‘Walking, Running and the Evolution of Short Toes in Humans’

by Aruna on  February 23, 2009 at 11:32 AM Research News
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 ‘Walking, Running and the Evolution of Short Toes in Humans’
Scientists have discovered the reason behind evolution of big toes in humans to the current small size.

According to biomechanical analysis, long toes require more energy and generate more shock than short toes, thus making them one of many adaptations that may have helped our savannah-dwelling ancestors chase their prey.

"Longer toes require muscles to do more work, and exert stronger forces to maintain stability, compared to shorter toes. So long as we were engaged in substantial amounts of running, natural selection would favour individuals with shorter toes," said University of Calgary anthropologist Campbell Rolian.

Unlike most primates, including our closest relative, the chimpanzee-humans have comparatively dwarfish and two-dimensional toes, capable only of extending and flexing, reports Wired News.

Even running animals have extremely short toes-some species, such as cats and dogs, have paws composed almost entirely by palms.

Thus, researchers tried to explain the human foot physiology on the basis of running.

"Humans are well-adapted for endurance running. That's much of what makes the human body what it is. We're actually terrible sprinters, but the world's best long-distance runners," said Lieberman.

Although, the long-runner hypothesis is not universally accepted, the new study does make a plausible case for the importance of toes for running.

During the moment of propulsion, when one foot is in the air and the other is on the ground, between one-half and three-quarters of a body's weight falls squarely on the forefoot.

"When you're walking, before you push off to start the next step, your other foot has already hit the ground. You've transferred some of your body weight. Your toes have to do much more work in running, to push you," said Rolian.

The researchers examined force exerted by fifteen test subjects running and walking on a pressure-sensitive surface, and found that increasing toe length by just 20 percent produced a doubling of motor force.

This can be explained in terms of the action of a seesaw, the distance between pressure and a fulcrum magnifies levering force.

Also, researchers found that longer toes require an additional energy investment when "braking," or using them to guide the forward-falling motion that underlies both running and walking.

The additional work required by long toes, and a resulting increase in muscle stress and damage, likely made them a victim of natural selection.

And the fossil record proved that the toes of great apes are longer than those of Australopithecus, the first bipedal hominid, which in turn are longer than the toes of Homo, the genus to which modern humans belong.

Hawks noted that long-distance running is now extremely rare, and "where it exists, it is supported by very sophisticated cultural adaptations, including tracking, water storage and staged transport of meat back to home bases. There is presently little or no evidence for these cultural adaptations in early Homo."

The study, titled "Walking, running and the evolution of short toes in humans," is published in the Journal of Experimental Biology.

Source: ANI

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