Tag Archives: human behavioral ecology

Jones & Bird (2008) == Evolutionary Psychology???

So, I've been spending a bunch of time recently thinking about evolutionary psychology (EP). This is a field about which I have some serious reservations for a variety of reasons both technical and philosophical. That said, I do find the constant in-fighting among human evolutionary biologists tedious and think that it's absurdly unproductive. I am currently working on a critique of some particular aspects of contemporary thought in EP and these blog posts have helped me to get some of my thoughts in order. I am also working on trying to find common ground with researchers in a variety of different "schools" of human evolutionary studies.

Rebecca Bird and I recently wrote a short essay published in Anthropology News that defends functionalist approaches to the study of human ecology (a position that, given the reaction of the editor, is rather controversial). Given the severe length constraints we faced, we were only able to give the barest outline of the research program in human evolutionary ecology that we are trying to establish at Stanford (see this previous post for some details). This is neither the place nor the time to elaborate on the argument of the essay, but I will re-cap a couple points:

  • Contemporary ecological (or environmental) anthropology has ceded explanations of human behavior based on rationality to economists
  • Allowing pure economic (i.e., pecuniary) rationality to define what we collectively consider "rational" is dangerous and ill-considered
  • Expectations of group and/or individual rationality may fail because of a failure to consider the correct objective function, individual heterogeneity, or key trade-offs
  • "Culture" is an amalgam of behaviors and institutions that represent responses to both past and present environments and as such is not particularly useful as a causal explanation for observed behavior

We also suggest some crazy methodological ideas like measuring things and testing multiple competing hypotheses.

The point I want to take up right now is the failure of observing the predictions of rational-actor models because of the failure to account for trade-offs. Rebecca and I had one particular trade-off in mind when we wrote this. We hypothesize that there is frequently a very general trade-off between pecuniary reward and social capital. This arises from the fact that, on the one hand, sharing (especially food-sharing) is so ubiquitous in face-to-face human groups and, on the other hand, people frequently engage in social signaling specifically through economically costly activities (see Bird and Smith (2005) for a review). It would not surprise us at all if it turned out that people were much better at solving complex social optimization problems than they are at optimizing pecuniary return.

Now, in my holiday-induced state of heightened self-reflection, it occurs to me that this argument is really not all that different from Leda Cosmides's (1989, et seq.) suggestion that people are better at solving the Wason selection test when it is presented in terms of social contracts than when it is presented in its traditional way as a test of abstract logical reasoning abilities. Yikes! Does this mean that Rebecca Bird and I are evolutionary psychologists? No, it doesn't. It does make me think that perhaps the time has come for détente among the different schools of thought working on evolution and human behavior. I'm hardly the first person to think this (See Eric Smith's (2000) paper for instance). But maybe I'm the first to blog it!

My Stanford colleagues Rebecca and Doug Bird are clearly leading figures in contemporary human behavioral ecology. I will let their work and the philosophy it entails stand for itself. In what follows, I will focus on my own philosophical and methodological orientation. (Perhaps they will comment on this entry at some point...)

Martin Daly and Margo Wilson (who I think generally do excellent work) rather infamously and imperialistically claimed in a 1999 review article in Animal Behaviour that EP "encompasses work by nonpsychologists, including even those who have deliberately differentiated themselves from 'evolutionary psychology' as 'evolutionary anthropologists', 'human sociobiologists' and 'human behavioural ecologists'." This led to a rebuttal paper by three eminent Human Behavioral Ecologists (Eric Smith, Monique Borgerhoff Mulder, and Kim Hill) (Smith et al. 2000). This is an excellent paper and I heartily recommend anyone interested in evolution and human behavior read the exchange, which is freely available here and here. I will defer to the Smith et al. (2000) paper for the bulk of the arguments on why it is not reasonable to think of HBE (and other approaches) as a subset of EP, but will highlight a couple here:

  • HBE actually pre-dates EP as a field
  • Prominent EP practitioners were the ones who advocated the separation in the first place, largely on theoretical grounds
  • There are substantial theoretical and methodological differences that characterize the two fields

The one issue that I will take up relates to my personal sensibility with regard to science. A tenet of EP is that contemporary behavior -- and the fitness outcomes of this behavior -- is irrelevant for evolutionary understanding. The contention is that we should instead focus on the study of the psychological mechanisms underlying behavior. The idea that current behavior and/or fitness is irrelevant comes across indirectly in Donald Symons's (1989) critique of "Darwinian Anthropology" and more directly and forcefully in Tooby and Cosmides's (1990) follow-up "The Past Explains the Present: Emotional Adaptations and the Structure of Ancestral Environments." I don't want to come across as too much of a de Finetti-style positivist here, but I have a hard time with the idea that we should sacrifice studying observables in favor of objects that we have no hope of observing. While I don't object to studying psychological mechanisms, I do think that since the thing we are interested in explaining is human behavior, perhaps that is what we should study.

But now I find myself confronted with the fact that I have made an EP-like argument in print (albeit Anthropology News!) as well as the very real fact that I have always found Cosmides and Tooby's argument about social reasoning and the Wason selection test compelling. Perhaps the lesson here is that we shouldn't be idealogues with regard to our approach to science. While I will admit a distressingly positivist love of observables (a common feature of Bayesians?), my true philosophical heritage lies in the works of Peirce, James, and Dewey. As a committed pragmatist, I am willing to at least entertain just about any theoretical or methodological position that helps me solve scientific questions.

What if every student of human behavior wrote a paper in which they adopted the approach of a contrasting school? Would this be cool or would it simply be anarchic?

