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Human evolution

We are what we ate

Nature volume 400, pages 219–220 (1999)Cite this article

Much of evolutionary history involves the fine-tuning of variations on a common theme. But every now and again significant innovations (known as grade shifts) occur, forming the basis for the next phase of evolutionary activity. Evidence of such a grade shift in human evolution can be found in the fossil record of a little less than two million years (Myr) ago. Here we see the first signs of hominins (human ancestors from the tribe Hominini) whose bodies, jaws and teeth begin to resemble those of modern humans. Writing in the Journal of Human Evolution, O'Connell and colleagues1 now challenge conventional wisdom by suggesting that the cascade of changes — involving anatomy, life history, culture and social structure — that resulted in the evolution of modern humans was set off not by hunting, but by systematic exploitation of subterranean food sources and recruitment of grandmothers to provide for their grandchildren.

The most primitive hominin known, the 4.5-Myr-old Ardipithecus ramidus3, has relatively few derived hominin features. It is probably just one of a number of early hominins with different combinations and degrees of emphasis on ‘human’ features such as thickened enamel, upright posture and skeletal adaptations to a more terrestrial locomotion. After A. ramidus, but before 2 Myr ago, all species of hominin are megadont (that is, they have larger chewing teeth) compared with living modern humans and chimpanzees. But they differ in absolute and relative brain size, in the degree of megadonty, and in the extent to which the post-cranial skeleton shows adaptations to an upright posture and bipedalism4. There are probably undiscovered hominin species with different combinations of these adaptations.

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Figure 1: Species considered to be part of the tribe Hominini, or hominins, as opposed to chimpanzee ancestors, or panins.

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  1. Department of Anthropology, George Washington University, DC 20052, Washington, USA

    Bernard Wood & Alison Brooks

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  2. Alison Brooks
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Wood, B., Brooks, A. We are what we ate. Nature 400, 219–220 (1999). https://doi.org/10.1038/22227

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