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Robert Kurzban

The Evolutionary Psychology Blog

By Robert Kurzban

Robert Kurzban is an Associate Professor at the University of Pennsylvania and author of Why Everyone (Else) Is A Hypocrite. Follow him on Twitter: @rkurzban

EEA = Invariances

Published 4 December, 2012

I’ll be heading off to Belgium on Friday to attend a symposium organized by Johan Braeckman to celebrate the twentieth anniversary of The Adapted Mind, which Wikipedia says “is widely considered the foundational text of evolutionary psychology.” I was flattered to be asked to give a sort of “where are we now” talk at the workshop, so I’ve been thinking a little bit recently in preparation for my remarks about the trajectory of the discipline over the last twenty years.

It is with this in mind that here I consider briefly a post that was called to my attention last week that is otherwise an unremarkable and somewhat meandering instance of the common sorts of poorly founded complaints about evolutionary psychology. The post is by Greg Laden, entitled “Why do men hunt and women shop?”

In the portion of the post I’m interested in, Laden is discussing the argument surrounding the environment in which humans evolved, allowing that “humans are the result of evolution over two million years or so of the Pleistocene,” but later noting that the “Pleistocene is, among recent geological time periods, considered to be the most variable time period that the Earth has ever experienced.” What particularly caught my eye was a passage surrounding the concept of the Environment of Evolutionary Adaptedness (EEA) which, with apologies, I quote here at length. (Apologies more generally for the heavy quoting in this post. My point here is about the positions assumed in this discussion, so I felt it was important to draw on the original text to document these positions.) Here is Laden:

One might argue (and this is the usual argument) that it is really the social setting in which humans lived, not the habitat, that was consistent over two million years, thus the Pleistocene as a variable time period argument goes out the window. But I should point something out about that counterargument: It wasn’t ever made until people like me (mainly me, in fact) started arguing, mainly at conferences, that the Pleistocene varied too much to be thought of as a stable habitat in which certain behaviors would evolve and get “stuck.” You see, part of the Pleistocene argument is that it was a long time compared to the subsequent Holocene (two million vs. 10,000 year) so we are essentially Pleistocene creatures. But when it was pointed out to evolutionary psychologists that the Pleistocene varied tremendously compared to the Holocene, the “oh, it’s the social argument” was raised to salvage the idea.

First, I want to say that I don’t know precisely what time period he’s talking about when he says that he made the argument at conferences that the EEA concept had to include social features as well as the climatological. He might be referring to conferences in the 80’s, in which case his account of history is plausible. This seems unlikely to me insofar as evolutionary psychology as a field didn’t exist in the 80’s, so my sense is he’s got more recent history in mind. In addition, to be fair, I am confident that different scholars have used the term “EEA” in different ways, in print and at conferences, no doubt more or less precisely, and he might well have these other uses in mind. My sense is that he has Tooby and Cosmides at least partly in mind, given that he specifically (if somewhat inaccurately) discusses their cheater detection work in the post, but it’s plausible he is addressing some other account. Fair enough.

Still, if he is talking about the EEA concept around the era of The Adapted Mind, his account would seem to fall short of complete historical accuracy. I found this sociologically interesting because I have frequently encountered confusion about the precise claims about the human EEA, and, as I have noted before, I was also puzzled by the claim that the EEA concept has been updated from the original, without any documentation of the movement from the prior version to the present one.

There are two good sources of the claims regarding what Leda Cosmides and John Tooby meant by their EEA concept, the 1992 “Psychological Foundations of Culture” chapter in The Adapted Mind, and their paper “The Past Explains the Present” in 1990 in Ethology and Sociobiology (now Evolution and Human Behavior). Were they referring to a particular time and a place, a “habitat,” when they discussed the EEA concept, which was then in need of correction by Laden? In 1990, Tooby and Cosmides wrote (p. 387):

The concept of the EEA has been criticized under the misapprehension that it refers to a place, or to a typologically characterized habitat, and hence fails to reflect the variability of conditions organisms may have encountered.