There are some ways in which it is perhaps easier for me to think across these schools than some of my colleagues. My dirty little secret is that I was never really trained in any of them! My graduate training is in (nonhuman) primate behavioral ecology. One of the most influential people for my intellectual and personal development (and probably the only reason I actually got into Harvard) is Irv DeVore, a foundational figure for EP. My Ph.D. advisor Richard Wrangham, while very much a behavioral ecologist when studying chimpanzees, is clearly sympathetic to EP when studying humans. In my post-doc, I moved into more applied questions of human health and population dynamics and indirectly encountered one of the other "schools" of human evolutionary thought, namely, dual-inheritance theory. Cultural transmission models are used in health research to understand the adoption of things like modern contraception or oral rehydration therapy. As a result, I have thought a little about models of cultural transmission (a chapter that I wrote in Melissa Brown's recent book can be found here). This is a pretty natural extension of my work in epidemic modeling and while it is not a central part of my research, I suspect I haven't said my last on the topic (particularly not if I continue to attract clever students interested in the topic).

So, those are my thoughts du jour on the study of human behavior. The winter break is rapidly drawing to a close and pretty soon I will be back in the office and will need to get back to actual research. Hopefully, these meditations in the closing days of 2008 will have a positive influence on this research.


Bird, R. B., and E. A. Smith. 2005. Signaling Theory, Strategic Interaction, and Symbolic Capital. Current Anthropology 46 (2):221-248.

Cosmides, L. 1989. The Logic of Social Exchange: Has Natural Selection Shaped How Humans Reason? Studies with the Wason Selection Task. Cognition 31: 187-276.

Daly, M., and M. I. Wilson. 1999. Human Evolutionary Psychology and Animal Behaviour. Animal Behaviour 57:509-519.

Smith, E. A. 2000. Three Styles in the Evolutionary Study of Human Behavior. In Human Behavior and Adaptation: An Anthropological Perspective, edited by L. Cronk, W. Irons and N. Chagnon. Hawthorne, NY: Aldine de Gruyter.

Smith, E. A., M. Borgerhoff Mulder, and K. Hill. 2000. Evolutionary Analyses of Human Behaviour: A Commentary on Daly & Wilson. Animal Behaviour 60:F21-F26.

Symons, D. 1989. A Critique of Darwinian Anthropology. Ethology and Sociobiology 10 (1-3):131-144.

Tooby, J., and L. Cosmides. 1990. The Past Explains the Present - Emotional Adaptations and the Structure of Ancestral Environments. Ethology and Sociobiology 11 (4-5):375-424.

On Modules

As the next installment in my series on evolution psychology (see previous posts here and here), I thought that I would write about some thoughts on evolutionary modules.  As should be obvious from previous posts, I have serious concerns about evolutionary psychology.  Nonetheless, I don't want to repeat the knee-jerk criticisms that attended the rise of what you might call (and Symons (1989) did call) "Darwinian Anthropology."  Like Anthropology more generally, I have found that the level of discourse in human evolutionary studies tends to be particularly low and this surely hinders progress toward our presumably shared goals of understanding human behavior, the origin and maintenance of human diversity, and how people respond to social, environmental, and economic changes.

In this spirit, I am taking seriously the idea of modularity.  The concept of "massive modularity" seems to be pretty central to just about any definition of modern EP and it is one of the ideas that I see as potentially most problematic.  A major question that naturally arises in the analysis of cognitive modularity is: what is a module?  There are two senses of modularity that you find discussed in the EP literature. For a good review of this, see Barrett and Kurzban (2006). In his highly influential (1983) book, Fodor popularized the concept of a cognitive module.  A Fodorian module is characterized by reflex-like encapsulation of critical functions.  It is thought to be anatomically localized, inaccessible to conscious thought and has shallow outputs.  Our senses and motor systems are examples of possible Fodorian modules, as are the systems that underlie language (Machery 2007).

In contrast to the Fodorian module is the second sense of modularity found in the EP literature, the evolutionary module. Like a Fodorian module, the evolutionary module is domain-specific or informationally encapsulated.  That is where the resemblance ends though.  Rather than being defined by a list of attributes, an evolutionary module is characterized by function.  An evolutionary module is a domain-specific cognitive mechanism that has been shaped by natural selection to perform a specific task.   There is no need here to specify their characteristic operating time, the shallowness of their outputs, or their anatomical localization.

Using engineering-inspired arguments about efficiency and design, the proponents of massive modularity suggest that the brain is really a collection of domain-specific modules.  These modules drive not just the reflex-like actions of our sensory-motor systems but also govern higher cognitive processes like reason, judgment, and decision-making.  The brain is not, as we typically conceive it, a single organ.  Rather it is a collection of special-purpose information processing organs.   Needless to say, such a position has been controversial.  Among the notable critics are Jerry Fodor himself, who wrote a whole book with the sarcastic title (referring to Steve Pinker's (1997) book, How the Mind Works), The Mind Doesn't Work That Way: The Scope and Limits of Computational Psychology.  Another notable critic is David Buller, the ostensible subject of my last two posts.

Barrett & Kurzban (2006) suggest that much of the controversy surrounding the EP concept of massive modularity arises from confusion over what is meant by a module in the EP sense.  That is, critics are thinking about Fodorian modules when the advocates of massive modularity have something entirely different in mind. Maybe.  I'm no expert, but the argument seems plausible for at least part of the controversy.   I have my own issues with modularity but I will save that for the paper that I am writing (and for which these posts serve as sketches to hopefully help me get some thoughts straight).

One point that I will make here is a fairly orthodox criticism of modularity.  In enumerating possible evolutionary modules, and noting that such modules require domain-specific input criteria, Barrett & Kurzban (2006: 630) include "systems specialized for making good food choices process only representations relevant to the nutritional value of different potential food items."  Really? I'm not one to fall back on the weak "culture complicates things" argument, but I do think there are other things -- including ones potentially important for fitness -- involved in food choice than the nutritional quality of a potential foodstuff. Perhaps an anecdote is in order here.

