Human Nature and the Limits of Science, by John Dupré (Oxford: Clarendon Press, 2001).

ISBN 0-19-924806-0

This book is an extended attack on the pretensions of evolutionary psychology to delineate our human nature and to explain our behavior. It also contains a subsidiary attack on the similar pretensions of rational choice theory and classical economics; and in a final chapter it defends an account of free will. In this review I shall only comment directly on the chapters which relate to what I know best (namely, evolutionary psychology), and which occupy the main body of the book. Readers can draw their own inferences concerning the likely value of the remainder: simple induction suggests that it is of equally poor quality. I shall, however, leave this for experts in the relevant fields to decide.

My view is that Dupré makes a fundamental mistake at the outset, concerning the difference between the sociobiology movement which flourished in the 1960s and 70s, on the one hand, and the evolutionary psychology program pursued by a wide range of researchers over the last two decades, on the other. For he treats the difference as being one of mere name only (p.2). In fact, however, the distinction between sociobiology and evolutionary psychology is as fundamental as that between behaviorist and cognitivist psychology, and for essentially the same reasons. I shall elaborate on this point in the paragraphs which follow.

(Admittedly, Dupré does later acknowledge that there is one distinctive fact about evolutionary psychologists - namely, that they are apt to couch their views in terms of evolved modules (p.22). But he plainly thinks of these modules as systems which are there to guide specific types of behavior. In which case it would be true that we only have a notational variant on the sociobiologist’s picture of evolved behaviors and behavioral tendencies - the only real difference would be that evolutionary psychology postulates specific brain-mechanisms for the behaviors in question.)

Sociobiology was grounded in the behaviorist assumptions which dominated both philosophy and psychology throughout the middle part of the 20^th Century, following the work of Ryle (1949), Watson (1924) and Skinner (1957). The difference is just that, whereas behaviorism tended to place a heavy emphasis on learning, sociobiologists began to speculate that many behaviors and behavioral tendencies might be more directly biological in origin. Evolutionary psychologists, in contrast, have fully embraced the cognitive revolution in psychology and philosophy which began (legend has it) with Chomsky’s (1959) review of Skinner’s Verbal Behavior, and which then gathered increasing momentum through the later decades of the century.

Sociobiologists such as Wilson (1975) argued that evolution should have shaped the behaviors and behavioral tendencies of human beings, in just the same way that ethology was revealing how evolution had shaped the behaviors of other animals; and they then set out to provide evidence for such a contention. They recognized, of course, that any innate behavioral tendency would need to be realized in a brain mechanism of one sort or another. But their view was that such mechanisms would be selected for because of their role in mediating between input releasing-conditions, on the one hand, and behavior, on the other. For in the end, it is the behaviors of organisms which have an especially large impact on the chances of survival and reproductive success of those organisms, so it is behaviors and behavioral tendencies which would be selected for. Sociobiologists could go at least some way towards explaining the distinctive flexibility of human behavior, however, since behavioral tendencies can have many and various releasing conditions. Nevertheless, numerous people have thought it to be a valid criticism of sociobiology that human behavior is just too flexible to admit of direct evolutionary explanation, except in rare cases. This point is reiterated by Dupré, often and at length.

Evolutionary psychology, in contrast - as heir to the cognitivist revolution - takes quite seriously a belief / desire (or an information / goal) organization of psychological systems. This is true even in the case of insects, where it turns out that the desert ant has states representing that a food source is 44.64 meters North-East of its nest on a bearing of 16.5 degrees, say, which it can deploy either in the service of the goal of carrying a piece of food in a straight line back to the nest, or in returning directly to the source once again - or, in the case of bees, when the goal is to inform other bees of the location of the food source (Gallistel, 1990, 2000). What has been selected for in the first instance, on this view, are systems for generating beliefs and desires; the behaviors which result from those beliefs and desires can be many and various. Indeed, once modules for gathering information about social norms, and for generating desires for things which will enhance social status, say, are factored into the evolutionary psychology equation, then there seems no limit to the flexibility of behavior which an evolved modular psychology could issue in.

