Much of sociology today is concerned with the study of inequalities, of which inequality between the sexes is one aspect. I wish to argue the case that the study of sexual inequality has thrown up ideas which help in the understanding of all kinds of structured inequality as well as that between men and women. Briefly, my case is that four key factors can be used to understand woman's position in society, and that three of them are necessary to the analysis of social stratification in general. The three common factors are scale, density of population and level of technology, but I will begin with the consideration of the factor peculiar to the analysis of sexual inequality, the impact on social structure of the fact of infantile dependence. The biological evolution of the human species has been towards greater intelligence and correlative loss of innately patterned behaviour. The human infant has an enormous capacity for learning, but while learning, an enormous dependence on adults for survival and training. Such an evolution of intelligence must have been matched by an evolution of strong drives to nurture and train the young, otherwise the substitution of learning capacity for programmed behaviour would have had no survival advantages, rather the reverse. It seems reasonable to suppose that the innate caring response of adult to young would evolve, together with intelligence, in both sexes equally, and that it would be triggered off in each individual's life by the presence of dependent infants, and be shaped, reinforced and particularized by interaction with particular dependent infants. Given the physiology of reproduction, this nurturant response is likely to be most strongly evoked and reinforced in the biological mother, who through pregnancy, childbirth and suckling, must be most open to the signals of the infant for food, love and care. Therefore it is not contradictory to my hypothesis of equal endowment of the sexes with the capacity and desire to nurture the young that, in fact, in every society the main work of child-care has devolved on the women. But a problem is raised when we realize that child-care has been mostly women's work not just as a matter of practice and convenience, but as a matter of social morality. Not only is women's care of young children morally approved of, but men's participation in such tasks is frequently derided, if not actually tabooed. Yet it follows from my assumption of a poten-