A long time ago, my wife and I were taken out to a fancy Chinese restaurant in Kota Tua, Jakarta by a colleague who wanted to impress us with his esoteric knowledge of a variety of Asian cuisines.  He took the initiative and ordered for the table a range of items including tripe, jellyfish, pig trotters, and chicken feet. For a variety of complex social reasons, we felt it was in our interest to not seem like naïve rubes from America.  So, we ate everything unflinchingly and with smiles on our faces. These were not things we normally would have volunteered to eat (though we now regularly get jellyfish) but the social payoffs of eating these (at the time) unappealing items outweighed whatever distaste we may have experienced.

Clearly, this is a bit of a trivial example.  I nonetheless think that it highlights an extremely important aspect of human decision-making.  The optimal decision in a one dimensional problem may change when one increases the dimensionality of the problem, particularly when the elements of your (vector) optimand trade-off.  Sometimes the optimal nutritional choice is not the optimal choice with respect to social or cultural capital.  The person's foraging decision is presumably one that balances the various dimensions of the problem. In a less trivial example, this is what Hawkes, O'Connell and Bird and Bird are suggesting is going on with some men's foraging decisions  (summarized in this review by Bird & Smith (2005)).  According to their model, men make energetically suboptimal foraging decisions in order to signal their phenotypic quality to political allies and potential mates.  Food choice is thus a decision that balances the potential costs and benefits of at least three fitness-critical domains (energetics, politics, and reproduction).   The same logic can be applied to that other staple of EP, mate choice.  What people say they want on pen-and-paper surveys is not necessarily what they get when they actually choose a mate.  The problem is that one's choice of mate spills over into so many other domains than simply future reproduction.  So it's not simply a matter of the ideal mate being out of one's league.  Sometimes, people actually prefer a mate who does not conform to their ideal physical type.

At the very least, this point seems to require positing the existence of yet another module that integrates the outputs of various lower-level modules.  Of course, this is beginning to sound more like a generalized reasoning process, the bane of EP.

There is another usage of the term "module" that I think may have some relevance to this whole discussion.   In evo-devo, modularity refers to the degree that a group of phenotypic characters have independent genetic architecture and ontogeny.  I will call this an "evolutionary ontogenetic module" (EOM) and contrast that with an "evolutionary cognitive module" (ECM) of EP.  Sperber (2002), in his defense of massive modularity, actually discusses EOMs in passing.  Pigliucci (2008) details the various, largely divergent definitions of modularity.  I tend to think about EOMs the way that Wagner & Altberg (1996) do, wherein a modular set of traits is one with (1) a higher than average level of integration by pleiotropic effects (i.e., gene interactions) and (2) a higher than average level of independence from other trait sets.  That is, modular architecture occurs where there are few pleiotropic genes that act across characters with different functions but more such effects falling on functionally related traits. 

Modularity in the evo-devo sense is central to the evolution of complexity as well as the evolution of evolvability (the capacity of an organism to respond adaptively to selection).  Do ECMs need to be EOMs? Does this and other related concepts from evo-devo help provide a means for relating the ideas of EP or HBE to their genetic architecture and ontogenetic assembly?  I think so but I think an elaboration on this topic awaits a later post.  


Barrett, H. C., and R. Kurzban. 2006. Modularity in Cognition: Framing the Debate. Psychological Review 113 (3):628-647.

Bird, R. B., and E. A. Smith. 2005. Signaling Theory, Strategic Interaction, and Symbolic Capital. Current Anthropology 46 (2):221-248.

Fodor, J. 1983. The Modularity of Mind. Cambridge: MIT Press.

Machery, E. 2007. Massive Modularity and Brain Evolution. Philosophy of Science74: 825–838.

Pigliucci, M. 2008. Is Evolvability Evolvable? Nature Genetics 9:75-82.

Pinker, S. 1997. How the Mind Works. New York: Norton.

Sperber, D. 2002. In Defense of massive modularity. In Dupoux, E.  Language, Brain and Cognitive Development: Essays in Honor of Jacques Mehler. Cambridge, Mass. MIT Press. 47-57.

Symons, D. 1989. A Critique of Darwinian Anthropology. Ethology and Sociobiology 10 (1-3):131-144.

Wagner, G.P., and L. Altenberg. 1996. Perspective: Complex Adaptations and the Evolution of Evolvability. Evolution 50 (3):967-976.

More on Buller and Evolutionary Psychology

This is an ongoing series of meditations on evolutionary psychology inspired by my recent reading of David Buller's piece in Scientific American.  I have been thinking quite a bit in the last year about the relationship between evolutionary psychology, human behavioral ecology, and evolutionary genetics, and maybe these ruminations will help me get my thoughts clear on these difficult topics.  Caveat utilitor: these are not fully formed ideas but the blog is a useful device for organizing my sketches.

I found an interesting  critique of Philosopher of Science and evolutionary psychology critic David Buller's book, Adapting Minds. Edouard Machery and H. Clark Barrett wrote an extended, critical review of Buller's 2005 book in the journal Philosophy of Science.

I must admit that I find myself torn on some of these debates. I am sympathetic to many of the criticisms voiced by Buller, but think that some of the rebuttals are quite compelling as well. For example, Buller is highly critical of work on child homicide by Martin Daly and Margo Wilson of McMaster University.  Daly and Wilson, in a series of famous studies, suggest that child homicide (a rare event) is much more likely to be perpetrated by step-parents (including boyfriends).  The explanation for why this might be relates to the existence of an anti-cuckoldry mechanism in men's brains. Given the enormous obligate investment -- generally on the part of two parents -- entailed in the successful recruitment of human offspring, cuckoldry represents a potentially enormous fitness cost for human men.

