Some support for the functionalist/traditionalist account of the 'naturalness' and inevitability of sex roles is provided by contemporary sociobiology.
Originally, evolutionary thought was preoccupied by physical rather than behavioural evolution. Now, however, there is a vast literature and evolutionary considerations have been shown to be relevant to understanding behaviour. There has been a revival of authentic Darwinism.
It is particularly with regard to sex that evolutionary considerations suggest that our behaviour must have evolved, and must have been deeply influenced by selection.
If selection selects primarily and ultimately for reproductive success, then sexual behaviour must be particularly relevant to it, since sex and reproductive success are so closely allied.
It seems unlikely that any aspect of behaviour bearing on ultimate reproductive success could have escaped the influence of selective forces and remained at the more or less arbitrary disposal of environmental conditioning as some sociological and psychological approaches have suggested.
Modern insights on the nature of natural selection predicts that behaviour connected to reproductive success will be strongly influenced by evolution, and sexual behaviour is most unlikely to be the result of chance.
Darwin's insight into natural selection was that it was a process of differentiated reproductive success of individuals, acting as individuals.
Clearly, there is a basis for the universal distinction made by human beings between males and females. Sex is not arbitrary, in most cases in modern biology it can be unambiguously defined.
The sex cells produced by men and women are diametrically different. The largest cell in the body is the ovum, the smallest is the sperm. This mirrors the investment made by the parents of a child. Women have a larger parental investment in their offspring. We can define this parental investment as any benefit to an offspring's reproductive success at a cost to the remainder of a parents reproductive success.
Males are potentially able to engender many more offspring than women. Males also however show the greatest variance in reproductive success.
An important factor in the degree of parental investment made by a man will be the mating strategy. In a multi-female system (polygyny), men invest more in mating success than in the parental care of offspring. This strategy produces the greatest variance in male reproductive success. Some males might not have any children. The majority of human societies are either generally polygynous or allow polygyny to the powerful or wealthy.
Polygyny is 'the' mating strategy of our species. The real extent of polygyny is hidden by a male-stream bias, counting the men polygynously married, rather than the women, for example, for every man in such an arrangement there are at least two women.
In uni-female systems, the male investment is less in mating success and more in rearing offspring. This signifies a coming together of male and female roles. Polyandry, one woman and several male partners is found only where males are very poor and normally the men will be brothers.
For females, there is a greater level of parental investment, and, in our species, has an extreme form of sex role specialisation. Females bear the greater cost of child rearing, and, given this, females are selective both about embryos and their subsequent development.
For Example, when age is held constant, mothers with existing offspring have twice the rate of spontaneous abortion as compared with women pregnant for the first time. Sixty percent of miscarriages show some abnormality. There is also a discrimination against the male foetus; 78% of all spontaneous abortions are of males.
Reproductive success is also associated with being married, confidence of paternity, coming from a large family, better mental health, all of which reflect a better chance of parental investment being worthwhile.
Even 'baby-blues' has been tied into assessing the risk of investment - can this child survive a period of relative neglect? Is it worth bothering to invest in it?
Sociologists flinch from sociobiology and argue that humans are different from other animals, the basis of the argument being that only humans have culture. However, it has been argued that some other animals (principally primates) do have culture.
Another reason for the reluctance of sociologists to accept sociobiological views of human behaviour might be due to the differing emphasis of biologists and sociologists.
The social scientist pays attention to differences; the vast differences between human cultures, and that the mechanism that underlies these differences is learning. Social scientists are impressed by the flexibility of humans. Biologists seek uniformity. Compared to other species, humans are remarkably homogenous.
It is probably mistaken to take any particular viewpoint as providing the 'truth'. Our behaviour is unlikely to be exclusively a product of either biology or culture, nor may these phenomena necessarily be easily separated. Culture is one of our most important biological adaptations.
The strongest evidence for the legitimacy of sociobiology may well be the documentation of cross-cultural behavioural universals. A difficulty, however, in the sociobiology of humans, is cultural lag. The cultural framework of modern western society represents the human condition during less than 1% of human history.
Students of animals must constantly be aware of anthropomorphism, the attribution of human behaviour to animals. Similarly, biologically-orientated researchers of human behaviour must be aware of zoomorphism, the attribution of animal motivation to the behaviour of humans, or more likely, the claim that animal and human motivations are the same.
Some people believe that the capacity for self-awareness has liberated humans from the influence of natural selection. Yet consciousness may have evolved as a fitness-maximising characteristic. A further argument (Barash, 1979) is that our consciousness is the core of our self-interest that we try to hide from others.
Sociobiology has been accused of all manners of nastiness; it is a controversial discipline. Yet most sociobiology is concerned with non-human animals, it is the 5% that deals with humans that generates the vast majority of the controversies. The arguments usually revolve around the political and social implications, rather than the discipline itself.
Racism: No theory or data have ever been proposed by sociobiologists purporting to demonstrate racial superiority of any group in any manner. In fact, sociobiology may well provide ammunition against racism, since it deals with biological universals that appear to underlie superficial cultural (and racial) differences.
Sexism: Some of sociobiology's most impressive theory and data involve male-female differences. Sexism seems more useful in describing the differential valuing of one sex over another. The claim that one sex is 'better' than the other would be an evolutionary absurdity.
The Naturalistic Fallacy: This is the old 'is/ought' problem. To try to understand the natural world is not to condone it. What is biological is not necessarily good. Good is a social definition, an assessment of value.
Conservatism: Sociobiologists try to explain, not justify human behaviour. Yet, to repeat, biology and good are not the same.
Social Darwinism: Essentially, social Darwinism was a misunderstanding of evolution. Because it was seen as natural, it was equated with 'good'. But we cannot, logically derive a moral system from a biological process any more than we could from the theory of gravity.
Determinism: It is claimed that sociobiology substitutes determinism for free will. Most theories that attempt to explain human behaviour at a structural level tend to be deterministic in outlook. However, sociobiology is trying to understand our behaviour by observing what we do, not by telling us what we should or have to do.
C. Badcock, 'Evolution and Individual Behaviour', 1991.
D. Barash, 'Sociobiology and Behaviour', 1982.