Auxology is the study of growth and development. The classical interest of biological anthropologists in the comparative anatomy of human groups is represented in many respects by contemporary anthropometric studies. Growth performance in children is a sensitive index of influences of infectious or congenital disease, nutrition, levels of physical activity, and to some degree mental development. As such, the measurement of growth in height, weight and body composition has been an important means of rating the general physical well-being of populations. Growth performance has been known to mirror social economic inequalities since the mid-nineteenth century (Tanner 1988), and has therefore become a means of identifying vulnerable groups, and of monitoring and evaluating the physical correlates of welfare policies. The development of growth references as yardsticks for measuring growth performance has relied primarily on longitudinal or semilongitudinal studies over extended periods.
These have been made on ostensibly healthy Caucasian children resident in Europe or North America and have been recommended by the World Health Organization for general use. It has been argued that differences in linear growth performance between reference populations and healthy, well-off study populations tend to be small compared to differences between rich and poor groups within a given study population. If this were true, then there would be a strong case for using a single universal growth reference. However, patterns of growth in height and weight during childhood in healthy study populations do not seem to follow a constant relationship to reference patterns. It has therefore also been argued that there are ethnic differences in genetic growth potential, or in growth pattern appropriate to the local ecology, which may justify the development and use of locally specific references. Universal references may be valuable as a yardstick for the general comparison of groups, locally specific references for the screening of individuals for a particular purpose.
Linear growth is closely associated with rate of maturation, which is in turn related to changes in body composition (relative fatness) and differs according to sex. The nature of this relationship can only be investigated fully in longitudinal studies, such as that conducted at the Fels Institute in America since 1929. Populations in which children show low stature at any given age tend also to be slow to mature and to reach puberty comparatively late. High median ages at menarche of over 18 years have been recorded in Papua New Guinea. However there is no simple relationship between growth performance, reproductive function, and the demographic structure and dynamics of populations. It has been speculated that body fatness itself influences reproductive function, and therefore provides a link between energy balance and reproductive performance. However, this is probably related to one of various stressors of which the effects are mediated by endocrinological mechanisms which are poorly understood.