In one study of child homicides in Canada between 1974 and 1990, Daly and Wilson calculated a risk-ratio that child homicides are perpetrated by step-parents vs. (putative) biological parents of 123.7.  Buller suggests that such results might simply arise because of ascertainment bias in the reporting of child homicide.  Specifically, he suggests that the cause of death listed on a child's death certificate is far less likely to be homicide if the act was perpetrated by a biological parent. In support of this argument, he cites a paper by Crume et al. (2002) which compared cause-of-death as listed on the death certificate with the cause determined by a interagency multidisciplinary child fatality review team.  This team reviewed child deaths in the state of Colorado and found that a substantial number of likely homicides were not reported as such.  They were then able to investigate which attributes of (alleged) perpetrators made ascertainment more or less likely.  They found that homicides committed by non-relatives (including boyfriends) were 8.41 times more likely to be recorded as such than were those committed by parents. Of 152 death at the hands of parents only 65 were correctly ascertained while 87 were not.  For the 51 deaths attributable to non-relatives, 44 were correctly ascertained while seven were not.  This yields an odds ratio of (44*87)/(65*7)=8.41 that non-relatives will be correctly ascertained compared to parents (the OR changes to 8.71 following multivariate adjustment -- it is this number that is discussed in the various papers). This seems pretty damning (and suggests there are major problems detecting fatal violence against children).  However, one point from this paper that Buller does not note in his critique (at least his 2005 paper in Trends in Cognitive Sciences) is that the odds of ascertainment for non-parent relatives -- including step-parents -- is not significantly different from unity. That is, the group that includes step-parents is as likely to be ascertained as biological parents.  My understanding is that Daly and Wilson's analysis applies to step-parents as well as boyfriends.  The theory certainly predicts this.

My sense is that Buller is reaching a little too far in this critique. While I would hardly consider myself an expert on the topic, I have always thought quite highly of Daly and Wilson's demographic work on homicide.  One of my students is currently relying heavily on their Chicago mortality study published in BMJ.  That is something I do have some expertise in and I think it is excellent.  What I want to know is this: what is the counterfactual to the Daly & Wilson work?  How many child deaths would need to be re-classified in order to have ascertainment bias be sufficient to account for their observed differences?  Daly & Wilson (2007) do just this sort of counterfactual calculation.  They assume that step-fathers are always caught, whereas biological fathers are never caught.  According to their calculation, such a scenario would imply that there were 500 unaccounted-for paternal murders to yield the observed rates.  This is where the problem comes in.  There simply aren't 500 deaths each year to children under five in Canada in that period that aren't due to congenital defects or infectious disease.  Mortality among the young is rare in developed countries. Clearly, not all of the effect that Daly & Wilson report can be attributed to ascertainment bias.  There seems to be some there there.

I think that this over-reaching is a shame.  The critiques that Buller levels in his recent Scientific American piece are serious and deserve to be taken seriously. Here, I specifically mean the idea that an analysis of the Pleistocene will yield significant clues for understanding the design of the human mind and that evolutionary psychology will be much use in helping us understand unique and universal human traits.  The tone of this debate (on both sides) seems to preclude serious consideration of these important concerns.

As I mentioned in my previous post, I find the latter problem particularly troubling because it suggests that there are some things we can never know about human evolution in a scientific way.  Depending on the question, one possible solution to this problem is something Marc Hauser used to talk about in Science B-29 at Harvard.  The problem was how to use evolutionary tools to explain the unique phenomenon of human language.  While human language is clearly a unique, derived trait -- and therefore in a difficult position with respect to scientific explanation -- there are features of human language (e.g., those described by Hockett in his design features of human language) that are shared across multiple species, making them amenable to the comparative method.  If we limit ourselves to specific autapomorphies -- as Buller apparently wants us to when it comes to Human Nature -- then we are sunk.  If we can find features of our cognition that are shared across species and look, as Darwin first suggested, at convergent solutions to similar problems across species, then we may have some hope of understanding the unique whole of human cognition. Of course, we can't do this for cognitive features that have arisen since the Pleistocene because we only have one remnant of the hominin clade left (us).

Regarding our ability to understand the design of the human brain based on our knowledge of the environment of Pleistocene hunter-gatherers, Machery and Barrett (2006: 236) write that Pleistocene hominins experienced a "reduction in sexual dimorphism in body size due to increased pair bonding and male investment in offspring and corresponding reduction in male-male competition." While I happen to agree with this point (and have two new papers either submitted or in prep elaborating my take on this particular phenomenon), it is, in fact, conjectural.  There is nothing to stop us from forming hypotheses about the mechanisms or functional consequences of human behavior that result from this conjecture, and there might be substantial value in doing so.  Nonetheless, I think it's important to note that it is hardly certain that the cause of the reduction in sexual dimorphism among Pleistocene hominins (something we are pretty sure of) was pair bonding.  I'm afraid to say that I am not the least bit confident that we will ever know this for certain.

Why do we think that Pleistocene hominins were "pair bonded"?  We know that sexual size dimorphism is a correlate of mating system.  Polygynous mammals tend to be sexually dimorphic.  The more polygynous, the more dimorphic.  Presumably, this arises through intra-male mating competition, where size matters for the outcome of agonistic encounters.  As detailed in our 1999 paper, the best paleontological evidence we have suggests that there was a substantial reduction in both sexual size dimorphism and dimorphism in canine teeth (another strong correlate of polygyny among Primates) with the emergence of the genus Homo.  This reduction in sexual dimorphism is attributed by many authors, ourselves included, as a signal of a change in mating system toward increased monogamy.  Does monogamy necessarily mean pair-bonding?  Not necessarily. (again, I do think it's true in this case and hopefully, I will finish the paper in which I discuss the details of this argument soon)  There is also the issue that humans are not much different in terms of sexual size dimorphism from chimpanzees, whose mating system is completely promiscuous.  Our teeth may rescue us here.  Chimpanzees are quite sexually dimorphic in their canine teeth.  But how do you weigh the importance of canines as a weapon in a species that makes tools, including weapons that allow it to kill from a distance?

