The cover to an influential collection of essays on evolutionary psychology makes the following confident announcement: With the advent of the cognitive revolution, human nature can finally be defined precisely as the set of universal species-specific information-processing programs that operate beneath the surface of cultural variability; this collection of cognitive programs evolved in the Pleistocene to solve the adaptive problems regularly faced by our hunter-gatherer ancestors such as mate-selection, language acquisition, cooperation, and sexual infidelity. Beneath the business suits, saris, or loincloths of modern humans apparently going about the multifarious business of modern life, we learn, are really cave people seeking out mates or sniffing out one another’s sexual infidelities. It often appears that this covert human nature can be discovered by little more than reflection on the ways that ancestral cave people would have maximised their reproductive success. Whatever the epistemological attractions of this atavistic account of human nature, I shall argue (briefly, for reasons of space) that it is oversimplified and poorly grounded.
We may begin by noting that to the (considerable) extent to which this theorising about human nature is based upon a priori speculation, it must be treated with suspicion. It would be relatively easy to do such a priori biology if organisms could be assumed to be optimally designed for the environments in which they lived, or even once lived. But while it may have been only pious to suppose that organisms were optimally designed when it was assumed that they had been created out of whole cloth by an omniscient and omnipotent designer, without major qualification this supposition has no place in contemporary evolutionary thought. The point is nicely encapsulated in a little anecdote. Two anglers, so the story goes, are fishing for salmon in Alaska. Suddenly one of them sees a polar bear rapidly approaching. He hurriedly removes his waders and begins putting on his sneakers. “You fool,” says his companion, observing this activity and its cause. “You can’t outrun a bear whatever you’re wearing.” “You fool,” says the first, “I don’t have to outrun the bear, I only have to outrun you.” The point of this little episode of natural selection hardly needs elaboration. Survival of the fittest doesn’t mean survival of the fittest possible, just survival of the fittest actual. Thus design analysis of hypothetical ancestral organisms has little significance unless we know a good deal about the range of behaviour actually exhibited by actual ancestors.
It is a familiar and trivial point that whereas our brains surely evolved, much of the behaviour they now allow us to engage in is very different from any that could have served to further their evolution. While our brains were evolving nobody was engaged in the study of quantum mechanics or even shopping at the local supermarket. Clearly our brains do not limit us to those kinds of behaviour that may have served our interests in the Pleistocene. Nevertheless, evolutionary psychologists insist that our brains did evolve in ways that severely constrain our present behaviour, ways that can be greatly illuminated by consideration of the exigencies of life in the Pleistocene. More specifically, it is argued that the brain is divided into many distinct components, or modules, each designed by evolution to perform optimally on a quite specific task. A topic of central interest to evolutionary psychologists is sex, and to illustrate what I take to be some of the general weaknesses of the programme, I shall look at some of their ideas on one aspect of this subject, sexual attractiveness.
It is hardly surprising that sexual behaviour should be a matter of interest to evolutionists. From an evolutionary perspective, reproduction is the most significant thing that organisms do, and until quite recently sex was a necessary condition for human reproduction. Obviously enough, it is of great evolutionary importance to select suitable mating partners. Evolutionary psychologists have proposed a wide range of evolved criteria for human mate selection. Some of these are quite exotic, for example the proposal that men look for an optimal waist-to-hip ratio of about 0.7, a hypothesis that has occasioned much labour poring over Playboy magazines with callipers. Many are banal, for example the absence of open sores or lesions indicative of good health, or kindness and understanding. The central claims, however, are that men are attracted to women with maximum potential fertility – basically the younger the better, and women are attracted to men with the greatest resources for providing for their offspring.
Leaving aside most of the details of this story and a range of more specific worries, two points should be stressed. First, even if our hypothetical cavemen ancestors selected mates solely on the basis of their reproductive potential, things have got a bit more complicated. So-called trophy wives would not, perhaps, be accounted trophies if there were not some recognised virtue to mere youthful good looks; but a trophy wife seriously deficient in intelligence, charm, good manners, etc. would, I suppose, be as often an embarrassment as a prize. Prudent mate-selection, that is to say, involves a wide range of factors, many of which have nothing whatever to do with purely physical attractiveness. Although evolutionary psychologists do mention a range of such factors, the attempts to explain the importance, for example, of intelligence or kindness in terms of effects on fertility are both implausible and redundant.
