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


Primates are all brain and little brawn: a preliminary investigation into tissue tradeoffs

MAGDALENA N. MUCHLINSKI1, LISA NEVELL2, RUI DIOGO3 and J JOSH. SNODGRASS4.

1Anatomy and Neurobiology, University of Kentucky, Lexington, 2Department of Human Genetics, University of Utah, 3Department of Anatomy, Howard University College of Medicine, 4Department of Anthropology, University of Oregon, Eugene

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Despite major differences in morphology and ecology, mammalian species have broadly similar metabolic requirements relative to body size. This commonality suggests that the total energy available for meeting the metabolic needs of the various somatic organs and tissues is constrained. Thus, available energy is allocated differentially depending upon the metabolic needs of each species. This is the basis of the Expensive Tissue Hypothesis, which proposes an explanation for how humans are able to maintain large, energy-expensive brains while having resting metabolic rates that are not substantially different from other mammals. Muscle tissue, despite relatively low costs when at rest, requires a substantial portion of overall daily metabolic requirements. Thus, we hypothesize that muscle mass will be lower in primates with relatively large brains. To test this hypothesis, we obtained total muscle mass values via dissection for 12 primate species and combined this information with literature-based data from an additional 11 species. We also compiled muscle mass values from literature sources for 56 non-primate mammals. In addition, endocranial volumes (ECVs) were obtained from the literature for each primate species. We compared primates and non-primate mammals in relative muscularity, and examined how muscle mass covaries with ECV. Results indicate that primates are hypomuscular when compared to non-primate mammals (P<0.001). We also documented a negative correlation between relative muscle mass and relative ECV (P<0.05). This suggests that primates may 'save' energy by reducing muscle mass, which can then be allocated to the brain and other tissues.

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