Tree-climbing girl turns man's history on its head
The fragile remains of a three-year-old girl who died about 3.3
million years ago in East Africa have revealed that our early human
ancestors still spent much of their time in the trees long after they
had fully mastered the art of walking on two legs.
The discovery appears to have finally ended the debate over whether
this bipedal hominid still continued to climb trees, much like their
earlier ape ancestors.
The fossilised shoulder blades and arm sockets belonging to Selam,
meaning "peace", indicate that she and her family continued to climb
trees like modern apes even though her lower body was perfectly adapted
to upright walking.
Scientists believe that the upward angle of her arm sockets and
ape-like shoulder blades suggest that she was an active tree climber.
This means that humanity's earliest ancestors abandoned an arboreal
existence far later in our evolutionary history than previously thought.
Selam is a remarkably well-preserved specimen of the species
Australopithecus afarensis, an important forerunner of the human
lineage.
Her almost-complete skull and skeleton, embedded in sandstone rock,
was discovered in 2000 in the Dikika region of northeast Ethiopia and it
has taken years of painstaking work for scientists to extract the
fossilised bones from the stone.
The latest study, published in the journal Science, reveals the first
complete set of shoulder blades of Australopithecus afarensis.
"The question as to whether Australopithecus afarensis was strictly
bipedal or if they also climbed trees has been intensely debated for
more than 30 years," said Prof David Green, curator in anthropology at
the California Academy of Sciences and one of the authors of the study.
"These remarkable fossils provide strong evidence that these
individuals were still climbing at this stage in human evolution," Prof
Green said.
Trees were probably still an important refuge from the many large
predators that roamed the land at the time.
Trees were especially important for females nursing infants,
especially at night.
Humans and apes shared their last common ancestor about 6.5 million
years ago. The discovery in the same region of Ethiopia in 1974 of the
first Australopithecus skeleton, a female called Lucy, showed that
upright walking on two legs had evolved more than three million years
ago, long before the emergence of the human genus "Homo" about a million
years later.
Zeresenay Alemseged of the California Academy of Scientists, the
scientist who first discovered Selam, has spent the past 11 years trying
to extricate the bones, especially her fragile shoulder blades, from
their sandstone tomb.
"Because shoulder blades are paper thin they rarely fossilise, and
when they do they are almost always fragmentary.
Finding both shoulder blades completely intact and attached to a
skeleton of a known and pivotal species was like hitting the jackpot,"
Dr Alemseged said.
"This study moves us a step closer towards answering the question
'when did our ancestors abandon climbing behaviour?' It appears that
this happened much later than many researchers have previously
suggested," he said.
Descending from the trees and learning to walk upright on two legs is
considered one of the defining moments in human evolutionary history
that set our distant ancestors on the path towards sophisticated took
making, the control of fire and complex social behaviour.
"This new find confirms the pivotal place that Lucy and Selam's
species occupies in human evolution. While [they were] bipedal like
humans, A. afarensis was still a capable climber. Though not fully
human. A. afarensis was clearly on its way," Dr Alemseged said.
Although chimps and modern humans shared their last common ancestor
about 6.5m years ago, it was only just over two million years ago that
the first humans emerged in the form of Homo habilis, or "handy man", a
tool-making species with half the brain size of modern man.
- The Independent
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