In all recorded populations, women are on average shorter than men; in a survey of European, Asian, African and American populations reported by Stini (1975: 125), for example, the range in the ratio of male to female adult mean stature was 1.046 to 1.090. A number of human biologists and physical anthropologists have attempted to explain this inter-population sexual dimorphism in stature: cultural and environmental influences do not appear to explain much of the variation in sex differences, and it is suggested that the inter population variation in sex difference has a strong genetic component (Eveleth, 1975; Gray and Wolfe, 1980). Inter-population variation in sex differences in mean stature by social class, and changes in the ratio of male to female adult mean stature for the same population over time, however, are attributed to environmental influences. It is suggested that, because of the female's greater investment in reproduction to support pregnancy and lactation, girls are more protected than boys against the effects of malnutrition and disease during the period of growth. Being more influenced by the effects of the environment, males show greater response to the removal of environmental stress. lt follows that the ratio of male to female mean height should be higher for the better off social classes who are more nutritionally secure and less exposed to disease.

Similarly, as nutrition improves and morbidity is reduced over time, the ratio of male to female mean height should increase pari passu with the increase in the mean height of the population (Eveleth and Tanner, 1990: 200; Bielicki, 1986, Vol. 3: 298; Stinson, 1985: 123; Tobias, 1972:98-101). The ratio of male to female mean height becomes, in effect, an indicator of environmental betterment though Tobias (1972. 101) is careful to add a caveat: it does not necessarily follow that in populations which are well nourished and suffer relatively low levels of morbidity, further betterment in environmental conditions will have the same effect on sexual dimorphism in stature as in extremely deficient populations. And Kuh, Power and Rogers (1991) document that in 20th century western countries this relationship between environmental improvement and changes in the sexual dimorphism in stature is not well defined.