Early hominin takes over Science magazine

I first mentioned Ardipithecus ramidus in EPN for February 2002 (Taking stock of hominid evolution), and the remarkable first finds by Tim White and his team were in 1994. Fifteen years on, and having amassed fragments of at least 36 individuals (and thousands of vertebrate, invertebrate and plant fossils) – Owen Lovejoy of Kent State University remarked, ‘This team seems to suck fossils out of the ground’ – it’s pay day! A total of 54 pages of the 2 October 2009 issue of Science (v. 326, Issue 5949) are devoted to this diminutive and very old (4.4 Ma) hominin. Such mounds of data wrested from the cauldron of the Afar Depression needed a long incubation period, and what is presented in Science is a summary rather than being comprehensive: much more is available online, and yet to come. The now hugely experienced, 47-strong academic team built up by Tim White and his original colleagues deserve massive congratulations. But they depended on the eagle-eyed, mainly Ethiopian fossil finders, many of whom are Afar pastoralists who took to field palaeontology as ducks to water. Science in general owes a massive debt to all those who have wrested such a wealth of anatomical information from every aspect of the fossils and their environmental context. What they have achieved is more worthy of Nobel-status than the fumbling of gaggles of annual economist-laureates who still cannot grasp why the world economy continually does grave disservice to humanity. The Ar. ramidus team also have a lot more worth saying to us than those physicists who seek the grail of a theory of everything – racked by such hubris that they are both unintelligible and unrealistic in the most literal way.

I cannot do adequate justice to the work in that historic issue of Science, but there are some general points that will leave any interested person breathless. As regards previous assumptions about the environment under which hominins emerged, it was woodland not open savannah. Though upright and capable of walking, as revealed by pelvis remains, Ardipithecus had feet with opposable big toes: sort of foot-thumbs. So they would have been as comfortable on trees as on the ground. Yet, their foot-architecture shows signs of having evolved from  monkey-like feet rather than any lin=ke those of modern gorillas and chimps. A degree of certainty accompanies anatomical discussions, for one individual female Ar. ramidus is represented by a large proportion of a full skeleton, rivalling the later remains of  ‘Lucy’, an Australopithecus afarensis. Her skull, reconstructed from a badly crushed state using co0mputed tomography and digital piecing-together, gives a brain size around the same as bonobo chimpanzees, and less than that of australopithecines. The feet clearly show a walker able to clamber, rather than swing and knuckle walk. Hands, though primitive, are more human-like than those of living apes are. From that can be concluded that a common ancestor a million of so years earlier was not ape-like in manual terms: chimps have evolved in this respect perhaps a lot more than those on the human line. Teeth shape, wear and isotopic signatures suggest a broad diet, rather than specialisation, from which grasses and grass-eating prey seem absent. Moreover, there is no sign of large canines, that could indicate minimal social aggression. Males and females were of similar size, as are we, rather than showing the sexual dimorphism that characterised later australopithecines and both chimps and gorillas. This also seems to point backwards in time to the last common ancestor of ourselves and chimps being very different from both living genera. Yet in many respects chimps seem to have evolved more than hominins. Because of the work on Ar. Ramidus, a chimpanzee-centric view of our shared forebears and therefore of hominin evolution can now be rejected. Perhaps thankfully, speculation about aspects of our behaviour stemming from those of chimpanzees is probably worthless.

The mass of data concerning this small, Pliocene hominin holds out a promise of yet more to come, both further back in time, and to populate the gaps in time and morphology that currently plague palaeoanthropology. The terrestrial sediments in which White et al. found Ar. Ramidus are 300 m thick, cover 5.5 to 3.8 Ma and are exposed over a large area. The stratum from which most data were recovered represents at most about 10 thousand years. Elsewhere in the Afar-Danakil Depression are other sediments laid down in river and lake systems that go back as far the Miocene (the estimated time of the last common ancestor of other primates and humans), and are still being deposited today. If anything characterised this triumph of the human intellect, it combined patience, determination and an attention to detail that was shared by every participant.

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