My point here is that there is a good deal of uncertainty about basic aspects of Pleistocene hominin behavior.  This uncertainty is unlikely to ever be completely resolved.  As a result, I'm not convinced that looking for clues about human behavior and the design of the human brain in the behavior of Pleistocene hominins is necessarily the most efficient of productive avenue for understanding our psychology. I don't take the absolutist position that Buller seems to take that there is nothing to be learned about the present by studying the deep past (i.e., it is more than "pure guesswork").  I like the iterative approach of working between hypothesis generation and empirical test that Machery and Barrett describe and think that it sounds an awful lot like the process that most scientists employ in their work and it sounds like the way individuals adapt to dynamic environments.

I'll end this ramble with a question: Do you have to be an evolutionary psychologist to believe in Human Nature?  Buller seems to think so and to think that it's a bad idea.  I don't think of myself as an evolutionary psychologist, but I do think there is such a thing as Human Nature.  I am struck by the fact that despite the dizzying array of cultural diversity that is manifested by our species, a smile is a smile, embarrassment is embarrassment, and a look of consternation is a look of consternation.  We might find different things amusing, mortifying, or distressing but pretty much people everywhere experience these emotions and, because of our theory of mind, recognize them in others.  The work of Eckman, Eibl-Eibesfeldt, and Fernald, to name a few, is pretty compelling in this regard.  Do we have a cheater-detection module that was engineered in the Pleistocene?  Maybe.  Honestly, I don't care that much, but I do think that denying the existence of Human Nature is done at our collective peril.


Buller, D. J. (2005). Evolutionary psychology: the emperor's new paradigm. Trends in Cognitive Sciences, 9(6), 277-283.

Crume, T. L., DiGuiseppi, C., Byers, T., Sirotnak, A. P., & Garrett, C. J. (2002). Underascertainment of Child Maltreatment Fatalities by Death Certificates, 1990–1998. Pediatrics, 110(2), 1-6.

Daly M, Wilson M (2007) Is the "Cinderella effect" controversial? A case study of evolution-minded research and critiques thereof. In C Crawford & D Krebs, eds., Foundations of evolutionary psychology. Mahwah NJ: Erlbaum.

Machery, E., & Barrett, H. C. (2006). Essay Review: Debunking Adapting Minds. Philosophy of Science, 73, 232-246.

Wilson, M., & Daly, M. (1997). Life expectancy, economic inequality, homicide, and reproductive timing in Chicago neighbourhoods. British Medical Journal, 314(7089), 1271-1274.

Buller on Evolutionary Psychology

Relentless critic of evolutionary psychology, David Buller recently wrote a piece in Scientific American outlining the critique he has developed over the last several years against this particular flavor of human evolutionary studies.  The author of Adapting Minds lists four ideas from contemporary evolutionary psychology (EP) that he suggests are fallacious:

  1. Analysis of Pleistocene Adaptive Problems Yields Clues to the Mind’s Design
  2. We Know, or Can Discover, Why Distinctively Human Traits Evolved
  3. “Our Modern Skulls House a Stone Age Mind”
  4. The Psychological Data Provide Clear Evidence for Pop EP

In my graduate seminar on Evolutionary Theory for the Anthropological Sciences, we read Buller's more technical (2005) critique of EP.  I find myself largely in agreement with his criticisms and, importantly, when I disagree with him, I think it is for interesting reasons.  

The first of these critiques is, in my opinion, the most far-reaching and damning. The Pleistocene, the geological epoch that lasted from around 1.8 million to 10,000 years before present, takes on the role as a mythical age of creation for EP. You see, the Pleistocene represents out species "Environment of Evolutionary Adaptedness" (EEA), a concept derived from developmental psychology and particularly John Bowlby, the father of attachment theory.  In the words of Tooby and Cosmides (1990: 386-387), the EEA "is not a place or a habitat, or even a time period.  It is a statistical composite of the adaptation-relevant properties of ancestral environments ecounted by members of ancestral populations, weighted by their frequency and fitness-consequences."

The key question, as Buller notes, is what would such a statistical composite look like for humans?  The insight that is regularly trotted out is that humans (hominins really) were everywhere hunter-gatherers until about 10,000 years ago -- and were mostly hunter-gatherers for some substantial period after that! So, what do we know about hunter-gatherers?  Much to our collective loss, most of what we know about hunter-gatherers comes from the study of highly marginalized populations.  This is because states, with their potential economic surpluses, large populations sizes, and hierarchical social organization (read: efficient militaries) pushed hunter-gatherers into marginal habitats throughout the world as they moved across the landscape.  Nonetheless, the hunter-gatherer populations that we know about are a remarkably diverse lot.  A terrific reference cataloging some of this diversity is Robert Kelly's (1995) The Foraging Spectrum.  In my specific area of interest (i.e., biodemography), Mike Gurven and Hilly Kaplan have recently written a very interesting paper on the diversity of hunter-gatherer patterns of mortality.  In this figure, taken from Gurven and Kaplan's paper, we can catch a glimpse of the variability just in hunter-gatherer demography.

Humans are clearly quite different from chimpanzees.  The point of Gurven and Kaplan's paper is that the existence of elderly within our societies is not simply an artefact of the modern industrialized world.  Old-age is as much a part of the human life cycle as is childhood.  Given the long potential lifespans of people in all the sampled populations, there is nonetheless a remarkable diversity in life expectancy (the average number of years lived by a person in the population) portrayed in this figure, considering that these are all groups without access to modern medicine.  There are people who live in arid lands of Sub-Saharan Africa (!Kung, Hadza), South American forests (Ache, Tsimane, Yanomamo) and South American grasslands (Hiwi).  Life expectancy at age 5, (\stackrel{\circ}{e}_5) varies by as much as 30%.  The basic point here is that even in something as basic as age-specific schedules of mortality and fertility, different hunter-gatherer groups are very different from each other (note that the Ache and !Kung differ in their total fertility rates by a factor of nearly two).

