Buller on mental adaptations

11 minute read

I'm reading through David Buller's Adapting Minds : Evolutionary Psychology and the Persistent Quest for Human Nature. It's a back-burner read for me; I pick it up when it's time for the twins to nap. Still, it is hard to put it down in the middle of a chapter.

The book is a critique of evolutionary psychology as practiced now, and an attempt to redirect the field to a better evolutionary grounding. I should mention that throughout Buller refers to "evolutionary psychology as commonly practiced now" as "Evolutionary Psychology" with a big "EP". This is because he has the ambition of establishing an "evolutionary psychology" with a little "ep" by purging all the flaws of the present form. I find this very irritating myself; I would rather he just have come up with another name, just as the "Evolutionary Psychologists" came up with that to replace "sociobiology". So I will try to avoid this confusion by never referring to the field as it "should" be, but only as it exists.

In any event, Buller has an admirable thesis. Unlike other critics, especially Stephen Jay Gould, Buller does not believe that evolutionary psychology has a fatal flaw. Nor does he look for one; he is basically sympathetic with the aims and scope of evolutionary psychology. Instead, Buller thinks that almost every one of the substantive claims of evolutionary psychology are wrong, and that the problems lie in the details of these arguments. So he sets out to deal EP the death of a thousand cuts: outline the major empirical claims of evolutionary psychologists, and explain one-by-one why they are wrong.

That's not to say that Buller himself is right about everything. I'll probably write about my problems with chapter 4 ("Modularity") before long.

But chapter 3 ("Adaptation") is downright inspiring as an example of cut-to-the-bone evolutionary criticism. This chapter is the first real substantive criticism, following an explication of the goals and project of evolutionary psychology as it exists today.

This criticism begins by problematizing the concept of the "environment of evolutionary adaptedness" (EEA). There is little new here; although a specification of such an environment would be desirable in terms of identifying the adaptive problems faced by prehistoric people, there is no reason to suppose that Pleistocene humans faced environments that were spatially or temporally consistent enough to allow such specification.

Constructing adaptive problems

To me, the first significant point Buller presents concerns the "grain" of adaptive problems --- essentially the extent to which a problem must be described in terms of specific subtasks that an organism must perform. Here is his description:

As Tooby and Cosmides would argue, we can be quite confident that Pleistocene humans would have had to "select mates of high reproductive value" and to "induce potential mates to choose them," for example.
But here we encounter a problem concerning the "grain" at which these adaptive problems are described. It is true that we can always be certain that just about all sexually reproducing species face the adaptive problems of selecting mates of high reproductive value and inducing potential mates to become actual mates. These descriptions of adaptive problems are so course-grained, however, as to be wholly uninformative about the selection pressures that act on a species. Consider, for example, what one need do to attract a mate. Male bowerbirds must build ornately decorated bowers, male hangingflies must offer captured prey as a nuptial gift, and male sedge warblers must sing a wider repertoire of songs than other males. The adaptive problem of attracting a mate thus takes very different forms depending on the species... (Buller 2005: 97).

Buller goes on to describe the subtasks involved in such adaptations as consequences of species-typical psychologies. The main argument here is that we have no a priori knowledge about the adaptive problems faced by early humans, without taking into consideration substantial assumptions about their psychology.

For the anthropologist, a closely analogous problem is the hunting-vs-scavenging debate for early Homo. We can imagine the adaptive context of Late Pliocene environments including packets of meat on the hoof and packets of carrion at various stages of consumption by carnivores and scavengers. We can imagine the adaptive challenges of tracking and killing animals on the one hand, and of fighting off lions and hyenas on the other. But whether humans hunted or scavenged depends not only on these paleoecological considerations but also on human psychology itself. Humans do not hunt only for digestive satisfaction; they also do so for social prestige. This is not a recent development. Indeed the most widely-held hypothesis for the development of meat-eating (whether hunted or scavenged) is that males began providing meat as a way to provision females or dependent offspring. If the origin of meat-eating itself lies in social change, then the psychology of the first meat-eaters is an essential part of the adaptive context in which meat-eating arose. An assumption of optimal foraging may easily be wrong if the hominids are optimizing their social benefits rather than their acquisition of calories -- a distinction that becomes even more important for later hominids who hunt prime-age animals instead of the sick and weak.

Buller cites a passage from Richard Lewontin, which rings true for hominids when hominids and marrow-bones are substituted for thrushes and snails:

Indeed, the morphology and psychology of a species determine which aspects of the environment are adaptive relevant to the species. As the biologist Richard Lewontin says: "The bark of the trees is part of the environment of a woodpecker, but the sontes lying at the base of the tree, even though physically present, are not. On the other hand, thrushes that break snail shells include the stones, but exclude the tree from their environment. If breaking snail shells is a 'problem' to which the use of a stone anvil is a thrush's 'solution,' it is because thrushes have evolved into snail-eating birds, whereas woodpeckers have not. The breaking of snails is a problem created by the thrushes, not a transcendental problem that existed before the evolution of the Turdidae." (Buller 2005:98, citing Lewontin 1983:76)

After this Buller turns to the consideration of the evolution of social intelligence within a changing social environment, niche construction, and other reasons to think that the adaptive problems faced by prehistoric humans were far from stable, but instead were constantly changing. In this part, he makes an important point: that "adaptive problems" don't force a solution. Populations do just fine without solving adaptive problems, even if a solution might increase their adaptation by causing them to spread at the expense of other populations. The point is, that even if we could identify the adaptive problems faced by Pleistocene humans, we would have no reason to think they evolved adaptations to deal with those problems. The adoption of sign language might solve some adaptive problems for wild chimpanzees, but that doesn' t mean that the behavior necessarily will arise, nor that the fate of chimpanzees particularly hinges on it.

