Prior to the year 2000, the dominant paradigms of hominid origins could be summarised as follows: (a) the African ape/human (AAH) dichotomy occurred about 5 Ma, perhaps 6 Ma for some authors, or as young as 2.5 Ma for others; (b) the precursors of hominids were probably quadrupedal, terrestrial apes; (c) the AAH transition likely took place in the savannah; (d) the last common ancestor (LCA) of African apes and humans looked like a chimpanzee (prolonged face, enlarged canines in males, knuckle-walking locomotion and black body coats); and (e) there was an australopithecine stage between the LCA and the genus Homo.

The discovery of the 6 million-year-old bipedal hominid Orrorin in the Lukeino Formation, Kenya, in 2000, and in particular its femora, which showed that it was fully bipedal, was bound to pose serious challenges to all these paradigms. Given that Orrorinis almost twice as old as Lucy (AL 288–01, Australopithecus antiquus, which is possibly a species different from Australopithecus afarensis in which it is usually classified) (Ferguson, 1984) and almost 2 million years older than Ardipithecus ramidus ramidus, it would be surprising if it didn’t upset the apple cart to some extent. Further studies in the Lukeino Formation reveal that most previous ideas concerning remote hominid origins need to be modified or refined. Not only their biological aspects, but also their chronological and environmental aspects require rethinking.