The second, and perhaps more important, qualification is that mate-selection, in the sense of selection of a long-term partner for the bearing and rearing of children, is hardly the sole context in which modern humans make judgements about the attractiveness of other people. Whether or not this was true of our less sophisticated ancestors, contemporary humans are interested at different times in a variety of different kinds of relationships with members of the opposite sex (or, in many cases, the same sex; though how this relates to the present issue is obviously problematic). They may seek friendship, casual sex, a brief romance, lifelong companionship, a co-parent for their children (existing or yet to be born), a status symbol, a domestic drudge, and so on. Presumably the relevance of prehistoric whisperings concerning reproductive potential will vary considerably from one to another of these cases. This points to a very general problem for the allegedly modular evolved mind. However modular the mind may be, the output of such modules must somehow be integrated into some broader process in which whole human beings come to make decisions, and must be capable of weighing modular outputs differently according to different ends to which the decision-making process may at any time be directed. There must be some part of the mind in which it is possible to decide whether to pursue a potential mate or forage for carrion in McDonald’s. Suppose, for the sake of argument, that there is indeed a mechanism in the human brain that disposes men to select very young women or girls as ideal mates. Given that this atavistic mechanism provides only one of a range of inputs into actual processes of mate-selection, and given that mate-selection, in the sense assumed by evolutionists, is only one of a range of kinds of behaviour in which this hypothetical machinery might figure, it is not at all clear that identifying such machinery will tell us anything much about the behaviour or even behavioural dispositions of modern humans. At the most, we might learn something about psychopathology: the mal adapted mind, the mind unable to function in the conditions in which it finds itself, is perhaps a mind constantly and uncontrollably driven by uninterpreted urges from its evolutionary past. At any rate, whether or not much would follow from the identification of these modules, I want now to look at the processes by which they are, allegedly, disclosed.
Whereas in the early days of sociobiology a priori argument and stereotyped clichés about sexual difference were generally considered sufficient evidence for the evolutionary illumination of human sexuality, recently this has been augmented by a great deal of empirical study. Whether much of this research provides compelling evidence for the hypothesised psychological mechanisms is another matter. In some cases the research involved would most naturally be taken as self-parody, if it were not in fact taken as serious science, published in leading scientific journals. I think, for instance, of the investigation of the hypothesis that rape is an evolved male reproductive strategy by the method of so-called objective phallometry, which involved the exposure of prison inmates to filmed depictions of rapes, with measuring devices attached to their penises. Even discounting the possibly atypical nature of this sample, the inference from sexual arousal by these movies to an innate disposition to rape has all the plausibility of the inference that overweight middle-aged men who show objective signs of excitement when watching football games on Sunday afternoons must have some disposition to play professional football.
Somewhat less absurdly, David Buss has investigated the criteria of mate-selection by sending questionnaires to substantial numbers of people in a variety of cultures asking them to rate the importance of various characteristics for potential mates. He did indeed discover that in most cultures men claim to attach more significance than women to youth and beauty. On the other hand the significance of chastity, which evolutionary psychologists predict should be of great importance to men but much less to women, was found to vary greatly from culture to culture. In China, for example, it was found to be of great and equal importance to both sexes, in Germany or Sweden it was of very little importance to either. Thus Buss concludes that “some preference mechanisms are highly sensitive to cultural, ecological, or mating conditions, while others transcend these differences in context.” It is, of course, equally possible that the social conditions that encourage some of these preferences are currently less variable than those that support others.
The ease with which evolutionary psychologists can accommodate data is even more striking in a paper by Bruce Ellis commenting on the fact that in questionnaires women, contrary to evolutionary prediction, claimed to attach little importance to either dominance or social status. Ellis offers four possible explanations: they may mistakenly have supposed that the men were disposed to dominate them rather than other men; they may be reluctant to admit that they prefer such men; they may prefer such men but be unconscious of the preference; or their assumed reference class may only include high status men, among whom details of status will not be important. Perhaps so. But methodologists will surely see here the stigmata of a research program with a whiff of degeneration – if, indeed, that does not imply more antecedent progressiveness than is evident.
