Running past Neandertals

Ancient humans, but not their evolutionary cousins, had heels for running

Stone Age people, unlike their Neandertal contemporaries, had heel bones spring-loaded for long runs, a new study suggests.

RUNNING HEEL An MRI of a distance runner’s foot and ankle shows a heel bone sized to pull the Achilles tendon taut, a condition that researchers say applied to Stone Age humans but not to Neandertals. Measurements of part of the heel bone (shown in red) helped scientists determine how easily an individual could run long distances. D. Raichlen

Neandertals weren’t left in the dust, though. The backs of their feet gave them a leg up on power walking, say anthropologist David Raichlen of the University of Arizona in Tucson and his colleagues.

In ancient Homo sapiens, as in people today, a short lower heel stretched the Achilles tendon taut, Raichlen’s team concludes. That arrangement increased the tendon’s spring-like action during running and reduced energy consumption, enabling extended excursions, the scientists report in a paper published online January 26 in the Journal of Human Evolution.

The result coincides with an earlier proposal that bodies suited to endurance running evolved in the genus Homo more than 2 million years ago because they aided hunting and carcass scavenging before spears were in widespread use, beginning sometime after 400,000 years ago (SN: 3/1/97, p. 134).

Raichlen’s team also finds that Neandertals, compared to people today, had tall heel bones that put a less energy-efficient spring in their steps while running. Neandertals’ tall heel bones possibly stabilized their ankles, giving them an advantage over Homo sapiens in walking uphill and jumping, the researchers hypothesize.

“We can say that energy costs of running differed between Neandertals and modern humans, but our data don’t really speak to the question of what happened to the Neandertals,” Raichlen says.

Scientists already knew that, relative to Stone Age people, Neandertals weighed more, had shorter legs and had smaller inner-ear canals that would have affected the balance needed to coordinate body movements, all obstacles to endurance running. Raichlen’s study “provides a new line of evidence that Neandertals were not as adept at long-distance running as modern humans were,” remarks anthropologist Herman Pontzer of Hunter College in New York City.

Reasons why modern humans evolved to run farther than Neandertals are unclear, Pontzer adds. Running prey to exhaustion may have worked better on hot African savannas where Homo sapiens lived than in cold European settings inhabited by Neandertals, he notes. But no heel fossils have been unearthed for any other Homo species, making it impossible to determine when running-friendly, spring-loaded feet like those of modern humans first evolved.

In their new investigation, Raichlen’s team calculated rates of oxygen consumption for eight experienced distance runners as they ran on a treadmill for 10 minutes at 16 kilometers per hour (10 miles per hour). On a separate day, an MRI scanner took images of each man’s heels and Achilles tendons.

Volunteers displayed short lower heel bones, especially the runners who used oxygen most efficiently while running.

Heel-bone measurements of 13 fossil Homo sapiens that lived between approximately 30,000 and 100,000 years ago resemble those of today’s runners, the scientists say. On average, the measurements indicate that the ancient humans expended 6.9 percent more energy while running than their counterparts today did — not a substantial difference, according to the researchers.

Analyses of heel bones of six Neandertals from the same time period indicate that these hominids used an average of 11.4 percent more energy while running than modern athletes did, a statistically notable disparity, Raichlen says.

Energy efficiency while running depends far more on a person’s anatomy than on physical training, the researchers say. They used distance runners as a modern comparison group in order to account for any training effects.

Bruce Bower has written about the behavioral sciences for Science News since 1984. He writes about psychology, anthropology, archaeology and mental health issues.

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