The 81st Annual Meeting of the American Association of Physical Anthropologists (2012)

Evolution of human encephalization: evidence from a comparative analysis of brain size and fat storage


Anthropological Institute and Museum, University of Zurich

Thursday 3:45-4:00, Broadway III/IV Add to calendar

The human brain stands out among other mammals by being unusually large and energetically expensive. One of the most prominent hypotheses explaining its evolution is the Expensive Tissue Hypothesis (ETH), which proposed a trade-off between brain size and the size of the digestive tract. However, using a newly compiled sample of organ masses and associated brain size from 100 mammalian species, including 23 primate species, we show that the ETH, and any other potential trade-off between brain size and expensive visceral organs, is refuted in both primates and in mammals in general. Nonetheless, we find evidence of energy constraints on brain size evolution, as brain size and the amount of adipose depots are negatively correlated in mammals (N=100, β=-0.07, P=0.017), suggesting that encephalization and fat storage are compensatory strategies to buffer against starvation. We assume that these two strategies can be combined if fat storage does not overly hamper locomotor efficiency. We propose that human encephalization was made possible by a combination of stabilization of energy inputs and redirection of energy from locomotion, growth and reproduction.

This study was funded by the Swiss National Science Foundation grant 3100A0 –117789, with additional support from Synthesis and the A. H. Schultz Foundation.

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