Can evolutionary psychology evolve?

The Environment of Evolutionary Adaptedness, over a million years ago in the Pleistocene. A founding myth of evolutionary psychology.

In the future, how will we look at evolution and human behavior? Perhaps we’ll still be looking through the lens of evolutionary psychology, albeit a more “evolved” one than the current variety. Or perhaps there will be a new paradigm.

One thing is sure. Evolutionary psychology, as now defined, is untenable. It suffers from several flawed assumptions:

- Human nature is uniform, except for gender differences. It came into existence over a million years ago during the Pleistocene, in the Environment of Evolutionary Adaptedness (EEA). This was long before modern humans began to spread out of Africa some 40,000 years ago and eventually form the populations we know today.

- Given the complexity of human behavior, its genetic basis could not have changed to any appreciable extent since the Pleistocene.

- All present-day humans are therefore essentially the same. All differences in behavior, personality, and temperament must result from a single human nature responding to different environmental inputs.

These assumptions are false. Human genetic evolution has actually accelerated over the past 40,000 years, and even more so over the past 10,000. The latter period, in particular, was not one of people adapting to new physical environments defined by climate, landscape, and vegetation. People were adapting to new cultural environments defined by social structure, normative behavior, and technology.

Yes, human behavior is complex, and any genetic influences must be correspondingly complex. But these influences can be radically changed by a few point mutations. There’s no need to start from scratch, as John Tooby and Leda Cosmides imply. There may simply be changes to developmental timing, such as an infant’s mental plasticity being extended into older life stages. Or there may be changes to the degree of masculinization or feminization. The possibilities are endless. Again, there is no need to posit a huge number of genetic changes.

Yes, we are adapted to past environments—and not to the present one. And there is often a mismatch between something that made sense in the past and our present reality. But why assume a time gap of over one million years? Is it because the Pleistocene makes an ideal setting for just-so stories?

I suspect there is another, more cynical reason. By placing the evolutionary origins of human nature in the distant past, one avoids the messy reality of differences among current human populations—differences in outlook, personality, time orientation, and behavioral predisposition. The Pleistocene EEA may be a just-so story about the past, but it has also had a real impact on the present. It was part of the deal that made evolutionary psychology possible, in the wake of the firestorm that consumed sociobiology.

Will evolutionary psychology evolve?

A paradigm can evolve. Medicine was a pseudo-science that killed more patients than it cured as late as the 1920s. In the space of a few decades, the situation completely reversed. There have been similar turnarounds in other fields. Alchemy became chemistry, and astrology became astronomy.

Indeed, there have been calls for a rethinking of evolutionary psychology, even from Tooby and Cosmides. “Although the hominid line is thought to have originated on edges of the African savannahs, the EEA is not a particular place or time” (Tooby and Cosmides, 2005, p. 22). It is a composite of whichever selection pressures brought each adaptation into existence. There are thus potentially as many EEAs as there are adaptations, and some may be later than others.

This year, several evolutionary psychologists authored what may be called a manifesto for change:

We argue that the key tenets of the established EP paradigm require modification in the light of recent findings from a number of disciplines, including human genetics, evolutionary biology, cognitive neuroscience, developmental psychology, and paleoecology. For instance, many human genes have been subject to recent selective sweeps; humans play an active, constructive role in co-directing their own development and evolution; and experimental evidence often favours a general process, rather than a modular account, of cognition. (Bolhuis et al., 2011)

The text parallels my recent paper in Futures, sometimes strikingly so. It starts off by observing that in the early years of evolutionary psychology “our knowledge of the human genome was limited and gradualism dominated evolutionary thinking.” Today, we know differently:

Events in the Holocene (the last 10,000 years), particularly the adoption of agriculture, domestication of animals, and the increases in human densities that these practices afforded, were a major source of selection on our species, and possibly accelerated human evolution. Evidence from the human genome strongly suggests that recent human evolution has been affected by responses to features of the environment that were constructed by humans, from culturally facilitated changes in diet, to aspects of modern living that inadvertently promoted the spread of
diseases. (Bolhuis et al., 2011)

This recent evolution has especially shaped the human brain: “Genes expressed in the human brain are well-represented in this recent selection.”

