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12 | NewScientist | 3 April 2010 T. rex relatives lived down under With heels like these, we were born to run IN THE Greek myth, the heel was Achilles’ fatal flaw, but it may prove to be a key asset for finding out when our ancestors first ran on two feet. A well-developed Achilles tendon, it turns out, is crucial for this distinctively human mode of locomotion. Modern humans are unusually good long-distance runners: over distances of tens of kilometres, well-trained athletes can outrun a horse. Bill Sellers of the University of Manchester, UK, created a computer model of human hips and legs, including the tendons and muscles. The “legs” were made to learn to run using trial and error, allowing CARLOS HERNADEZ/AURORA/PLAINPICTURE IN BRIEF The future, predicted by your brain the muscles to contract at different times. After thousands of iterations, a fairly lifelike running motion developed. To see how important elastic tendons are to this gait, Sellers then made all tendons in his model 100 times stiffer. This more than tripled the legs’ energy use per metre and nearly halved their top speed. He then restored normal elasticity to the Achilles tendon only. “Even if the only tendon you have working is the Achilles tendon, the model is capable of fairly competent running,” Sellers says (International Journal of Primatology, DOI: 10.1007/s10764-010-9396-4). Tendons do not fossilise well, but they leave traces where they attach to the bone. Sellers says these might be detectable in fossils of early humans, making it possible to discover when we became runners. The water’s foul but bugs seem to like it
