Wednesday, January 2, 2013

Our ancestor, Lucy, divided her time between trees and ground

n this August 14, 2007 photo, a three-dimensional model of the 3.2 million-year-old hominid known as Lucy is unveiled at the Houston Museum of Natural Science.

Researchers believe they have solved one of the biggest puzzles in anthropology — whether Lucy, one of our famous ancestors, lived in the trees or on the ground.

Australopithecus afarensis, better known as Lucy, is believed to have walked the Earth 3.2 million years ago in Africa, and scientists based their model on a skeleton discovered in Ethiopia in 1974.

Researchers have long argued over when our ancestors came down from the trees, with arguments centring on Lucy, and whether her feet allowed her to climb as well as walk.

Now, scientists studying the feet of Ugandan hunters who climb for honey say they believe Lucy may have spent time in both trees and on ground, the Daily Mail reported.

Many researchers view terrestrial bipedalism, the ability to walk on two legs on the ground, as the hallmark of ‘humanness’ as most of our living primate relatives — the great apes, specifically — still spend their time in the trees.

Humans are the only member of the family devoted to the ground, living terrestrial rather than arboreal lives, but that wasn’t always the case.

The fossil record shows that our predecessors lived in trees — until Lucy arrived on the scene — and it was her knee joint that led to the discovery that Lucy was one of the first bipeds.

“Australopithecus afarensis possessed a rigid ankle and an arched, non-grasping foot,” wrote Nathaniel Dominy and his co-authors in Proceedings of the National Academy of Sciences.

“These traits are widely interpreted as being functionally incompatible with climbing and thus definitive markers of terrestriality,” said Mr. Dominy, an associate professor of anthropology at Dartmouth.

The team carried out field studies on modern humans who have feet adapted to terrestrial bipedalism and found these people can still function as effective treeclimbers.

The studies in Uganda compared Twa hunter-gatherers to their agriculturalist neighbours, the Bakiga. In the Philippines, the researchers studied Agta hunter-gatherers and Manobo agriculturalists.

Both the Twa and the Agta habitually climb trees in pursuit of honey, a nutritious component of their diets.

Among the climbers, Mr. Dominy and his team found a phenomenon known as extreme dorsiflexion-bending the foot upward toward the shin to an extraordinary degree — beyond the range of modern ‘industrialised’ humans.

“Assuming their leg bones and ankle joints were normal, we hypothesised that a soft-tissue mechanism might enable such extreme dorsiflexion,” the authors write.

They tested their hypothesis and found that the climbing Agta and Twa have significantly longer muscle fibres.

The results suggest that a terrestrially adapted foot and ankle do not exclude climbing from the behavioural repertoire of human hunter-gatherers, or Lucy.