And there is this Gouldian passage:

Since selection builds solutions to adaptive problems by retaining modifications to preexisting structures, the form of a solution -- an adaptation -- will always be a function of the possible ways in which the preexisting structure could be modified. Consequently, we can never infer the structure of an evolved solution to an adaptive problem from the nature or the problem itself. We also need to know something about the preexisting structure that was recruited and modified to solve the problem. But, as argued previously, we simply don't know what kinds of preexisting psychological characteristics our ancestors possessed (Buller 2005:104).

The point of the section is that we cannot assume any a priori knowledge about past adaptive problems at all. We must begin with a substantial knowledge of our psychology in the first place. So the idea that we can infer psychological adaptations merely because of the adaptive problems that "must have" occupied our ancestors is fallacious. Buller argues that if we claim that humans have psychological adaptations, we must do so on the basis of human psychology as we observe it, not on the basis of presumed past adaptive problems.

Building complex adaptations

The other reason evolutionary psychology proposes for the necessity of considering the EEA is the idea that designing human psychological adaptations would require a lot of time. If this assertion were true, it would imply that humans are adapted to Pleistocene life but not more recent environments -- there just would not have been enough time for people to develop adaptations to recent environmental changes, like the development of agriculture and complex societies.

But this assertion is simply false, because as Buller points out it makes the false assumption that new psychological adaptations must be designed from scratch whenever the environment changes. If we instead imagine that selection need only modify existing adaptations, then there is no need to imagine that humans are still adapted to Pleistocene conditions. There has been plenty of time for selection to exert marked changes on human populations, as exemplified by the evolution of lactase persistence in some populations and the evolution of malarial resistance in others. Indeed, the recently selected alleles at the ASPM and Microcephalin loci may reflect changing psychological adaptations over a recent time span.

The psychic unity of humankind

By far my favorite part of the chapter is Buller's dismantling of the idea that human psychology must be universal. The idea of evolutionary psychologists has been that human psychology is so complex that it must involve many genes. According to this logic, different adaptive strategies in different people would require the inheritance of many different alleles at many different loci. Sexual reproduction with recombination makes the coinheritance of particular combinations of alleles at different loci very unlikely. Thus, complex psychological adaptations could not be polymorphic in human populations, and human psychology must therefore be universal.

Buller begins by noting that this argument would make sex itself impossible. Sexually dimorphic characters depend on a complex set of genes. But the expression and regulation of these genes is accomplished by a single genetic switch (the SRY gene) which is inherited as a single allele. Thus, the existence of such genetic switches provides an alternative explanation for the occurrence of multiple psychological strategies in a population.

Tooby and Cosmides hope to forestall this line of ragument, however, on the grounds that genetic switches are very rare in nature. They argue that selection consistently favors adaptive plasticity over polymorphic genetic switches as a method of producing adaptive differences (Buller 2005:116).

To shut down this argument, Buller again turns to sex. In mammals, sex is a genetic switch. In crocodiles, it is determined by incubation temperature. Some fishes alter sex in accordance with the prevailing sex ratio. There is no reason to think that any one of these methods is generally preferred in nature; each addressed adaptive proboems in the ancestors of the extant groups. Buller notes that frequency-dependent selection is just as effective on simple genetic switches as adaptive plasticity could be, even in principle.

On the other hand,

...there are some circumstances to which systems of adaptive plasticity are better adapted than genetic switches. In particular, when the environment is rapidly changing and unpredictable, the flexibility provided by phenotypic plasticity will clearly be a greater asset to an organism than a genetic switch. That is, if the environmental features being adapted to are highly variable from one generation to another, so that the phenotype determined by a particular form of a genetic switch would be effective at some times but not others, then phenotypic plasticity, which can produce phenotypes that are adaptive in each of hte variant environments, will clearly be more effective than a genetic switch (Buller 2005:118, emphasis in original).

The conclusion is that sometimes adaptive plasticity may be adaptive, and other times genetic switches may be adaptive, and there is no general rule. This means that there is no reason to believe that the evolved aspects of human psychology should be invariant or universal.

At the end of the chapter Buller engages in a reductio ad absurdum concerning "developmental programs". The "developmental program" has been proposed as the form of the "universal" aspects of human psychology. Since humans clearly have psychological differences, the developmental program is proposed as a set of if-then rules that construct minds in accordance with environmental inputs.

The essence of Buller's argument is that at least some of the time, some ancient human groups must have faced novel environments in which the developmental program had no preexisting instructions to create adaptive psychological mechanisms. Even so, many such people must have survived and managed to develop in adaptive ways. But if some people managed to adapt effectively to novel environments, there is no reason to think that all people couldn't have done so. This obviates the need for a universal "developmental program" entirely: if humans just have brains that are able to develop in adaptive ways in different environments, this solves the problem without the need for an additional level of specification:

But if adaptive phenotypes can develop in some environments without the need for a rule, they can develop in all environments without the need for a rule. This means that the notion of a set of rules embodied in a developmental program guiding development is idle; it plays no genuine role in explaining how development occurs. When we develop differently, it is not because something that is the same in us simply responds differently in a programmed way to differences outside us (Buller 2005:125, emphasis in original).

More on Adapting Minds


Buller DJ. 2005. Adapting Minds : Evolutionary Psychology and the Persistent Quest for Human Nature. Bradford Books, New York. Amazon

Lewontin RC. 1983. The organism as the subject and object of evolution. Scientia 118:65-82.