Brain heat dissipation patterns in modern humans, fossil hominids and great apes: A comparative study

Maintaining a constant temperature of the brain is a critical issue as slight variations in cerebral temperature may cause irreversible neural damage or even cause death of the individual. From an evolutionary perspective, when compared with other primates the human brain is not only bigger but it also consumes a larger amount of energy. Since brain size is constrained by the ability of an organism to efficiently remove the heat produced by neural metabolism, it has been proposed that brain size increase in humans was possible due to the coevolution of a complex vascular system able to efficiently dissipate heat. Searching for morphological correlates of brain metabolism, we performed numerical simulations to describe and to quantify the heat dissipation patterns within the brain volume as a function of the endocranial geometry in a comparative dataset of living and extinct hominoids. Our results show that brain size relates to general differences in the heat dissipation patterns among species, while thermic mapping evidence discrete differences localized on the parietal lobes, the temporal lobes and the motor cortex. Great apes display relatively high thermic values along this regions, with gorillas showing larger thermal loads than orangutans or chimpanzees. Australopithecines differ from great apes in showing lower loads at the frontal and parietal regions as the result of having taller brains. Extinct humans show a thermic gradient with low temperatures at the temporal lobes and higher values at the fronto-parietal surface related to their wider and flattened brains, while in modern humans this gradient is attenuated by relatively lower thermal loads at the parietal lobes, this being associated with parietal bulging and a more globular brain.

Keywords: brain evolution, hominoids, thermoregulation

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