Human Origins / Human Evolution

If the South African foot suggests that Lucy and her kin still spent part of their time in trees, another 1995 discovery indicates that hominids much earlier than A. afarensis could already walk on two feet. Until now the oldest evidence of bipedalism was the fossil footprints at Laetoli, Tanzania, which are believed to have been left 3.6 million years ago by A. afarensis. But last summer a team of paleontologists led by Meave Leakey, a member of the famed fossil-hunting clan, announced that they’d found a new species of human ancestor that predates A. afarensis by about half a million years. Leakey and her colleagues call the new hominid Australopithecus anamensis. The word anam means lake in a Kenyan dialect; the fossils--including some teeth, parts of the upper and lower jaws, an arm bone, and these two pieces of a shinbone--were found near Lake Turkana in northern Kenya. The shinbone, or tibia, shows that the creature spent a fair amount of its time walking upright, says Penn State paleontologist Alan Walker, who worked with Leakey. If you look at a chimpanzee tibia, says Walker, you’ll see that it is shaped like a T instead of a trumpet. Below the knee joint it narrows down quickly to the shaft. In humans--and in anamensis--says Walker, the tibia is thicker and designed to bear the stress of an upright stance. Leakey and Walker are now back at Lake Turkana, where they hope to find more evidence of when our ancestors first parted ways with their quadrupedal relatives.