|
pubmed:otherAbstract |
PIP: It is suggested in this discussion that the secular trend in maturation is best viewed as an aspect of the demographic transition in mortality, which in turn can be ascribed to improvements in medical care, hygiene, sanitation, workload and to possible improvement in nutrition. Both increase in energy input and reduction in the demands of maintenance most likely contribute to more rapid growth and maturation. The infant mortality rate is used as a relatively sensitive index of the morbidity and mortality experience of a population. Variation in this parameter is compared with variation in mean menarcheal age or mean age at the peak of the adolescent growth spurt in girls as an index of maturation rate. The relationships between these parameters both within populations over time and between contemporaneous populations are of interest. A persistent result in mathematical treatments of life history theory over time indicates that an acceleration of reproductive maturation is an adaptive response to reductions in reproductive mortality. This relationship is exhibited by human populations to a notable degree, possibly as much because of the energetic costs of high morbidity environments as to variation in energy supply. It is difficult to locate evidence bearing on such a causal distinction. Notable, however, is the fact that although children and adolescents have become taller and heavier for their age over the course of the secular trend, their weight for height has actually declined. This fact is well illustrated by Swedish data and is consistent with the observations that weight at menarche has remained fairly constant over the course of the secular trend while height at menarche has increased. The demographic transition and the secular trend may be 2 aspects of a single revolution in human biology, a revolution that is reflected in a changing distribution of energy expenditure.
|
