Early humans 'still climbed trees 3m years ago'
27 October BBC
Early human ancestors were still climbing trees three million years
ago, according to a new study which contradicts previous assumptions
that they spent most of their lives on the ground.Fossilised shoulder
bones from a forerunner of humans known as Australopithecus afarensis,
the species of the famous "Lucy" skeleton, suggest that their bodies
were shaped by a life spent clinging on to branches with their hands.
From the shape of the species' feet it has long been clear that they
could walk on two legs, but experts have been unable to prove whether,
like their contemporary apelike species, they also spent part of their
lives in trees.
A study published last year claimed that A. afarensis's foot
structure was ill-suited to grasping branches and showed that by this
stage in human evolution, our ancestors had already abandoned climbing
behaviour.
But the new research, by experts from the California Academy of
Sciences and Midwestern University, suggests that the transition from
trees to a permanent life on solid ground occurred later than previously
thought.
A. afarensis, best known for the partial skeleton "Lucy" which was
discovered in Ethiopia in 1974, is seen as the best candidate for a
forerunner of humans living between three and four million years ago.
Lucy and her relatives had permanent arches in their feet, which enabled
them to stand and walk upright but would have prevented them from using
their big toes to grip onto branches. But the new study, published in
the Science journal, reveals that the species also had shoulder blades
which grew in a shape closer to modern apes than humans, suggesting that
they still used their upper limbs for balancing and climbing.Analysis of
a 3.3 million-year-old juvenile A. afarensis skeleton known as Selam,
discovered in Ethiopia in 2000, showed that it had the same distinctive
upward-pointing shoulder joints as adult Australopithecus and modern
apes, which are not shared by humans. The young specimen's shoulder
blade also had the same upward angle as adult fossils, whereas in humans
the angle decreases during growth because we rarely use our arms to
apply force or balance above head height.
The findings suggest that A. afarensis was still regularly using its
arms to climb and balance in trees and that the bone structure
previously seen in adults was not simply a redundant feature inherited
from earlier ancestors, researchers said.
Prof David Green, who led the study, said: "This study moves us a
step closer toward answering the question 'When did our ancestors
abandon climbing behaviour?' It appears that this happened much later
than many researchers had previously suggested."
|