In all likelihood, our Pleistocene ancestors, like the sample of hunter-gatherer societies discussed in Kelly (1995) or Gurven and Kaplan (2007), lived in diverse habitats, engaged in diverse economic activities within the rubric of hunting and gathering, had diverse social structures, met with diverse biotic and abiotic environmental challenges to survival and reproduction, and dealt with diverse hostile and harmonious relations with conspecifics outside of their natal groups or communities. In other words, it's hard to imagine what neat statistical generalizations about hunter-gatherer lifeways -- and the selective forces they entailed -- could emerge from such diversity. People lived in face-to-face societies.  People had to integrate disparate sources of information to make decisions about fundamentally uncertain phenomena. There was probably a sexual division of labor, though not necessarily the same one everywhere. There were women and men. Probably some other things too, but not that many.  Robert Foley (1996) has a nice critique of what he sees as an extreme simplification of the Pleistocene hunter-gatherer lifeways under the rubric of the EEA.  

Another related problem with the EEA line of thinking is this idea that somehow selection stopped when humans developed agriculture.  10,000 years, while brief in the grand scheme of things, is still not exactly evolutionary chump change.  That span represents anywhere from 350-450 human generations.  This is, in fact, plenty of time for selection to act.  We know from genome scans done in the lab of Jonathan Pritchard, for example, that there is extensive evidence for rapid, recent selection in humans. New, complex psychological mechanisms?  Probably not, but we should nonetheless not fall into the trap of thinking that somehow evolution stopped for our species 10,000 years ago.

Buller's second fallacy ("We Know, or Can Discover, Why Distinctively Human Traits Evolved") is a deeply difficult problem in human evolution. I'm afraid that my current thinking on this problem leads me to the same pessimistic conclusion that Buller and his colleague Jonathan Kaplan come to: There are just some things that we can't know (scientifically) about human evolution.  This arises from the fact that our species is the only member of our genus and we are separated from our sister species by nearly six million years. As Dick Lewontin first noted in 1972, despite our dizzying cultural and social diversity, we are an amazingly homogenous species genetically.  I suspect that what this means is that the standard conceit of EP (one that Buller is highly critical of), that humans are everywhere the same critter, is probably true.  Unique (and universal) phenomena present science with a particular explanatory challenge. Buller is spot on when he criticizes EP for wanting it both ways.  On the one hand, EP sees a robust and universal human nature (an idea to which I am sympathetic, by the way).  On the other, EP sees strong selection driving the evolution of diverse psychological mechanisms.  The unpleasant reality is that if selection on psychological mechanisms were, in fact, that strong and pervasive, we should expect contemporary heterogeneity in the expression of such adaptations across different populations.  This is a topic that University of Illinois anthropological geneticist Charles Roseman and I have talked about quite a bit and have a very slowly gestating manuscript in which we discuss this and other ideas.  I know of no convincing evidence that such variation exists and for this and other reasons, I remain a steadfast skeptic of the idea that natural selection has shaped all these important psychological mechanisms independently and with precision to the tasks to which they are supposed to represent engineering solutions.

Buller's argument for fallacy #3 (“Our Modern Skulls House a Stone Age Mind”) is, I think, a little unfair.  The major argument he makes on this point is that some of our psychological mechanisms did not, in fact, arise in our Pleistocene hunter-gatherer ancestors, but are of a more ancient, primate (or even mammalian) nature.  Honestly, I doubt that this point would elicit many complaints by anyone of the so-called Santa Barbara school. Sometimes critics -- myself included -- make a little too much of the it-all-evolved-in-the-Pleistocene bit.  I think this is one example of that.  Tooby and Cosmides have themselve argued that the EEA can be thought of as working at a variety of time scales.  The emotional systems described by Jaak Panksepp and used by Buller in his critique -- Care, Panic and Play -- are all pretty basic ones for a social species.  Indeed, the emotional system of panic almost certainly pre-dates complex sociality.  The EEA argument, as laid out by John Tooby and Irv DeVore (1987) and then by Tooby and Cosmides (1990), is essentially one of evolutionary lag: complex adaptations to past environments are carried forward into the present.  When a system retains its function, the scale of such lag can be large.  Think about bilateral symmetry or the tetrapod bauplan. I think that a fair assessment of Santa Barbara style EP reveals that there is nothing contradictory about the existence of primitive (in the sense of pleisiomorphic) emotional systems in contemporary humans.

Another small point of departure between Buller's critique and my own thinking on the matter is his discussion of David Buss's work on sexual jealousy.  Now, I should be perfectly clear here.  I happen to think that the whole sex-differences in sexual preferences thing is the most overplayed finding in all of evolutionary science.  In class, I refer to this work as Men-Are-From-Mars Evolutionary Psychology.  The basic idea is to take whatever tired sexual stereotype that you'd hear in a second rate stand-up comedian's monologue, or read about in airport bookstore self-help tracts and dress it up as the scientifically proven patrimony of our evolutionary past.  Ugh.  No, the part of Buller's argument with which I disagree is his apparent take on decision-making. Buller writes, "According to Pop EP, many cultural differences stem from a common human nature responding to variable local conditions."  I guess I'm not so clear as to what's wrong with such a statement.  Isn't that really what he argues in the previous paragraphs when he suggests that women and men have a fundamentally similar reaction to sexual jealousy?  On this he writes, "Instead both sexes could have the same evolved capacity to distinguish threatening from nonthreatening infidelities and to experience jealousy to a degree that is proportional to the perceived threat to a relationship in which one has invested mating effort."  An evolutionary psychology that took seriously environmental (including cultural) variability and combined it with some preferences over risk and uncertainty and a generalized calculus of costs and benefits: Now that would be interesting!  Of course, I'd call that behavioral ecology.

