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Humans' heel-down posture provides fighting advantage

"The shape of our feet is one of a series of distinguishing anatomical traits, from our faces to our heels, that increase fighting performance," said biologist David Carrier.

By Brooks Hays

Feb. 15 (UPI) -- While other primates walk on the balls of their feet, humans and great apes rely on their heels for postural support. New research suggests the adaptation offers a measurable advantage when fighting.

Previous studies have emphasized the role aggression and fighting played in shaping the evolution of human anatomy.

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"This story is one more piece in a broader picture, a suite of distinguishing characters that are consistent with idea that we're specialized at some level for aggressive behavior," David Carrier, a biologist at the University of Utah, said in a news release.

Carrier and his colleagues have previously suggested the evolution of human fists was driven as much by the necessity of punching as by the advantages of improved dexterity. Likewise, his previous research showed the human face evolved to better withstand violent blows.

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Carrier teamed up with researchers at the University of Georgia to find out whether aggression played a role in the adoption of heel-down, or plantigrade, posture among great apes and humans.

Most primates, and many mammals, employ digitigrade and unguligrade postures, both of which put weight on the balls of the feet. The postures are conducive to running and sprinting.

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But as the new research confirmed, plantigrade posture allows users to generate more powerful strikes with the arms.

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Researchers had volunteers push on a pendulum, alternating between elevated and planted heels. The pendulum allowed scientists to measure the forces generated, or amount of work done, using each posture. The volunteers repeated the experiment while wearing a fuzzy sock and standing on a sheet of teflon, minimizing friction and diminishing the ability to generate force from the ground.

Volunteers were able to generate more force using a heel-down posture during both experiments.

Scientists say their findings -- detailed in the journal Biology Open -- are in line with other studies that suggest aggression shaped the anatomical evolution of early humans and their great ape ancestors.

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"Certain species tend to be good at fighting or fleeing, but not both," added Emily Carrington, a program director in the National Science Foundation. "This study provides insight into the basis for this trade-off. Animals that are able to use their heels to plant their feet firmly to the ground, like bears, badgers and great apes, are able to deliver stronger blows to their opponents."

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