The evolution of body size and shape in the human career

Abstract

One contribution of 17 to a discussion meeting issue 'Major transitions in human evolution'. Body size is a fundamental biological property of organisms, and documenting body size variation in hominin evolution is an important goal of palaeoanthropology. Estimating body mass appears deceptively simple but is laden with theoretical and pragmatic assumptions about best predictors and the most appropriate reference samples. Modern human training samples with known masses are arguably the 'best' for estimating size in early bipedal hominins such as the australopiths and all members of the genus Homo, but it is not clear if they are the most appropriate priors for reconstructing the size of the earliest putative hominins such as Orrorin and Ardipithecus. The trajectory of body size evolution in the early part of the human career is reviewed here and found to be complex and nonlinear. Australopith body size varies enormously across both space and time. The pre-erectus early Homo fossil record from Africa is poor and dominated by relatively small-bodied individuals, implying that the emergence of the genus Homo is probably not linked to an increase in body size or unprecedented increases in size variation. Body size differences alone cannot explain the observed variation in hominin body shape, especially when examined in the context of small fossil hominins and pygmy modern humans.This article is part of the themed issue 'Major transitions in human evolution'.

Mosaic evolution and the pattern of transitions in the hominin lineage

“…No matter how great an impact such a brain size increase is, it is still a small rate of change, and would qualify as baseline evolution. Grabowski et al's [38] recent presentation of body size changes across the hominin range also illustrates what must be simple baseline-but not unidirectional-change in body size [39]. The problem with most examinations of changes in broad parameters such as brain size and body size is that they are often not lineage specific (e.g.…”

Pleistocene Hominin Fossil Femora and Humeri

“…A recent study [19] preferred pygmy standards for estimating stature of the Plio-Pleistocene australopithecines using a formula: Stature (cm) = [0.331 x femur length (mm)] + 15.876; R= 0.89, s e e= 3.7. However, they yielded very low of statures (around 100 cm) for the Narmada hominins which sounds unrealistic, and may not hold good for such later Middle to Late Pleistocene hominins.…”

Major transitions in human evolution

“…Antó n et al [9] show that H. erectus is highly variable, not just in body size (see [3]), but also in other aspects of its morphology. The appearance of modern humans is seen at about 195 Ka at Omo Kibish in Ethiopia (figure 3), but Stringer [10] argues that the lineage leading to it shows derived traits earlier than this, and so the transition is spread over several hundred thousand years, and that it is likely archaic populations persisted across the African continent, some until into the late Pleistocene [11].…”

“…Jungers et al [3], for example, consider body size across all hominins and show that the early bipedal ape versus the human-like hominins divide does not exist; they show overlapping patterns, and certainly no contrast between the two at a point of 'origins'. The idea that the emergence of Homo is associated with an increase in body size is not supported.…”

“…(2) Does the pattern of change fit a model of short transformations, or gradual evolution? (3) Why is the role of Africa so prominent? (4) How are different aspects of adaptation-genes, phenotypes and behaviour-integrated across the transitions?…”