A different experimental methodology involves showing subjects pictures of members of the opposite sex and asking them how attractive they found the persons depicted, or whether they would be willing to engage in various kinds of relationship with them. Such procedures were used, for example, in the investigation of the hypothesis that men were attracted to women with a 0.7 waist-to-hip ratio. Given limited time, however, I shall refrain from commenting on this style of research beyond remarking that an extremely narrow and simplistic conception of attractiveness must be assumed: it is difficult to make reliable judgements from a still photo as to kindness and understanding, or intelligence, for example; still less from a line-drawing, as was the case in the waist-to-hip ratio research.
The empirical research is, then, disappointing. Various hypotheses are suggested for the criteria of human mate-choice or judgements of attractiveness. Many of these are familiar and banal. Sometimes, especially in the banal cases, the hypotheses are to some degree confirmed. This shows that the psychological mechanism is at work. In other cases they are not. This with the help of a range of ready-to-hand auxiliary hypotheses shows that the psychological mechanisms interact with cultural forces. It would not only be grossly premature, but potentially dangerous, to suppose that much had been learned about the innate bases for human mate-choice. I want now to consider some more theoretical worries about the general picture that informs contemporary evolutionary psychology.
I recently read a report on the mapping component of the Human Genome Project, the attempt to assemble maps of the approximately 100,000 genes on the human chromosomes, which noted in passing that “this collection of genes contains the complete instructions about how to make a human body.” Something like this is, I suppose, widely held to be a contemporary truism, and a truism that underlies the assumption that the structure of our brains is more or less determined by features of our chromosomes. Yet far from being a truism, this statement is completely false. A full set of human chromosomes has no chance of producing a human body unless it is situated in a human cell replete with all the proper transcription, energy-processing, etc. cellular machinery; the cell must be properly situated in the right part of a human female body; and the human female must be situated in an adequately sustaining social and ecological environment, etc. It is sometimes supposed that there is a fundamental asymmetry between the genes on the one hand and all these contextual prerequisites on the other. Probably this is most commonly expressed in the idea that the genes carry information for which these various levels of environmental context provide merely a channel. But this is an untenable position. Simply put, there is no sense of information in which the genes carry information that can be read off by the environment in which it cannot equally well be said that the environment carries information which is read off by the genes. More simply still, there are many sources of information that are required in building a human body – genetic, cellular, physiological, and, especially at later stages, cultural. All are necessary, none is sufficient. The atavism inherent in evolutionary psychology is ultimately grounded in the idea that the transmission of human behaviour from generation to generation is essentially based in the transmission of the physical structures of brains through physical structures of genes. And physical structures of genes are taken to be more or less constant over historical time. But there is no reason to assume this simple picture of the transmission of behaviour, and excellent reasons for believing that the reality is far more complex. In the absence of this simplistic genocentric picture, finally, there is no reason to assume that our behaviour is adapted to the conditions of our distant past.
I have so far assumed that it is clear what is at stake in claims about the modularity of mind. But in reality this is anything but clear. No one, I assume, thinks the brain is a wholly amorphous structureless mass, and no one supposes that it is exhaustively divided into wholly independent systems entirely dedicated to particular areas of behaviour. The reality, I think, is that claims about mental modules are claims that fairly specific aspects of behaviour are generated by genetically coded structures in the brain. Although there are now few strict genetic determinists – the causal chain from gene to behaviour is too long and attenuated for such a view to be remotely plausible – specialised evolved mental modules are nevertheless the contemporary vehicle through which somewhat qualified versions of genetic determinism are currently expressed. With arguments for the existence of such mental modules almost exclusively a prioristic, and evidence for the behaviour they are supposed to generate equivocal at the very best, we should treat this school of genetic determinism with all the respect that thinking people have come to accord to its predecessors.
This is an abridged version of Section ii of “Against Reductionist Explanations of Human Behaviour”, published in Proceedings of The Aristotelian Society, Supplementary Volume, LXII, pp. 153-171.