Test of socioeconomic causation of secular trend: stature changes among favored and oppressed South Africans are parallel.

Secular trends in body height, however common, run at different rates and even in opposite directions in various populations. The standard explanation is that direction and tempo of the trend are reflections of changes in the socioeconomic situation. The aim of this work is to test this hypothesis by examining trends in different socioeconomic groups living in the same country. Our observations on affluent South Africans of European extraction (AE) and on Polish medical students are compared with the data on statures of other affluent and poor peoples from the two countries measured at various dates during the 19th and 20th centuries. The trend among native Southern Africans is erratic (Tobias: South African Journal of Medical Science 40:145-164, 1975), but the overall direction is positive with a slow rate (0.24 cm/decade for 72 Negroid male groups and 0.48 cm/d for 28 Khoisan male samples). Magnitude of the trend among adult AE (0.41 cm/d for females, 0.59 for males) does not differ significantly from that among natives. The trend was absent in the data for 10-year-old AE boys and girls. The rate of trend among AE is much lower than that in their countries of origin (mainly Holland and Britain). The trend among AE medical students is markedly weaker than the trend among Polish medical students (1.21 cm/d), who in turn parallel Polish general conscripts (1.24 cm/d). It follows that the explanation of the secular trend as being an ecosensitive response of individuals to changing levels of well-being is insufficient.