Regarding fallacy #4 ("The Psychological Data Provide Clear Evidence for Pop EP") more generally, I think that Buller is right on.  The evidence for many of these so-called psychological adaptations is pretty weak.  There is general contempt for population genetics among the smarter (and there are smart ones) evolutionary psychologists with whom I have talked and general ignorance among the less gifted.  I think this contempt and/or ignorance is expressed to the detriment of scientific progress in EP.  Buller's point that cross-cultural differences are sometimes greater than inter-sexual differences in the psychological traits that are putative adaptations for sex-specific reproductive strategies, while not specifically substantiated, is pretty devastating.  This is where population genetics comes in.  Thinking about within vs. between population variance is a very important step in understanding the evolutionary forces at work.

The complex organ that is the human brain is certainly the result of selection.  As George Williams reminds us, selection is the only evolutionary mechanism that can produce this type of complexity. So, like Buller, I agree that there must be an evolutionary psychology.  Our various complaints are with the evolutionary psychology that Buller labels "Pop EP."  It's all too easy to be critical. Developing scientific theories for phenomena as complex as those surrounding the evolution of our species is a difficult task and takes ingenuity, courage, and, of course, thick skin. Among the various practitioners of EP of whom Buller is particularly critical, I think that John Tooby and Leda Cosmides are smart people who manifest all these qualities.  A fallacy of contemporary discourse -- one that is all too easily seen in anthropological meetings --  is that people who disagree intellectually must hold each other in contempt or otherwise dislike each other.  I disagree with much of current EP but I also think there are some interesting ideas among practitioners of EP, once we get beyond the trite Men-Are-From-Mar/Women-Are-From-Venus stereotypes.

Detailing where I think the action is in an interesting evolutionary psychology is at the very least another long blog post.  Some areas that I think are promising and/or under-studied include: detailed analyses of cultural transmission dynamics, understanding how people integrate diverse types of information to form decisions with fitness consequences, and understanding how people weigh risk and uncertainty.  I have a lot more to say on these topics, so I think it will have to wait for future posts...


Buller, D. J. (2005). Evolutionary psychology: the emperor's new paradigm. Trends in Cognitive Sciences, 9(6), 277-283.

Foley, R. (1996). The adaptive legacy of human evolution: A search for the environment of evolutionary adaptedness. Evolutionary Anthropology, 4, 194-203.

Gurven, M., & Kaplan, H. (2007). Longevity Among Hunter-Gatherers: A Cross-Cultural Examination. Population and Development Review, 33(2), 321–365.

Kelly, R. L. (1995). The Foraging Spectrum: Diversity in Hunter-Gatherer Lifeways. Washington DC: Smithsonian Institution Press.

Lewontin, R. C. (1972). The apportionment of human genetic diversity. Evolutionary Biology, 6, 381-398.

Voight, B. F., Kudaravalli, S., Wen, X., & Pritchard, J. K. (2006). A map of recent positive selection in the human genome. PLoS Biology, 4(3), e72. Epub 2006 Mar 2007.

Tooby, J., & Cosmides, L. (1990). The Past Explains the Present - Emotional Adaptations and the Structure of Ancestral Environments. Ethology and Sociobiology, 11(4-5), 375-424.

Tooby, J., & DeVore, I. (1987). The reconstruction of hominid behavioral evolution through strategic modeling. In W. Kinzey (Ed.), Primate Models of Hominid Behavior. Stony Brook: SUNY Press.

On Abolishing "Darwinism"

Olivia Judson has written another installment in her series celebrating Charles Darwin.  In this one, she suggests that we should lose the term "Darwinism" and all its variants.  I think that she argues convincingly that labeling the scientific enterprise of modern evolutionary biology as "Darwinism" implies that the field is static, indeed, "that the subject hasn’t changed much in the 149 years since the publication of the Origin." Of course, nothing could be further from the truth and the obsession with questions of the form "Was Darwin Right About X?" plays into the hands of anti-rationalist, anti-science creationists. 

Frequently, I have been bothered by the cult of Darwin that one finds among a certain kind of evolutionary thinker and it's nice to see Judson calling this out. 

There is an interesting dynamic that played out in the area of human behavioral biology in the late 1980s and early 1990s.  At the time, there was a feud developing between scientists who studied the present-day consequences of variation in human behavior and those more interested in the design of the organ that leads to behavior, the brain.  In a provocative paper written in 1989, Donald Symons of the University of California Santa Barbara suggested that "adaptive design is usually manifested at the psychological rather than at the behavioral level, that measuring reproductive differentials is at best an inefficient and ambiguous way to illuminate adaptation, and that Darwin's theory of natural selection sheds light on human affairs only insofar as it promotes understanding of the psychology that underpins these affairs."  (there's that ownership of natural selection again) Needless to say, this paper did not go over well with people who actually chose to measure the present-day consequences of behavior (e.g., on reproductive success) and a bit of a flame war broke out in the pages of the journal Ethology & Sociobiology (the official publication of the Evolution and Human Behavior Society and later to be renamed Evolution and Human Behavior).

What is so interesting about this debate is how, in good segmentary fashion, the two sides desperately tried to claim Darwin as the founding mythological patriarch of their lineage.  A science true to Darwin's legacy would variously study behavior or study psychology depending upon whether one was a Darwinian Anthropologist or a Darwinian Psychologist (Symons's terms, though I should note that to this day, at least a plurality of evolutionary psychologists reside professionally in anthropology departments). This debate continues, albeit a little less raw.  I list a number of key papers in this debate below.  We read these in my graduate seminar on evolutionary theory in the anthropological sciences. 

So I support Judson's call to drop the term "Darwinism" (or "Darwinian") from our regular scientific vocabulary. As she cleverly argues, we don't refer to fixed wing aeronautical engineering as "Wrightian" aeronautics, despite the fact that the field was established by the Wright brothers. Use of the patronym plays into the hands of  creationists.  It also makes it too easy to forget that evolution is effected by more than simply "Darwin's" natural selection.  There is (the other) "Wrightian" genetic drift. Or mutation. Or even something as prosaic as migration (dare I call it "Cavalli-Sforzian"?). Science should strive to transcend the cult of personality. I, for one, would like to see less political and religious jockeying to see which tradition can be more true to its mythological "Darwinian" patriarch and more focus on actually doing science.  But I guess that just shows that I remain naïve about human nature.