From this it can be seen that even in 1990, they were taking pains to defend against the possibility that careless readers might take them to be saying that the EEA is to be thought of as a time and a place. Instead, they characterize it this way (pp. 386-387):

The “environment of evolutionary adaptedness” (EEA) is not a place or a habitat, or even a time period. Rather, it is a statistical composite of the adaptation-relevant properties of the ancestral environments encountered by members of ancestral populations, weighted by their frequency and fitness-consequences.

They go on to say:

There is no basis in the concept of the EEA for any claims of stasis, simplification, or uniform ancestral conditions in the usual sense. As a complex statistical composite of structurally described contingencies of selection, the idea of an EEA involves no oversimplication. Rather the error is to think that a literal place or a habitat, defined by ostension, is a description of the ancestral condition component of the definition of an adaptation. The concept of ancestral conditions or the EEA, as a statistical composite, is necessarily invoked whenever one is making an adaptationist claim, which means whenever one is making an adaptiveness claim, whether researchers are aware of it or not. As a composite, it is necessarily “ uniform” in the abstract sense, although that uniform description may involve the detailed characterization of any degree of environmental variability. (p. 387)

I suppose that a reader might still be left wondering what sort of statistical composites they had in mind. Did they have in mind properties of only the physical world, particularly those having to do with climate and weather? Any reader left so wondering could note the examples they chose to illustrate. For instance, they discussed the quintessential human social activity, communicating via natural language (p. 388):

The EEA for the human language faculty consists of the statistical composite of relevant environmental features starting from the incipient appearance of the language faculty until it reached its present structure

Later, discussing how adaptations provide evidence about ancestral selection pressures, they wrote (p. 390):

The presence of psychological mechanisms producing male sexual jealousy tells one that female infidelity was part of the human and ring dove EEAs.

From these examples – not to mention the explicit articulation of their view of the EEA concept – it can be seen that Tooby and Cosmides have in mind abstract invariances in the social sphere.  For what it’s worth, in their 1989 article on social exchange, they indeed focus on a social invariance of the EEA, writing that the “ecological and life-history factors characteristic of the human environment of evolutionary adaptedness fulfill the conditions necessary for the evolution of cooperation.” (p. 57)

In the 1992 PFC chapter, they reiterate their commitment to the notion of invariances across multiple domains and, again, in what ought to have defused potential misunderstandings, refer to social dimensions of the world, in this case mental states and emotions (p. 69):

…anything that is recurrently true (as a net statistical or structural matter) across large numbers of generations could potentially come to be exploited by an evolving adaptation to solve a problem or to improve performance. For this reason, a major part of adaptationist analysis involves sifting for these environmental or organismic regularities or invariances. For example, mental states, such as behavioral intentions and emotions, cannot be directly observed. But if there is a reliable correlation over evolutionary time between the movement of human facial muscles and emotional state or behavioral intentions, then specialized mechanisms can evolve that infer a person’s mental state from the movement of that person’s facial muscles

Finally, in case a reader were intimidated by the need to read these admittedly somewhat densely argued scholarly sources, Tooby and Cosmides reiterate their view of the EEA, including the use, again, of a social example (male provisioning) in their online, very accessible primer, dated 1997:

Although the hominid line is thought to have evolved on the African savannahs, the environment of evolutionary adaptedness, or EEA, is not a place or time. It is the statistical composite of selection pressures that caused the design of an adaptation. Thus the EEA for one adaptation may be different from that for another. Conditions of terrestrial illumination, which form (part of) the EEA for the vertebrate eye, remained relatively constant for hundreds of millions of years (until the invention of the incandescent bulb); in contrast, the EEA that selected for mechanisms that cause human males to provision their offspring — a situation that departs from the typical mammalian pattern — appears to be only about two million years old.

In sum, the point is that the EEA concept is, and has been since Tooby and Cosmides began writing about it, defined not as a time or place, not as a claim about the weather or climate, but as invariances, properties across scale, complexity, abstractness, and so forth, that influenced selection of some trait or traits. Somewhat whimsically perhaps, Tooby and Cosmides (1990) provided a sense of just how complex such invariances might be (p. 389):

These invariances can be described as sets of conditionals of any degree of complexity, from the very simple (e.g., the temperature was always greater than freezing) to a two-valued statistical construct (e.g., the temperature had a mean of 31.2 C. and standard deviation of 8.1), to any degree of conditional and structural complexity that is reflected in the adaptation (e.g., predation on kangaroo rats by shrikes is 17.6% more likely during a cloudless full moon than during a new moon during the first 60 days after the winter solstice if one exhibits adult male ranging patterns).

