JOHNS HOPKINS (US) — Neandertals evolved with such short lower legs so they could move more efficiently over the mountainous terrain where they lived, a new study concludes.
The findings contradict the conclusion of earlier studies that short legs reduced total surface area and preserved body heat in the cold climate where the early human species lived. They also reveal a broader trend that may help explain the limb proportions of many different animals.
The research has been published online by the American Journal of Physical Anthropology.
“Studies looking at limb length have always concluded that a shorter limb, including in Neandertals, leads to less efficiency of movement, because they had to take more steps to go a given distance,” says lead author Ryan Higgins, a graduate student at Johns Hopkins University.
“But the other studies only looked at flat land,” Higgins says. “Our study suggests that the Neandertals’ steps were not less efficient than modern humans in the sloped, mountainous environment where they lived.”
Neandertals, who lived from 40,000 to 200,000 years ago in Europe and Western Asia, mostly during very cold periods, had a smaller stature and shorter lower leg lengths than modern humans.
Because mammals in cold areas tend to be more compact, with a smaller surface area, scientists have normally concluded that it was the region’s temperature that led to their truncated limbs compared to those of modern humans, who lived in a warmer environment overall.
Higgins’ work, however, adds a twist to this story. Using a mathematical model relating leg proportions to angle of ascent on hills, he has calculated that Neandertals on a sloped terrain would have held an advantage while moving compared to long-legged cousins such as modern humans.
Because the area Neandertals inhabited was more mountainous than where emerging modern humans tended to live, the researchers say that this assessment paints a more accurate picture of the Neandertals’ efficiency of movement as compared to homo sapiens.
“Their short lower leg lengths actually made the Neandertals more adept at walking on hills,” Higgins says.
But the research didn’t stop there.
“In our field, if you want to prove an adaptation to the environment, like mountains leading to shorter leg lengths, you can’t just look at one species,” Higgins says. “You have to look at many species in the same situation, and see the same pattern happening over and over again.
“We needed to look at other animals with similar leg construction that existed in both flat and mountainous areas, as Neandertals and humans did, to see if animals tended to have shorter lower leg length in the mountains.”
The researchers found, for instance, that mountainous bovids, such as sheep and mountain goats, overall have shorter lower leg bones than their relatives on flat land, such as antelopes and gazelles, even when they live in the same climates.
Investigating closely related bovids brought the trend into even sharper relief. Most gazelles live on flat land, but the one mountainous gazelle species examined had relatively shorter lower legs, despite sharing the same climate. Also, among goats and sheep, which mostly live on mountains, the one flat land member of the group exhibited relatively longer lower legs than all the others.
“Biologists have Bergman’s and Allen’s Rules, which predict reduced surface area to body size and shorter limbs in colder environments,” says Higgins. “Our evidence suggests that we can also predict certain limb configurations based on topography. We believe adding the topic of terrain to ongoing discussions about limb proportions will allows us to better refine our understanding of how living species adapt to their environments.
“This improved understanding will help us better interpret the characteristics of many fossil species, not just Neandertals.”
Funding for this research was provided by the Johns Hopkins Center for Functional Anatomy and Evolution.
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