There might seem to be a paradox inherent in the evolutionary psychology position here, however. For if it is behavior which ultimately influences the survival and reproductive success of individuals - as everyone acknowledges - then how could it not be behaviors and behavioral tendencies which are selected for in evolution, just as sociobiologists suppose? Yet the apparent paradox is easily resolved within the framework of belief / desire psychology. For mechanisms which generate reliable information / true beliefs will make fitness-enhancing behaviors more likely, provided that the organism’s goals are for things which would enhance fitness; and vice versa for the mechanisms which generate such desires, on the assumption of reliable information. The point is just that the same item of information (e.g. the compass bearing of a food source) can be deployed in the service of a number of different goals; in which case mutations which enhance the reliability of that information, or the speed with which it is acquired, are likely to have a positive impact on a whole variety of fitness-enhancing behaviors. Similarly, a given goal can often be approached in a number of distinct ways, subserved by a variety of different beliefs about the means to realize that goal; so mutations which make beneficial adjustments in goals are likely to manifest themselves in a range fitness-promoting behaviors, too.

Largely because he doesn’t really distinguish between evolutionary psychology and the earlier sociobiology movement, Dupré alleges that evolutionary psychologists will have difficulty in explaining the manifest diversity of human behaviors and human cultures (p.16). And he himself is at pains to emphasize - in alleged contrast to evolutionary psychology - that human brains and human minds develop in interaction with culture, where cultures differ from one another in many significant ways (pp. 31, 37, 100). But no evolutionary psychologist would disagree with the latter point. On the contrary, they have seen part of their task from the outset to be that of explaining how evolved psychologies both constrain and are shaped by cultures (Barkow et al., 1992). And as I pointed out above, once an evolved psychology with a belief / desire architecture has mechanisms for generating beliefs about norms, and mechanisms for generating social goals (such as desires for certain kinds of norm-compliance, for social status, and such like) then we shall begin to see patterns within cultural diversity, as well as to understand its underlying basis.

According to Dupré, too, evolutionary psychologists are supposed to minimize the role of learning in development, and in explaining our mature capacities and behaviors (p.29). Nothing could be further from the truth. The various psychological modules postulated by evolutionary psychology are, almost all of them, learning mechanisms of one sort or another. Once the commitment of evolutionary psychologists to belief / desire cognitive architectures is fully appreciated, indeed, it becomes obvious that the modular systems in question are learning systems. (At least, this is so in connection with belief-generation; I shall return to the case of desires in a moment.) The system in the ant which uses dead reckoning to figure out the exact distance and direction of a food-source in relation to the nest (given the time of day and the position of the sun) is a system for learning that relationship, or for acquiring a belief concerning that relationship. Similarly, the language system in humans is, in early childhood, designed for learning the syntax and vocabulary of the surrounding language; and in older children and adults it is used to learn what someone has just said on a given occasion, extracting this information from patterns in ambient sound.

Desires aren’t learned in any normal sense of the term ‘learning’, of course. Yet much of evolutionary psychology is concerned with the genesis of human motivational states. This is an area where we need to construct a new concept, in fact - the desiderative equivalent of learning. Learning (as normally understood) is a process which issues in true beliefs, or beliefs which are close enough to the truth to support (or at least not to hinder) individual fitness. But desires, too, need to be formed in ways which will support (or not hinder) individual fitness. Some desires are instrumental ones, of course, being derived from ultimate goals together with beliefs about the means which would be sufficient for realizing those goals. But it is hardly very plausible that all acquired desires are formed in this way.

Theorists such as Dupré are apt to talk vaguely about the influence of surrounding culture, at this point. Somehow desires such as the desire to approach a particular woman on a particular occasion, or an older man’s desire to be seen in the company of a beautiful young girl, are supposed to be caused by cultural influences of one sort or another – prevailing attitudes to women, perceived power structures, media images, and so forth. But it is left entirely unclear what the mechanism of such influences is supposed to be. How do facts about culture generate new desires? We are not told.

