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Key Words hominin, climate, nutrition, growth, adaptation
* Abstract 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.
INTRODUCTION
Body size and shape vary considerably among living human populations. Mean body mass (weight) varies by 50% or more, within sex, in a worldwide sampling of populations (Ruff 1994), even if Pygmies are not considered. Mean body height (stature) and breadth (bi-iliac or maximum pelvic breadth) also vary between the same samples, although in different ways. Variation in height is smaller (about 10%) and does not follow any particular geographic trend. Variation in breadth is larger (about 25%) and shows a clear latitudinal gradient. The explanation for this difference, and some other systematic human body shape differences, may lie in basic physiological adaptive mechanisms, as discussed below.
There is abundant evidence that both body size and shape were even more variable among Plio-Pleistocene hominins (e.g., Jungers 1988, Ruff 1991, Aiello 1992, McHenry 1992) and, within geographically dispersed taxa, followed clines that were similar to those found among modern humans (Trinkaus 1981; Ruff & Walker 1993; Ruff 1994; Holliday 1997a,b). General temporal trends in body size are also apparent in the fossil record (e.g., Ruff et al. 1997). An appreciation of such variation among human ancestors is important for several reasons: (a) Body size (and within-taxon variation in body size) is related to many other characteristics of a species, including life history parameters, ecology,...