Neanderthals, a close, heavy-set relative of Homo sapiens, lived primarily in Ice Age Europe, surviving on a high-protein diet of large animals. This, researchers say, triggered physical changes that distinguished Neanderthals from their modern human counterparts, namely a larger rib cage and wider pelvis.
A new study from Tel Aviv University revealed that the bell-shaped Neanderthal ribcage or thorax likely evolved to accommodate a larger liver - the organ responsible for metabolizing great quantities of protein into energy.
However, a heightened metabolism also required an expanded renal system - enlarged bladder and kidneys - to remove large amounts of toxic urea. This, researchers say, would have caused Neanderthals to evolve a wider pelvis.
While the anatomical differences between the thoraxes and pelvises of Homo sapiens and Neanderthals have been well known for many years, the recent study is the first to examine the role diet played in this evolutionary change.
"During harsh Ice Age winters, carbohydrates were scarce and fat was in limited supply. But large game, the typical prey of the Neanderthal, thrived," explained Miki Ben-Dor, a Ph.D. candidate in TAU's Department of Archaeology and Ancient Near Eastern Cultures. "This situation triggered an evolutionary adaptation to a high-protein diet -- an enlarged liver, expanded renal system and their corresponding morphological manifestations. All of these contributed to the Neanderthal evolutionary process."
Ben-Dor co-authored the recent study with Professors Avi Gopher and Ran Barkai.
"In a 2011 paper, which dealt with the demise of Homo erectus in the Levant, we had already tapped into the notion that diet played a major role in human evolution," Barkai added. "We argued then that high fat consumption was one of the most important solutions to the predicament presented by human evolution. Humans are limited in the amount of protein they are able turn into energy - protein provides just 30 percent of their overall diet. The solution, therefore, was to consume more fat and more carbohydrates when they were seasonally available."
In the case of Neanderthals, researchers found an acute shortage of carbohydrates and a limited availability of fat caused their biological adaptation to a high-protein diet. Furthermore, previous studies showed that a high-protein diet is likely to produce enlarged livers and kidneys.
"Early indigenous Arctic populations who primarily ate meat also displayed enlarged livers and the tendency to drink a lot of water, a sign of increased renal activity," Ben-Dor said.
It follows then that a total dependence on large animals for their fat and protein needs may have led to the eventual demise of Neanderthals, which occurred at about the same time large animals or "megafauna" went extinct in Europe some 50,000 years ago. Researchers plan to explore this further in future studies.
Their findings were recently published in the American Journal of Physical Anthropology.