In contrast, evolutionary psychology postulates a rich network of systems for generating new desires in the light of input from the environment and background beliefs. Many of these desires will be ‘ultimate’, in the sense that they haven’t been produced by reasoning backwards from the means sufficient to fulfill some other desire. But they will still have been produced by inferences taking place in systems dedicated to creating desires of that sort. A desire to have sex with a specific person in a particular context, for example, won’t (of course) have been produced by reasoning that such an act is likely to fulfill some sort of evolutionary goal of producing many healthy descendants. Rather, it will have been generated by some system (a module) which has evolved for the purpose, which takes as input a variety of kinds of perceptual and non-perceptual information, and then generates, when appropriate, a desire of some given strength. (Whether that desire is then acted upon, will of course depend upon the other desires which the subject possesses at the time, and on their relevant beliefs.)

The issue is not, then, the extent to which learning is involved in the causation of human behaviors. Both evolutionary psychologists and their opponents can agree that learning is ubiquitous. Nor is the issue even whether the algorithms used in learning are domain-general (being suitable for extracting many different kinds of information), or are rather specific to a particular domain. (Though the domain-specificity of learning algorithms is certainly an interesting question.) It is rather whether the various mechanisms which engage in learning have been specifically designed by evolution to extract information, or to generate fitness enhancing goals, within one given domain rather than another.

The main overall theme of Dupré’s book is to mount an attack upon scientism, in fact, defined as ‘an exaggerated and often distorted conception of what science can be expected to do or explain for us’ (p.1). Both evolutionary psychology and many applications of classical economics are said to fall into this general category. And scientism is supposed to go along with some sort of tacit commitment to physicalist reductionism, together with an attempt to explain everything in terms of mechanistic models (pp. 6-7). Of course it is a truism that scientism, so explained, is a bad thing. The question is whether evolutionary psychology (and rational choice theory and classical economics - again I shall limit my discussion to what I know best) really does have the alleged vices.

Once the cognitivist character of evolutionary psychology is seen in clear focus, it should be plain that it is neither reductionist nor mechanistic in character. Explanation of human behavior in terms of beliefs and goals is neither reduced nor replaced. Rather, we have some proposed systems which are said to have been designed to generate reliable information and fitness-promoting goals, together with a research program which is geared towards finding further systems of these sorts. And we have the beginnings of attempts to understand the computational principles on which such systems might operate. This may be reductive explanation, for sure, in the benign sense of seeking to understand the operations of complex systems in terms of the nature and interactions of their parts. But it is not physicalist reduction in the sense Dupré understands; nor (since many of the systems in question are learning systems, as we have seen) is it inconsistent with giving due weight to the environment in explanations of human beliefs, motivations, and behaviors.

Throughout the book, Dupré writes with an annoying sort of sneering tone, jeering at the intelligence and motives of his opponents. Although intended to be witty (Dupré’s cover blurb describes it as such), this will surely prove irritating to anyone not already as convinced as Dupré is of the utter hopelessness of evolutionary psychology and classical economics as viable scientific enterprises. And throughout the book, too, Dupré’s use of sources is highly selective. To the extent that this book has been researched at all, the author seems to have trawled the literature for just long enough to find a study which he can then see some way of mocking. This is a great pity, since Dupré does have some interesting things to say, about the so-called ‘unity of science’ for example. Would that his scholarship had been better, and that he had not been so enamored of his own rhetoric! In conclusion, I can only suggest that the Oxford editor should review his or her standards for refereeing monographs.

PETER CARRUTHERS

University of Maryland, College Park

References

Barkow, J., Cosmides, L. and Tooby, J., eds. (1992). The Adapted Mind. Oxford University Press.

Chomsky, N. (1959). Review of Verbal Behavior by B.F. Skinner. Language, 35.

Gallistel, R. (1990). The Organization of Learning. MIT Press.

Gallistel, R. (2000). The replacement of general-purpose learning models with adaptively specialized learning modules. In M. Gazzaniga (ed.), The New Cognitive Neurosciences (2^nd Edition). MIT Press.

Ryle, G. (1949). The Concept of Mind. Hutchinson.

Skinner, B. (1957). Verbal Behavior. Appleton Century Crofts.

Watson, J. (1924). Behaviorism. Norton and Company.

Wilson, E.O. (1975). Sociobiology. Harvard University Press.