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In Brief

Ardipithecus makes the cover

Joe McCall finds yet more news from Afar…

Geoscientist 20.02 February 2010

The Afar area in Ethiopia seems unable to keep out of the news. Leaving aside the question of whether there is a new ocean forming there1 yet another major discovery of hominid remains has upstaged the famous ‘Lucy’ and completely altered our conception of our ancestry. Researches through the 1990’ uncovered more than 100 fossils of a ~4.4Ma creature named Ardipithecus ramidus2,3, including a near-complete skeleton. This predates ‘Lucy’ (also discovered there) which was only 3.2 million years old.

A. ramidus is not the oldest known hominid. There is an older thigh bone dated at ~6Ma named Orrorin tugenensis, from the Chemeron Formation (which Baker, Walsh and McCall recognised and named4 when they discovered that Leakey’s ‘Kamsia Formation’, Baringo District, Kenya, supposed deposits of a huge pre-existing lake, was actually two formations, laid down millions of years apart). There is also a skull from the Chad region, Sahelanthropus tchadensis, dated at ~7Ma; but the wealth of A. ramidus material recovered has allowed a complete reassessment of the story of our ancestors. This new hominid stood 120cm tall and had a small brain - equivalent to that of a female chimpanzee - at ~300 cubic centimetres.

This discovery puts to rest the notion, which has plagued us Darwin’s time that a chimpanzee-like “missing link” would one day be found. Chimpanzee anatomy and behaviour is now largely irrelevant to our beginnings. The second important point is the creature’s bizarre method of locomotion. Its feet, legs and hands suggest that it was a biped on the ground, but moved as a quadruped in the trees. The big toe splays out like an ape’s, the better to grasp the trees; but modifications to its toes allowed it to walk bipedally (though less efficiently than ‘Lucy’). Even in the trees, A. ramidus, was nothing like a modern ape, walking there on its palms. This represents an intermediate stage in our evolution, about which no one hitherto suspected.

The team also found ~6000 animal fossils, including monkeys and antelope, which lived in forests, including figs and palm trees, at that time. This apparently sounds the death knell of the ‘savannah hypothesis’, which holds that primitive hominids walked upright because forest gave way to grassland. However William Jungers, of Stony Brook University, New York State has reservations about its bipedality. “Divergent big toes are associated with grasping, and this has one of the most divergent big toes you can imagine: why would an animal fully adapted to support its weight in the trees elect to walk bipedally on the ground?” he asks.

Well, one school of thought attributes the adoption of bipedality to the adoption of monogamy, so clearly there will be arguments about A. ramidus for years to come. However there is no question that these finds are of the greatest importance. Alan Walker, of Pennsylvania State University, who is not one of the team, remarked that: “It shows that the last common ancestor with chimps did not look like a chimp, or a human, or something between.”

The finds were announced in joint press conferences in Washington and Addis Ababa and published in a set of papers in a special issue of Science.


  1. McCall, G J H 2006. Tales from Afar. Geoscientist 16(7), 8-9.
  2. Shreeve, J Oldest skeleton of human ancestor found
  3. Wayman, E 2009. Before Lucy: older hominid Ardi challenges thinking about human evolution. Earth 54(12), 8-9.
  4. McCall, G J H, Baker, B H , Walsh, J 1967. Late Tertiary and Quaternary Sediments of the Kenya Rift Valley. In: Bishop, W.W. & Clark, J. Desmond, eds., “Background to Evolution in Africa”. The University of Chicago Press, Chicago and London, pp 191-220.