011, is an extended attack on the methods of analysis that have been most forcefully advanced by John Tooby and Leda Cosmides (mentioned by name) and David Buss (mentioned only by his institution, UT-Austin).

Bolhuis and colleagues focus on four assumptions that underlie some of the hypotheses promoted by researchers like Buss, Tooby and Cosmides:

  1. Humans were once well adapted to their environment (the “environment of evolutionary adaptedness”), but recent changes to human existence have created a mismatch of some human traits with the current environment.

  2. Human cognitive traits evolve slowly and gradually, so that they cannot be well adapted to recent environmental changes.

  3. Human cognition occurs as an outcome of many specialized “modules” in the brain, not a few coordinated and flexible learning mechanisms.

  4. Humans have the same cognitive processes whoever they are and wherever they live – in other words, mental adaptations are universal in humans.

Knowing all of these researchers, I don’t think they would agree with all of this characterization. Some aspects are uncontroversial: Many humans display behaviors that appear poorly suited to current environments but may plausibly have been an advantage in past environments. Others are more reasonable than Bolhuis and colleagues present – for example I know that evolutionary psychologists usually express the “gradualism” assumption in a limited way, assuming that some cognitive adaptations are complex and therefore not likely to have arisen quickly as a result of a simple change in gene frequencies. Likewise, they do not assume that all human psychological traits are universal, but instead that those traits that appear universal are likely to have arisen in ancient environments shared by the ancestors of all humans. In short, I think the paper fails to accurately present the arguments put forward by mainstream evolutionary psychologists.

I’ve written on evolutionary psychology at some length, often in a very critical way (for a good example, check out this post about David Buller’s critical work and evolutionary psychologists’ lame response). But the idea of niche construction irritates me a lot more than evolutionary psychology ever does.

So I’ll take a critical view of the four suggestions put forward by Bolhuis and colleagues as ways to move evolutionary psychology forward:

i) A modern EP would evaluate the evolution of a character by constructing and testing population genetic models, estimating and measuring responses to selection, exploring the covariation of phenotypic traits or genetic variation with putative selective agents, making comparisons across species and seeking correlates to selected traits in the selective environment, and so forth, as do contemporary evolutionary biologists. In addition to these established tools, researchers can also exploit modern comparative statistical methods applied to cultural and behavioural variation [85] and gene-culture coevolutionary theory [22],[58],[83],[86] to reconstruct human evolutionary histories. The function of reliable aspects of human cognition, and of consistent behavioural patterns, can be explored utilizing the same methods. An important point here is that researchers are not restricted to considerations of the current function of evolved traits, and well-established methods are available to reconstruct the evolutionary history of human cognition.

Uh…this is a fancy-sounding paragraph with no concrete suggestion. The response to selection, for example, is determined from heritability and differential reproduction in a particular environment. The paragraph specifically mentions that current functions of traits may be irrelevant to their past evolution. Hence, as evolutionary psychologists have argued, today’s observed differential reproduction and heritability are of limited relevance to the evolution of a trait. Aside from mentioning technical-sounding jargon, this paragraph is simply suggesting that evolutionary psychologists should do scenario-building based on the assumption of past environments of adaptedness. The only novel suggestion (the “gene-culture coevolutionary theory” idea) is that different populations may have different evolved cognitive adaptations. I don’t think many evolutionary psychologists would disagree.

ii) With regard to functional questions, while EP has stressed the idea that human beings are adapted to past worlds [87], a niche-construction perspective argues that human beings are predicted to build environments to suit their adaptations, and to construct solutions to self-imposed challenges, aided and abetted by the extraordinary level of adaptive plasticity afforded by our capacities for learning and culture [88]. While adaptiveness is far from guaranteed, from this theoretical perspective humans are expected to experience far less adaptive lag than anticipated by EP [88]. If correct, examining the relationship between evolved psychological mechanisms and reproductive success in modern environments will not necessarily be an unproductive task.

This is an easy empirical question, it seems to me. The “niche-construction perspective” appears to predict that post-agricultural sedentary humans (living in cities and villages, building and living in structures, working long hours, using a monetary economy, and having vastly higher birthrates) have found ways to replicate a hunter-gatherer lifestyle so that their cognitive adaptations will remain well-adjusted to their current environments. Bolhuis and colleagues point out the rapid rate of Holocene population growth as evidence that we may be comparatively well adapted to these changes.

I disagree. Population growth is merely evidence that our cognitive adaptations have not impeded reproduction. Selection involves differential fertility or mortality, and may be just as strong in a growing population as in a stationary one. I think it is self-evident that some important aspects of the cognitive environment of post-agricultural people are unparalleled in hunter-gatherer societies. I think it is possible that selection has influenced the responses of some people to these environments, and I am very skeptical of the idea of “cognitive universals” in living people. But I don’t think that culture promotes a static, hunter-gatherer-like cognitive niche, or that people have constructed their cultural environments to promote stasis.

The third and fourth points raised by Bolhuis and colleagues are ones with which I basically agree. They note that evolutionary psychologists should do more to investigate the actual neural mechanisms underlying behavior, and that studying development may provide a way to test the evolutionary basis of such mechanisms. These suggestions are non-specific but quite true: To my knowledge, no evolutionary psychologists have ever shown a specific neural mechanism underlying their claims about cognitive “modules”. Instead, they argue by analogy to better-understood cognitive and perceptual systems such as face recognition or visual processing. One of the main reasons why I and other people find evolutionary psychology explanations unconvincing – one that goes back to Gould and Lewontin – is that they fail to engage at the mechanistic level. If these are truly adaptations, then how are they instantiated.

So, at the end, what do I think? To be honest, I really don’t understand the point of an article like this. Bolhuis and colleagues make some good points, but they fail to produce even a single example of a cognitive or psychological trait in humans that can be fruitfully explained using their approach. Indeed, they do not even bother to present a method of hypothesis testing that could satisfy their criticisms.