Bone strength reveals how human ancestors moved
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An international research team led by the Keck School of Medicine of USC studied fossils from seven human ancestors, members of the Australopithecus and early Homo groups, to understand how they moved and lived between 1.5 and 3.7 million years ago. The scientists used CT scans to measure the strength of arm and thigh bones, knowing that bone adapts to the stresses of movement.
They compared the bone strength in the upper and lower limbs to determine how much time these ancestors spent in trees versus walking on the ground. Researchers discovered that Australopithecus combined traits of both apes and humans. They possessed strong arm bones, indicating frequent tree climbing, but also had leg bones showing a pattern of upright walking similar to modern humans. This suggests Australopithecus had a unique method of movement not seen in any living species.
In contrast, early Homo individuals, who lived more recently, exhibited stronger leg bones and weaker arm bones, mirroring the pattern found in modern humans. The team proposes that this change in limb strength represents a key behavioral shift between the two groups. This shift may also be linked to the increase in brain size that occurred around two million years ago, as increased walking could have placed new demands on the body and brain.
