Fossil remains discovered recently in Kenya show that prehumans were walking on two legs at least 4 million years ago, far earlier than previously theorized, scientists announced Wednesday.
The fossils, uncovered at two sites near Lake Turkana, present the earliest direct evidence of bipedalism, which many anthropologists believe was crucial in the long evolutionary process that produced today’s humans.
Anthropologist Meave Leakey said at a news conference in Nairobi that the fossils her team found “show very clearly that 4 million years ago our ancestors did not swing around like apes” in the trees. Leakey works with the National Museums of Kenya, in Nairobi.
Until now, the oldest direct evidence of upright walking came from ancient footprints preserved in volcanic mud at a Tanzanian site called Laetoli. The 3.5-million-year-old footprints were found in 1978 by Mary Leakey, widow of famed anthropologist Louis Leakey, mother of fossil-hunter Richard Leakey, and mother-in-law of Meave Leakey.
William Kimbel, director of science at the Institute of Human Origins in Berkeley, Calif., called the find “extremely important … Any contribution to the record of evolution over 4 million years old is important because it fills what has been a virtual void in our information.”
Paleo-anthropologist Alan Walker, a co-author of the report in the journal Nature, explained that bipedalism is so crucial because it was perhaps “a key human adaptation; it may turn out to be the adaptation that makes the difference between apes and humans.”
Walker, at Pennsylvania State University, said the new fossils and the environment in which they were found also indicate that the prehuman creatures lived among trees, not out in open grasslands.
Scientists once speculated that bipedalism arose as prehumans left the forests to hunt in the savannahs, forcing them to stand on hind legs to see over tall grass. Bipedalism also frees the hands for other uses, such as carrying things, making tools and using weapons.
Walker also noted that the new creature, identified via bones and teeth, is now the oldest known representative of the prehuman Australopithicus line. Walker, Meave Leakey and their colleagues gave it the name A. anamensis, derived from the word “lake” in the Turkana language in Africa. Their search was financed by the National Geographic Society.