In complete contrast to social learning theory, the evolutionary view point (Symons, 1979; Wilson, 1981a) is that those selective forces responsible for producing the differing physical stature and reproductive equipment of men and women are capable of producing differences in male and female brains as well. Furthermore, there would be definite advantages in doing so. Such brain differences would manifest themselves in instincts and emotions, fantasies and desires, preferences and motives, leading to behaviour that would serve the interests of the individual and ultimately ensure the survival of his or her genes into the next generation. In this connection it is important to realize that the interests of male and female animals are not always the same. Distinctive strategies of behaviour can be seen to serve the reproductive effectiveness of males and females respectively.

This general viewpoint is sometimes called the ‘selfish gene’ or socio-biological approach to understanding animal behaviour. The underlying assumption is that our bodies and brains are merely transient machines geared to the preservation and proliferation of our genes. In other words, genes are the units to be considered in the struggle for survival – not the animals themselves or ‘the good of the species.’ Most modern biologists are coming around to accepting this point of view.

Suppose that male animals have become specialized as hunters and females as child-rearers, what differences would we expect to see? First, we would expect a number of physical differences: males would be faster and stronger and geared particularly to short-term performance. Their muscular bodies would be well equipped for brief bursts of energy, but their metabolism would render them more susceptible to heart disease. Females would be constructed with broader hips for childbirth (though disadvantageous for running) and a built-in food supply for the infant (breasts). A body geared to endurance under conditions of environmental privation (e.g. one storing energy reserves in the form of fat deposits) would be appropriate to females rather than one designed for short-term energy expenditure.

Secondly, we would expect to observe a number of mental and emotional differences supporting this general specialization of function (see Table, from Symons, 1979; Seward and Seward, 1980; Ellis, 1986). Males would be more brave and ruthless, so as to be more effective in battle and defence against marauders. They might also develop high-level spatial intelligence that would help them explore the environment, wield weapons and throw projectiles accurately. At the same time, females would be expected to develop the qualities of protectiveness, nurturance and loyalty that would support their mother role, together with a concern for security that would manifest itself as anxiety or fear in threatening environments. In advanced mammals we might also expect the females to develop special communication skills, so that cultural experience could be transmitted effectively to the offspring. Verbal fluency and social intuition would be obvious human examples of such interpersonal skills.

Since individuals who displayed these attributes would perform their sex role more successfully, their genes would have superior survival value, and so we would expect progressive differentiation of physical and mental equipment as parallel evolutionary developments. If men and women did not show biologically based differences of the kind described, evolutionary theorists would wonder why not. In fact, these very differences are the ones that are observed, fairly universally, regardless of species or culture, time or place.