University of Kentucky

Poster Title

The Relationship Between Brain Size and Muscle Mass Among Primates

Institution

University of Kentucky

Abstract

Primates have larger brains than most other mammals, yet they do not have significantly higher metabolic costs. In other words, although the brain tissue needs more energy to function the overall energy needs of large brain primates do not increase significantly when compared to small-brained animals of a similar size. There have been a number of proposed theories to help clarify this phenomenon. The Expensive Tissue Hypothesis suggests that primates are offsetting the energetic demands of a large brain by reducing the size of other metabolically expensive tissues (e.g., the gut). Brain/tissue tradeoffs have been studied in depth with many organs however, little attention has been given to skeletal muscle. Skeletal muscle has exceptionally high metabolic requirements when active, higher than most other organ systems. To evaluate if there was an energy tradeoff between brain and skeletal muscle, we dissected and obtained muscle mass weights from 15 primates species. We then collected endocranial volumes (a measure of brain size) from the literature. We found a significant negative correlation between relative endocranial volumes and muscle mass. This study will allow evolutionary biologists to better understand how primates and humans can sustain a relatively large brain, without additional metabolic requirements. This is just the first phase of a long-term study that will evaluate the relationship between muscle fiber composition, growth and development, brain enlargement and human health (e.g. diabetes and obesity).

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The Relationship Between Brain Size and Muscle Mass Among Primates

Primates have larger brains than most other mammals, yet they do not have significantly higher metabolic costs. In other words, although the brain tissue needs more energy to function the overall energy needs of large brain primates do not increase significantly when compared to small-brained animals of a similar size. There have been a number of proposed theories to help clarify this phenomenon. The Expensive Tissue Hypothesis suggests that primates are offsetting the energetic demands of a large brain by reducing the size of other metabolically expensive tissues (e.g., the gut). Brain/tissue tradeoffs have been studied in depth with many organs however, little attention has been given to skeletal muscle. Skeletal muscle has exceptionally high metabolic requirements when active, higher than most other organ systems. To evaluate if there was an energy tradeoff between brain and skeletal muscle, we dissected and obtained muscle mass weights from 15 primates species. We then collected endocranial volumes (a measure of brain size) from the literature. We found a significant negative correlation between relative endocranial volumes and muscle mass. This study will allow evolutionary biologists to better understand how primates and humans can sustain a relatively large brain, without additional metabolic requirements. This is just the first phase of a long-term study that will evaluate the relationship between muscle fiber composition, growth and development, brain enlargement and human health (e.g. diabetes and obesity).