Neandertals' large lower thorax may represent adaptation to high protein diet

Abstract

Humans are limited in their capacity to convert protein into energy. We present a hypothesis that a "bell" shaped thorax and a wide pelvis evolved in Neandertals, at least in part, as an adaptation to a high protein diet. A high protein diet created a need to house an enlarged liver and urinary system in a wider lower trunk. To test the hypothesis, we applied a model developed to identify points of nutritional stress. A ratio of obligatory dietary fat to total animal fat and protein sourced calories is calculated based on various known and estimated parameters. Stress is identified when the obligatory dietary fat ratio is higher than fat content ratios in available prey. The model predicts that during glacial winters, when carbohydrates weren't available, 74%-85% of Neandertals' caloric intake would have had to come from animal fat. Large animals contain around 50% fat calories, and their fat content is diminished during winter, so a significant stressful dietary fat deficit was identified by the model. This deficit could potentially be ameliorated by an increased capability to convert protein into energy. 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 Neandertals thorax and possibly, in part, also his wide pelvis, represented an adaptation to provide encasement for those enlarged organs. Behavioral and evolutionary implications of the hypothesis are also discussed. Am J Phys Anthropol 160:367-378, 2016. © 2016 Wiley Periodicals, Inc.

Aspects of human physical and behavioural evolution during the last 1 million years

“…One such adaptation is the move towards an increasingly meat‐rich diet in later species of Homo . It has been suggested that the barrel‐shaped thorax of Neanderthals evolved to accommodate the necessary increase in liver size and urinary system size for a species that may have been reliant on a diet of up to 85% animal fat during glacial winters (Ben‐Dor et al ., ). This complements the theory discussed earlier that Neanderthal morphologies were adapted to encourage heat production, as studies have indicated that a high protein diet considerably increases heat production from metabolism (Snodgrass and Leonard, ).…”

Ribcage measurements indicate greater lung capacity in Neanderthals and Lower Pleistocene hominins compared to modern humans

“…That large DEE must be caused for their large brains (Fig. 3, Table 3) and large lean body mass (Table 3), but alternative explanations such as the possibility that Neanderthals had large guts (liver and urinary systems) necessary for processing large amounts of meat, could also be linked with high DEE 52 .

Fig. 3 a Thorax and lungs' shape in the frontal view in modern humans and Neanderthals and their associated brains in the lateral view.

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Elephant and Mammoth Hunting during the Paleolithic: A Review of the Relevant Archaeological, Ethnographic and Ethno-Historical Records

“…As at least some of the items mentioned in the data provided above were also manufactured and used by prehistoric groups (e.g., spears and projectiles), and given the technological and cognitive abilities attributed to Lower and Middle Paleolithic populations, and as the profits which could have been yielded from an elephant carcass were abundant and significant, we strongly believe that at least some of the above-presented strategies were also applied by prehistoric people. Furthermore, although some claim that the hunting of large-sized prey was too costly in terms of cost-benefit, compared to that of small game, making such large prey "inefficient choices" [8], it is our contention that elephants played a main role in the Paleolithic diet, providing an abundant supply of meat and fat, in a way unparalleled by any other prey [16], and, hence, were hunted and procured when available and needed.…”