Symons, D. 1989. A Critique of Darwinian Anthropology. Ethology and Sociobiology 10 (1-3):131-144.

Tooby, J., and L. Cosmides. 1990. The Past Explains the Present - Emotional Adaptations and the Structure of Ancestral Environments. Ethology and Sociobiology 11 (4-5):375-424.

Betzig, L. 1989. Rethinking Human Ethology: A Response to Some Recent Critiques. Ethology and Sociobiology 10 (5):315-324.

Turke, PW. 1990. Which humans behave adaptively, and why does it matter? Ethology and Sociobiology 11 (4-5):305-339.

Tooby, J., and L. Cosmides. 1989. Evolutionary Psychology and the Generation of Culture .1. Theoretical Considerations. Ethology and Sociobiology 10 (1-3):29-49.

On Culture and Ecological Anthropology

Following up on a thread still circulating on the EANTH List, the question arose of how essential is the concept of culture for defining ecological anthropology. In an earlier post, I had objected to the idea that culture lies at the center of ecological anthropology. For instance, most scholars coming out of an ethological tradition (e.g., primatologists, human behavioral ecologists) see behavior as the focus of their analysis. Especially important for primatologists are relationships, which scale to yield social structure, an idea quite distinct from culture. In the continuing debate on EANTH-L, a suggestion was made that while culture may not be important for primatologists, primatologists are an abject minority of ecological anthropologists and therefore are not really relevant for defining the field. Without "culture" in the definition, ecological anthropology loses its heart. No mention was made of human behavioral ecology (HBE). Here, I post an edited version of my latest contribution to this debate in which I specifically address the role of HBE in ecological anthropology.

It is not just the primatologists among us anthropologists for whom culture is secondary. Surely, most anthropologists (at least in the United States) are primarily interested in culture. But defining a field based on the majority practice is rather hegemonic, no? Human behavioral ecologists, a group of scholars mentioned in the big-tent description of ecological anthropology also focus their analysis on behavior, and specifically decision-making. Culture may play a role in such decision-making processes, but it need not. Some HBE contributers to major questions of interest to ecological anthropologists, broadly construed, include: Mike Alvard on hunting and indigenous resource conservation, Smith and Wishnie on the relationships between conservation and subsistence, Rebecca Bliege Bird and Doug Bird on Aboriginal burning, successional dynamics and subsistence, Bram Tucker on subjective discounting, etc. I list some references following this text of work by human behavioral ecologists who are certainly not on the margins of what I would call ecological anthropology. None of these works rely on the analytic concept of culture as a primary explanation.

Those of us trained in the British Social Anthropology tradition may also be able to relate to a certain ambivalence toward the concept of culture. Though a primatologist by training, I find myself as much influenced by the Manchester School of Social Anthropology (e.g., Max Gluckman, John Barnes, Elizabeth Bott) as I am by Robert Hinde. Both primatologists (with their ethological background) and social anthropologists of the British School focus their analysis on social structure that arises through relationships and other social interactions. It was, after all, the Manchester school that gave rise to the field that came to be known as social network analysis, despite the fact that this field is generally associated with sociology today.

So, yes, by all means let's pitch a big tent for what we call ecological anthropology, but let's also cast our definitions of what counts as ecological anthropology in such as way as to be truly inclusive of the various historical traditions within anthropology. Recasting the suggested definition of ecological anthropology somewhat to account for this broader definition, I propose something like:

Ecological anthropology takes as its field of study the role of culture, social structure, and human agency in explaining the dynamic interactions between human populations and the ecosystems in which they are embedded.

This is a rough first approximation. I would like to work in Andrewartha and Birch's definition of ecology as being the distribution and abundance of species in there as well, but that's for another day...

Selected References.

Alvard, M. S. 1998. Evolutionary ecology and resource conservation. Evolutionary Anthropology 7 (2):62-74.

Bird, D.W., R. Bliege Bird, and C.H. Parker. 2005. Aboriginal burning regimes and hunting strategies in Australia’s Western Desert. Human Ecology 33: 443-464.

Bliege Bird, R. (2007) Fishing and the sexual division of labor among the Meriam. American Anthropologist 109:442-451.

Borgerhoff Mulder, M., Caro, T and A. O. Msago. 2007. Integrating anthropological, archeological, biological and historical research in a long term conservation study in the Katavi ecosytem. Conservation Biology 21(3): 647-658.

Gurven, M.D., K. Hill, H. Kaplan, A. Hurtado, R. Lyles. 2000. Food transfers among Hiwi foragers of Venezuela: tests of reciprocity. Human Ecology 28(2):171-218.

Hinde, R. A. 1991. A Biologist Looks at Anthropology. Man (n.s.) 26 (4):583-608.

Ruttan, L. M. and M. Borgerhoff Mulder. 1999. Are East African pastoralists truly conservationists? Current Anthropology 40(5):621-652.

Smith, E. A., and M. Wishnie. 2000. Conservation and subsistence in small-scale societies. Annual Review of Anthropology 29:493-524.

Tucker, B. 2006. A future discounting explanation for the persistence of a mixed foraging-horticulture strategy among the Mikea of Madagascar. In Behavioral Ecology and the Transition to Agriculture, edited by D. J. Kennett and B. Winterhalder. Berkeley: University of California Press.
Pp. 22-40.

Tucker, B. and L. Rende Taylor 2007. The human behavioral ecology of contemporary world issues: Applications to Public Policy and International Development. Human Nature 18(3): 181-189.

Winterhalder, B., and F. Lu. 1997. A forager-resource population ecology model and implications for indigenous conservation. Conservation Biology 11(6): 1354-1364.