The first “E” in EEA, Environment does not, and has not since Tooby and Cosmides starting using the EEA concept, mean the same thing that “Environment” in “Environmental Science” means. It is emphatically not a claim about the weather. It is emphatically not a claim that there was no climatic variation during the last several million years. The EEA concept is a technical term, and, I concede, its meaning is relatively hard to master. From our imaginations and from such movies as Quest for Fire we can easily and concretely conjure up images of a sort of setting for our human evolutionary past, and this pleasingly concrete image might explain the temptation to construe the EEA that way, as a kind of a concrete stage for our ancestors to act on. This view is not, however, what the concept was intended to refer to. The concept is more abstract, more complex, and more useful than a simple movie set. And it has been since Tooby and Cosmides began using the construct.

Tooby and Cosmides have occasionally referred to the idea that new ideas go through three stages, from: 1) it’s not true; to, 2) it’s true but not important; to, 3) it’s true and important but we knew it all along. The late 80s and early nineties seem to have been the first stage. Twenty years after The Adapted Mind, it seems to me that we’re at a third stage with a twist: it’s true, important, we knew it all along… and now let us instruct you on the ideas you developed twenty years ago.


Cosmides, L. & Tooby, J. (1989). Evolutionary psychology and the generation of culture, Part II. Case study: A computational theory of social exchange. Ethology & Sociobiology, 10, 51-97.

Tooby, J. & Cosmides, L. (1990). The past explains the present: Emotional adaptations and the structure of ancestral environments. Ethology and Sociobiology, 11, 375-424.

Tooby, J. & Cosmides, L. (1992). The psychological foundations of culture. In J. Barkow, L. Cosmides, & J. Tooby (Eds.), The adapted mind: Evolutionary psychology and the generation of culture.New York: Oxford University Press.

  • http://www.facebook.com/laden.greg Greg Laden

    All you had to do was ask me, rather than insinuate that I was making this up! 🙂

    I was at the same institution with Cosmides an Tooby and we shared an advisor. I well remember the talk they gave to people from anthro and psych as a prelude to their launching Evol Psych, and the excitement, well deserved, about Barkow et al being published after that. I attended a series of HBES conferences and “Simian Seminars” (small private meetings) in those days, as well as the usual anthro conferences with a talk on the EEA. Of all the people involved in promoting Evol Psych at the time at Harvard I was one off the few, if not the only, paleo person.

    Subsequent to that I helped John and Leda with a series of experiments using our students at Harvard, to help get the numbers up on some of the early basic tests of how modules might function.

    I still regard “Evolutionary Psychology” as a set of related hypotheses as opposed to a coherent field of study, because it has as its basis a handful of assertions (those are the hypotheses) rather than a handful of questions. Instead of “how do we do X” it is “How does our mechanism for doing X, which we’ll call Z, work?” …. that Z exists and how it comes to be if it does exist are hypotheses in my mind, assumptions in the minds of evol psychologists

    I’ve generally found that when i question that I’m told I’m a science denier or “don’t understand evolution” or am anti-Darwinist, or something a long those lines. Rarely are my questions met with argument or evidence. This disappoints me a great deal. Evol Psych is not without its merits, but it is too full of hubris.

    By the way, do you know the origin of the term EEA? (And no, I’ve not been referring to an earlier use of the term, I’ve been referring to Tooby and Cosmides’ use only… but there is an interesting, earlier origin story for that phrase.)

    • rkurzban

      Thanks for taking the time to comment. Perhaps it’s worth posting a remark in the post to which I’m referring indicating that your criticism of the term dates back to the 80’s, and that in your view, if I understand you correctly, the term has been used as you think it ought to be for the last thirty years or so. As for your question, John Bowlby is frequently credited with coining the term, though I have not specifically looked into its origins in that literature.

