A considerable proportion of the mean differences in body size among the populations we have been examining is due to the effects of environmental conditions. Some of the differences between individuals within populations are also due to differences in environment. In the better-off populations of industrialized countries these latter differences are relatively small, while in the developing countries the gap between well-off and poor is greater. A child may receive numerous insults during growth and yet survive, but bodily adaptations for survival are made which may result in a slower tempo of growth and a smaller body size. If a whole population receives similar insults, such as a diet low in calories or protein, a small mean adult size results. If environmental conditions improve, the size both of children and adults increases. ‘Human height’ wrote Louis-Rene Villermé, the founder of public health in France, ‘becomes greater and growth takes place more rapidly, other things being equal, in proportion as the country is richer, comfort more general, houses, clothes and nourishment better and labour, fatigue and privation during infancy and youth less; in other words, the circumstances which accompany poverty delay the age at which complete stature is reached and stunt adult height’ (1829, cited in Tanner, 1981, p. 162).

There are many environmental factors which affect growth, and which combine in various proportions to constitute the environment of poverty; but in the final analysis most of them hinge upon the level of nutrition in conjunction with the prevalence of childhood infection.