Evolutionary psychology is constrained by evolutionary biology

I’ve had a wonderful time visiting Union College in Schenectady, NY. Faculty invited me to give a talk related to our new paper in Behavioral and Brain Sciences on political bias in social psychology research.

As part of my visit, I chatted with different researchers about adaptive memory, an area that I didn’t know much about. Basically, adaptive memory refers to ways in which our memory processes might be shaped by evolution to perform particularly well on fitness-relevant problems. I mean fitness here in the evolutionary sense of fitness value — the impact of a behavior on reproductive success (which subsumes survival). Given certain facts about humans and the lengthy human maturation process, I like to extend the arc of reproductive success to successfully becoming a grandparent — if you don’t make it to through that gate, it doesn’t matter (unless we’re talking about group or kin selection.)

In talking about adaptive memory, people mentioned previous research by Nairne and colleagues that tested people’s memory for words after rating how relevant those words were to a survival scenario. The scenario said “you are stranded in the grasslands of a foreign land”, and this reference to grasslands is meant to activate some sort of evolved mechanism that enhances one’s memory. The control condition refers to survival in a city in a foreign land, which highlights the researchers’ expectation that “grasslands” should do some work.

I think Nairne and colleagues misunderstand evolution. It would be revolutionary if the word “grasslands” activated something in today’s English-speakers that improved memory performance. Nairne et al. don’t specify a mechanism that would explain their hypothesis. Their discussion of the Pleistocene and their precise grasslands/city contrast imply that they think we have a sort of ancestral memory of life on the savannah, and that activating it has functional consequences. However, such information would have to be both heritable and activated by modern nouns like “grasslands” (and presumably its equivalent in other languages). It’s unclear how this is possible.

Evolved mechanisms were “designed” to solve specific problems that recurred in the ancestral environment. The ancestral environment is not itself a problem. Grasslands are not a problem per se, any more than the Earth is a problem. Invariant features of the environment give no purchase to selection. If human ancestors lived in grasslands over the roughly 2 million years of the Pleistocene, we would not expect an evolved mechanism to activate in the specific presence of grasslands. We’d always be in the presence of grasslands, and such a mechanism would always be activated and could not confer an advantage. For example, nothing would be gained if mating motives were activated by swaying grass, much less by words describing it.

“Grasslands” is no more special a feature of the ancestral environment than starry skies, clouds, rain, fire, or other humans. There’s no reason why we couldn’t use any of those as inductions. For the English word “grasslands” to activate anything, think about how that would work. Since we have no evolved mechanisms tailored to English words, this word must trigger lower level imagery and associations that put us in “go mode”, so to speak, particularly in concert with the survival scenarios the researchers use. Grasslands is a combination of grass and lands, so presumably something about grass or lands, or their semantic union, woud trigger something. It’s not clear what these would trigger that terms like treelands, riverlands, grass, mountains, or Heinz Field would not also trigger. It also requires an activation mechanism that heightens performance over baseline — why would words like grasslands trigger better-than-baseline memory performance? What is the cue signaling exactly?

There are lots of obvious control conditions here. If you think there’s something specific about the ancestral environment that makes these survival scenarios boost memory performance, and you think grasslands describes the ancestral environment in a meaningful way, you’d want to also try mountains, jungles, swamps, deserts, etc. in control conditions. Without those controls, you’ve got no reason to think grasslands means anything special at all. Using cities as a control won’t work — you need to isolate the ancestral environment, not wild vs. urban areas. You’d also want to isolate the effect of survival concerns by using survival scenarios without grasslands or wild areas of any kind.

The survival scenarios puzzled me as well. One example reads:

In this task, we would like you to imagine that you are stranded in the grasslands of a foreign land, without any basic survival materials. Over the next few months, you’ll need to find steady supplies of food and water and protect yourself from predators…

This is supposed to be canonically relevant to fitness — they contend that the situation would stoke tailored memory capacities. However, these scenarios don’t describe recurrent human challenges or the kinds of problems humans had to solve.

Humans are ultrasocial. Our ancestors did not routinely face Survivor-like situations, much less by themselves. They lived in groups. Few humans would ever have been far away from their groups, or stranded for months in another group’s territory. If you were caught in a hostile land, you would simply get back to your own group as fast as possible. There would be no point trying to eek out subsistence for months far away from home — you’d get moving.

There’s little about these scenarios — beyond the gravity and novelty of survival — that should activate powerful memory mechanisms. Good relationships with others in your group would confer more fitness value than your ability to survive alone without tools. If we have memory mechanisms shaped by evolutionary pressures, I would look to interpersonal processes and to simple, recurrent perceptual stimuli, not for responses to English words and solitary emergency scenarios.

All that said, I like the adaptive memory paradigm. Memory should be better for certain types of information, perhaps triggered by certain situational cues. One recurrent problem for an ultrasocial species is recognizing other members of one’s group, so it’s not surprising that we have better memory for faces than for names/words (and, apparently, a region of the brain dedicated to face recognition, the fusiform face area (FFA) — last time I checked at least; neuroimaging is a fast-moving field.)

José L. Duarte recently defended his doctoral dissertation in Social Psychology at Arizona State University. You can email him at jose.duarte@asu.edu.