October 24, 2011
Neanderthals are often thought of as being cavemen, but “mountain men” may be more appropriate. A recent study suggests at least some Neanderthal features may have been adaptations to living in mountainous terrains.
Neanderthals had relatively shorter limbs than modern humans. Traditionally, scientists have thought that this and other aspects of the Neanderthal body evolved in response to living in cold climates in Eurasia. Short limbs reduce the surface area through which heat can escape, which would have allowed Neanderthals to conserve body heat. This principle is known as Allen’s rule.
Having shorter legs would have put Neanderthals at a disadvantage compared to longer-limbed humans that evolved in tropical Africa, where conserving heat is not a problem. That’s because people with shorter legs take proportionally smaller steps than people with longer legs; therefore, Neanderthals would have expended more energy while walking because they had to take more steps.
But Ph.D. student Ryan Higgins and biological anthropologist Christopher Ruff, both at Johns Hopkins University, wondered if Neanderthals were always at a disadvantage. Previous research had focused on walking on flat surfaces. Yet “archaeological evidence suggests a difference in landscape usage between Neanderthals and early modern humans,” Higgins says. “Terrain seems important to consider since a larger percentage of Neanderthal sites are caves and rock shelters.”
Higgins and Ruff investigated the walking efficiency of Neanderthals and modern humans in a mountainous terrain using a mathematical model. They found the advantage humans had walking on flat surfaces disappears when walking uphill (they considered a 30 degree slope, equivalent to walking up a typical staircase). In sloped terrains, Neanderthals and humans were equally efficient, the team reported in the American Journal of Physical Anthropology. That’s because in addition to having shorter legs overall, Neanderthals had shorter lower legs (shins) relative to their upper legs (thighs). People with shorter lower legs don’t need to swing their legs as high for a given footstep while walking uphill. “Thus, for a given step length they will need to put in less effort,” Higgins says, “or for the same effort they will have a larger step length and will ultimately take fewer steps to go a given distance.”
This phenomenon isn’t unique to Neanderthals. Higgins and Ruff also looked at hoofed animals. Goats, gazelles and antelopes that live in mountainous environments have shorter lower legs than their counterparts in flat environments. This is true in both cold and warm climates—evidence that mountain living, not climate, probably drove the evolution of shorter lower legs in these animals.
This may be the case for Neanderthals, too. Although having an overall shorter leg (shin and thigh) might have been an adaptation for cold climates, having a shorter lower leg compared to upper leg might have been an adaptation for mountainous terrains. To test the idea further, Higgins says he is now starting to measure energy expenditure in people with different leg proportions while walking on flat versus sloped surfaces.
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