Friday, October 02, 2009

Oldest Human ancestor discovered

How old are humans? Until recently I thought Lucy to be our oldest ancestor, that is around 3.9 to 2.9 million years old. A recent finding by a group of scientists reveals our oldest known ancestor "Lucy" is now replaced by "Ardi"(Ardipithecus ramidus) which is older by 1.4 million years than Lucy.This individual, 'Ardi,' was a female who weighed about 50 kilograms and stood about 120 centimetres tall.

In its 2 October 2009 issue, Science presents 11 papers, authored by a diverse international team, describing an early hominid species, Ardipithecus ramidus, and its environment. These 4.4 million year old hominid fossils sit within a critical early part of human evolution, and cast new and sometimes surprising light on the evolution of human limbs and locomotion, the habitats occupied by early hominids, and the nature of our last common ancestor with chimps.

Science is making access to this extraordinary set of materials FREE (non-subscribers require a simple registration). The complete collection, and abridged versions, are available FREE as PDF downloads for AAAS members, or may be purchased as reprints.

The last common ancestor shared by humans and chimpanzees is thought to have lived six or more million years ago. Though Ardipithecus is not itself this last common ancestor, it likely shared many of this ancestor's characteristics. Ardi is closer to humans than chimps. Measuring in at 47 in. (120 cm) tall and 110 lb. (50 kg), Ardi likely walked with a strange gait, lurching side to side, due to lack of an arch in its feet, a feature of later hominids. It had somewhat monkey-like feet, with opposable toes, but its feet were not flexible enough to grab onto vines or tree trunks like many monkeys -- rather they were good enough to provide extra support during quick walks along tree branches -- called palm walking.

Another surprise comes in Ardi's environment. Ardi lived in a lush grassy African woodland, with creatures such as colobus monkeys, baboons, elephants, spiral-horned antelopes, hyenas, shrews, hares, porcupines, bats, peacocks, doves, lovebirds, swifts and owls. Fig trees grew around much of the area, and it is speculated that much of Ardi's diet consisted of these figs.

The surprise about the environment is that it lays to rest the theory that hominids developed upright walking when Africa's woodland-grassland mix changed to grassy savanna. Under this now theory, hominids began standing and walking upright as a way of seeing predators over the tall grasses. The discovery of Ardi -- an earlier upright walker that lived in woodland -- greatly weakens this theory.

Scientists have theorized that Ardi may have formed human-like relationships with pairing between single males and females. Evidence of this is found in the male's teeth, which lack the long canines that gorillas and other non-monogamous apes use to battle for females. Describes Professor Lovejoy, "The male canine tooth is no longer projecting or sharp. It's no longer weaponry."

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