Even when assessed on its own terms, the Pleistocene EEA looks more and more like a myth, and should be treated as such:

[…] the abstract concept of stable selection pressures in the EEA is challenged by recent evidence from paleoecology and paleoanthropology. The Pleistocene was apparently far from stable, not only being variable, but progressively changing in the pattern of variation. The world experienced by members of the genus Homo in the early Pleistocene was very different from that experienced in the late Pleistocene, and even early anatomical modern Homo sapiens that lived around 150,000 years ago led very different lives from Upper Paleolithic people (40,000 years ago) (Bolhuis et al., 2011)

Is a paradigm shift in the offing? Probably. But what form will it take? Perhaps the second question is unimportant. Whether evolutionary psychology changes or disappears, we’ll be looking at evolution and human behavior in a very different light.

To be cont’d

References

Bolhuis, J.J., G.R. Brown, R.C. Richardson, and K.N. Laland. (2011). Darwin in mind: New opportunities for evolutionary psychology, PLoS Biol 9(7): e1001109. doi:10.1371/journal.pbio.1001109
http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001109

Frost, P. (2011). Human nature or human natures? Futures, 43, 740–748.
http://dx.doi.org/10.1016/j.futures.2011.05.017

Tooby, J. and L. Cosmides. (2005). Conceptual foundations of evolutionary psychology, in: D. M. Buss (Ed.) The Handbook of Evolutionary Psychology, Hoboken, NJ: Wiley, pp. 5-67.

Mental traits and human variation

An interesting article has come out in Edge by Jonathan Haidt, a University of Virginia psychologist and author of The Happiness Hypothesis. Essentially, he argues that science will soon embrace the idea that human nature evolved not only in the hunter-gatherer environments of the Pleistocene but also in the diverse social environments of the past 10,000 years.

Russian scientists showed in the 1990s that a strong selection pressure (picking out and breeding only the tamest fox pups in each generation) created what was — in behavior as well as body — essentially a new species in just 30 generations. That would correspond to about 750 years for humans. Humans may never have experienced such a strong selection pressure for such a long period, but they surely experienced many weaker selection pressures that lasted far longer, and for which some heritable personality traits were more adaptive than others. It stands to reason that local populations (not continent-wide "races") adapted to local circumstances by a process known as "co-evolution" in which genes and cultural elements change over time and mutually influence each other.

… No new mental modules can be created from scratch in a few millennia, but slight tweaks to existing mechanisms can happen quickly, and small genetic changes can have big behavioral effects, as with those Russian foxes. We must therefore begin looking beyond the Pleistocene and turn our attention to the Holocene era as well - the last 10,000 years. This was the period after the spread of agriculture during which the pace of genetic change sped up in response to the enormous increase in the variety of ways that humans earned their living, formed larger coalitions, fought wars, and competed for resources and mates.

… traits that led to Darwinian success in one of the many new niches and occupations of Holocene life — traits such as collectivism, clannishness, aggressiveness, docility, or the ability to delay gratification — are often seen as virtues or vices. Virtues are acquired slowly, by practice within a cultural context, but the discovery that there might be ethnically-linked genetic variations in the ease with which people can acquire specific virtues is — and this is my prediction — going to be a "game changing" scientific event.

Haidt predicts that the paradigm shift will occur as genome research uncovers evidence that many mental traits differ among human populations. These findings will be unexpected and disturbing to some. “Expectations, after all, are not based purely on current evidence; they are biased, even if only slightly, by the gut feelings of the researchers, and those gut feelings include disgust toward racism.” In making this prediction, Haidt feels some foreboding:

I believe that the "Bell Curve" wars of the 1990s, over race differences in intelligence, will seem genteel and short-lived compared to the coming arguments over ethnic differences in moralized traits. I predict that this "war" will break out between 2012 and 2017.

Gene-culture co-evolution and evolutionary psychology

How much do human populations differ from each other in real, functional terms? The question remains open, but an answer is starting to unfold. In 2007, a team led by anthropologist John Hawks found that natural selection seems to have modified at least 7% of the human genome over the last 40,000 years, i.e., during the period when modern humans spread out of Africa and peopled the other continents. In addition, as they moved into these different physical and cultural environments, the pace of genetic change seems to have speeded up, particularly after the advent of agriculture 10,000 years ago. The rate of change may then have been over a hundred times what it had been during most of human evolution (Hawks et al., 2007)

We do not fully know the nature of these recent genetic changes. John Hawks suggests they may reflect adaptations to new ecological and cultural settings, specifically to cold, to new diets (cereals, milk, etc.), to new epidemic diseases associated with the spread of agriculture (smallpox, malaria, yellow fever, typhus, cholera), and to new forms of “communication, social interactions, and creativity.”

