Neanderthals and humans were kissing cousins, literally, but they had their anatomical differences, among them wider pelvises and rib-cages. Now archaeologists from Tel Aviv University suggest that the reason for these anatomical discrepancies is that Neanderthals ate mostly meat, while Homo sapiens has had a more variegated diet.
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It isn't new that the Neaderthal ribcage and pelvis are wider than man's. But until now scientists had assumed that had to do with Neanderthals having greater energetic demands than Homo sapiens. Whether or not that was a factor, the Tel Aviv archaeologists think the reason may have been more diet-oriented.
Studies of coprolites (fossil feces) have shown that Neanderthals, who lived among European and Middle Eastern humans until around 30,000-40,000 years ago, also ate plant matter. But a range of studies have shown the Neanderthal diet to be heavily biased towards protein – meat and fat. Chemical studies of their bones has indicated that a bigger proportion of their diet came from meat than cave bears found at the same sites; analysis of the isotopes in Neanderthal collagen shows their diet consisted mainly of herbivores, and megafauna, such as sloths, mammoths and prehistoric rhinoceroses, as well as plants.
In the frigid winters of the Ice Age, large animals may have flourished, but their fat content would have been reduced. A theoretical model created by the Israeli scientists predicts that during glacial winters, when carbohydrates weren’t available and fat was scarce, the Neanderthals needed to get more caloric intake meat, and evolved to better convert the protein into life-giving energy.
To contend with all that protein, their livers, which are responsible for protein metabolism, had to become larger. So their lower thoraxes did too.
The more protein is metabolized, the more toxins such as urea need removal from the body. As their protein metabolism increased, the Neanderthals needed more renal capacity – an enlarged bladder and kidneys – to get rid of the toxins, could, evolutionarily, be the reason why the Neanderthal pelvis is wider than ours.
"Given that high protein consumption is associated with larger liver and kidneys in animal models, it appears likely that the enlarged inferior section of the Neanderthals' thorax and possibly, in part, also his wide pelvis, represented an adaptation to provide encasement for those enlarged organs," write the scientists.
"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 points out.
Why the Neanderthals eventually went extinct is not known. They also ate whatever herbivores they could catch, not only giant animals. But among the many theories is that their demise is related to the extinction of the megafauna, which disappeared just before they did, around 50,000 years ago. We don't know precisely why the megafauna went extinct either but one postulation is that the climate changed in ways they found uncomfortable, and they were hunted to death. If so, that may have doomed the Neanderthals in their turn.