Evolutionary trends in human body form provide important context for interpreting variation among modern populations. Average body mass in living humans is smaller than it was during most of the Pleistocene, possibly owing to technological improvements during the past 50,000 years that no longer favored large body size. Sexual dimorphism in body size reached modern levels at least 150,000 years ago and probably earlier. Geographic variation in both body size and shape in earlier humans paralleled latitudinal clines observed today. Climatic adaptation is the most likely primary cause for these gradients, overlain in more recent populations by nutritional effects on growth. Thus, to distinguish growth disturbances, it is necessary to partition out the (presumably genetic) long-term differences in body form between populations that have resulted from climatic selection. An example is given from a study of Inupiat children, using a new index of body shape to assess relative body mass.
