Fossils and the mosaic nature of human evolution

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Science  31 Oct 1975:
Vol. 190, Issue 4213, pp. 425-431
DOI: 10.1126/science.809842


These new fossils, dates, analyses, and interpretations lead to confirmation and refinement of the mosaic scheme of human evolution as proposed by early evolutionists such as Lamarck, Haeckel, and Darwin. Evolutionary changes in the body adapting our ancestors to bipedalism occurred before 3 million years ago, judging by the completeness of the adaptation in the late Pliocene-early Pleistocene hominids. The skeletons of these early hominids were not identical to those of modern humans, but locomotor behavior was probably human. At about 3 million years ago their brains were relatively small, although internal reorganization may have been taking place. By 2 million years ago a wider range of variation in brain size appears in the fossil record, with an average size somewhat larger than that in earlier hominids. Concomitant with this beginning of brain size increase was the reshaping of the pelvic region, perhaps related to an increase in birth canal size to accommodate larger-brained fetuses. Evidence for tool manufacturing, meat eating, shelter building, and probably food sharing also occurs at about this time, which signals the coming of a new adaptive strategy.