There thus seem to have been multiple EEAs in relatively recent times, and not simply one situated in the Pleistocene. Some of them would correspond to the different physical environments that modern humans moved into as they spread out of Africa 40 to 50 thousand years. Most however, seem to have arisen in the past 10 thousand years and correspond to different cultural environments.

John Hawks is certainly not the first one to suggest that culture has been a key part of the human adaptive landscape. Usually referred to as ‘gene-culture co-evolution’, this paradigm has had many proponents, notably Pierre van den Berghe, Charles Lumsden, and E.O. Wilson. It has nonetheless remained marginal, even among evolutionary psychologists. This is partly because of the influence of John Tooby and Leda Cosmides, whose influence was critical during the early years of evolutionary psychology:

It is no more plausible to believe that whole new mental organs could evolve since the Pleistocene—i.e., over historical time—than it is to believe that whole new physical organs such as eyes would evolve over brief spans. It is easily imaginable that such things as the population mean retinal sensitivity might modestly shift over historical time, and similarly minor modifications might have been made in various psychological mechanisms. However, major and intricate changes in innately specified information-processing procedures presentover brief spans of historical time. (Tooby & Cosmides, 1989)

In a more recent article, they have backed away from this position: “Although the hominid line is thought to have originated on edges of the African savannahs, the EEA is not a particular place or time.” Each biological adaptation has its own EEA, which is simply a composite of whatever selection pressures brought it into being (Tooby & Cosmides, 2005). There are thus potentially as many EEAs as there are adaptations. It follows, then, that some EEAs may have existed later in time than others.

How much later? Tooby and Cosmides considered complexity to be one limiting factor. The more complex the adaptation, the more genes it would involve, and the longer the time needed to coordinate the evolution of all those genes. Therefore, recent biological evolution has probably only involved simple traits, certainly nothing as complex as mental ones. Such traits could have arisen only through a faster process, notably cultural evolution.

The problem with this argument is that complex traits do not arise ex nihilo. They arise through modifications, deletions, or additions to existing traits. And such changes can occur through a single point mutation at a regulatory gene. As Harpending and Cochran (2002) point out:

Even if 40 or 50 thousand years were too short a time for the evolutionary development of a truly new and highly complex mental adaptation, which is by no means certain, it is certainly long enough for some groups to lose such an adaptation, for some groups to develop a highly exaggerated version of an adaptation, or for changes in the triggers or timing of that adaptation to evolve. That is what we see in domesticated dogs, for example, who have entirely lost certain key behavioral adaptations of wolves such as paternal investment. Other wolf behaviors have been exaggerated or distorted.

Gene-culture co-evolution also presents difficulties that are inherent to the paradigm itself:

1. The linkages between genes and culture tend to be remote, indirect, multiple, and complex. There are some straightforward ones, such as between lactose intolerance and consumption of dairy products, but such linkages are probably unrepresentative of gene-culture co-evolution.

2. With only a few minor exceptions, gene-culture co-evolution is specific to humans. Cross-species comparisons, so common in other fields of evolutionary study, are thus of little help (van den Berghe & Frost, 1986).

These difficulties are not insuperable. To some degree, they reflect an unconscious desire to study human evolution with the same conceptual tools that have been used to study the evolution of other species. Other tools will have to be developed, or simply borrowed from the social sciences of psychology, sociology, and anthropology. Thus, there are no real barriers to renewed use of this paradigm, particularly as we move beyond the single-EEA model and investigate this 7% of the human genome that has apparently changed over the past 40,000 years.

References

Harpending, H. & G. Cochran. (2002). "In our genes", Proceedings of the National Academy of Sciences, 99(1), 10-12.

Hawks, J., E.T. Wang, G.M. Cochran, H.C. Harpending, & R.K. Moyzis. (2007). Recent acceleration of human adaptive evolution. Proceedings of the National Academy of Sciences (USA), 104, 20753-20758.

Tooby, J. & L. Cosmides. (2005). Conceptual foundations of evolutionary psychology, in: D. M. Buss (Ed.) The Handbook of Evolutionary Psychology, Hoboken, NJ: Wiley, pp. 5-67.

Tooby, J. & L. Cosmides. (1989). Evolutionary psychology and the generation of culture, Part I. Theoretical considerations, Ethology and Sociobiology, 10, 29-49.

van den Berghe, P.L., & Frost, P. (1986). Skin color preference, sexual dimorphism and sexual selection: A case of gene-culture co-evolution? Ethnic and Racial Studies, 9, 87-113.