      • http://www.facebook.com/laden.greg Greg Laden

        I don’t think the term is uniformly used correctly, that’s the problem. It is a bit of a slippery eel.

        No, it was not John Bowlby. He put it in print first, as a chapter title in fact. I asked Irv DeVore about this one time … he was Tooby’s advisor and mine … and he said to check Bowlby, so I did. But Bowlby has a footnote giving more details. If you have his book, go look it up, you will enjoy the surprise!

        • rkurzban

          Bowlby’s Attachment is searchable on Google Books. Chapter 4 is entitled “Man’s Environment of Evolutionary Adaptedness.” On p. 47, he writes: “This environment I propose to term the system’s ‘environment of adaptedness’.” I didn’t see a footnote along the lines you’re alluding to, but perhaps a reader will be able to identify the passage in question. (On your other remark, David Buss has a nice recent exposition of this idea in his Handbook of Personality chapter, which includes the sentence: “Each adaptation, therefore, has its own EEA.”) Thanks again for taking the time to comment and contribute to this discussion.

      • http://www.facebook.com/laden.greg Greg Laden

        Also, on the EEA; I think it was the original conception, and if not, still the correct way to think about it is that there is not an EEA in which a species lived. There are traits, and traits have EEA’s.

  • http://www.facebook.com/laden.greg Greg Laden

    Oh sorry, forgot to add: It wasn’t just me asking for proper deference to the data on the Pleistocene. John Yellen and Allison Brooks, Ofer Bar Yosef, a few others as well, but I was more likely to attend evol psych meetings and talks because, again, of the overlap in advisor and program.

  • Donald Klein

    Colleagues–The problem is explaining what seems to be an evolved function in terms of the the evolutionary circumstances that made certain forms of natural selection more likely and therefore increase the likelihood of particular evolved adaptations. As I see it the convincingness of the explanation depends on specifying these circumstances– which lately have got bundled under the term EEA.
    However,defining EEA in terms of its relevant evolutionary selection pressures relevant to these effects puts the cart before the horse.To cite from above ,” the environment of evolutionary adaptedness, or EEA, is not a place or time. It is the statistical composite of selection pressures that caused the design of an adaptation.” But that s not explanatory but circular.
    The popularity of caveman behavior type explanations–men hunt-woman tend fire-etc etc is due to relatively clearly (not necessarily correctly) explaining of differential sexual behaviors re relative muscle mass under pre-savagery.
    I think that this advanced definition of EEA serves to confirm the AntiDarwinist view that evolved adaptation is a theoretical given.
    It would really be better to say hat evolutionary causal reconstruction is a naturalistic endeavor that ,given current knowledge,often cannot be accomplished. Maybe later.Some reconstructions imply factual circumstances eg Pleistocene stability-that can be challenged factually .
    This has nothing to do with the fact of evolution and that natural selection is , by far, the leading causal hypothesis.
    Don Klein

  • Tom

    While I’m quite sympathetic with the fully modern usage of the term EEA, I do think John and Leda’s defenders overstate the case that they have always meant for it to have the nuance and flexibility that it now has. The students in my History of Anthropology class are reading Part I of “Evolutionary psychology and the generation of culture” from 1989 (and, by extension, I am re-reading it), and there is no room for doubt that the paradigm they were describing then is one of explaining the present in terms of the Pleistocene. Page after page after page mentions “Pleistocene selection pressures” and the “Pleistocene environment” and “Pleistocene conditions”.

    I don’t think criticisms of Ev Psych on the basis of equating the EEA with the Pleistocene are valid anymore, but I do think it is a bit disingenuous to act as if Tooby & Cosmides & Friends never made that equation. Besides, doesn’t it speak to everyone’s scientific maturity if early evolutionary psychology made a simplistic association between human nature and the Pleistocene specifically, and subsequently corrected itself in light of reasonable criticism?

  • http://twitter.com/Cooldehla CoolDehLa

    So was it Tobias(1965) who first coined the EEA ? See page 59 below, second edition. Reference: http://www.ncbi.nlm.nih.gov/pubmed/17737782

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