'Humans Learned to Walk in Trees'
May 31
Humans learned to walk upright in the trees, not on the open land, experts have said.
The new theory marks a U-turn in scientific thinking. Previously it was assumed humans only began to stand upright after moving out of the forests on to the wide open savannahs of
East Africa.
Moving on two legs was thought to have evolved slowly from the all-fours "knuckle-walking" displayed by chimpanzees and gorillas today. But a study of orang-utan behaviour, published in the journal Science, suggests this is wrong, according to a British team of scientists from Liverpool and Birmingham universities.
They believe knuckle-walking evolved only recently as a way of getting around the forest floor. Walking on two legs, assisted by the support of branches, appeared to be an older trait which evolved from foraging for food in tree tops.
According to the new theory, bipedalism was always a feature of great ape behaviour. Humans inherited it without ever passing through a knuckle-walking phase.
Skeletons of early human ancestors show a combination of short legs and
long arms, which are adaptations for tree-living.
To understand why walking on two legs might have evolved in tree-living apes, the scientists turned to the Sumatran orang-utan - the sole modern great ape that only inhabits trees. They found that the orang-utan uses bipedalism to fetch food from the small branches of tree tops, and to cross directly from one tree crown to another.