18th February 2011, 09:20 PM
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|  Evolution| Meet our collective mother | Here's Lucy
 WALKING TALL: An artist's impression of what the species known as Australopithecus afarensis may have looked like. It is based on the 3.2 million-year-old partial skeleton dubbed 'Lucy'. Picture: AFP Photo Source: AFP Evolutionary theory told to take a walk | Courier Mail Quote:
February 12, 2011
IT was a small step for an apeman, but a giant leap for mankind.
Scientists have pinpointed the moment when our ancestors finally abandoned the trees to walk upright.
In a breakthrough that helps rewrite human evolution, researchers have found a fossilised foot bone from an early human relative who strolled confidently on two legs about 3 million years ago.
The finding ends decades of debate about when our ancestors first began to walk like modern man, rather than clambering around the trees like monkeys.
The newly discovered bone is a complete fourth metatarsal - one of the long bones that connects the toe to the base of the foot.
The fossilised bone belonged to Australopithecus afarensis - best known from the discovery of "Lucy", whose partial skeleton was dug up in Ethiopia in 1974.
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Previously, experts believed that homo erectus was the first member of the family tree to walk upright, between 1.8 million and 70,000 years ago.
But this discovery confirms that the development actually took place between one and two million years earlier.
The fossil shows that Lucy's feet had fixed arches, a trait only found in humans and which evolved to cope with running and walking long distances.
Dr Carol Ward from the University of Missouri, who led the study, said: "Now that we know Lucy and her relatives had arches in their feet, this affects much of what we know about them, from where they lived to what they ate and how they avoided predators.
"The development of arched feet was a fundamental shift towards the human condition, because it meant giving up the ability to use the big toe for grasping branches, signalling that our ancestors had finally abandoned life in the trees in favour of life on the ground."
Lucy's species are estimated to have lived between 3.7 million and 2.9 million years ago and were known to be able to walk on two feet.
However, researchers did not know whether they spent most of their time on all fours or upright.
Dr Ward said: "Arches in the feet are a key component of human-like walking because they absorb shock and also provide a stiff platform so that we can push off from our feet and move forward."
The discovery of the bone, in Hadar, Ethiopia, is reported in the journal Science.
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