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How the Brain May Have Shaped Muscle Anatomy and Physiology: A Preliminary Study
Magdalena N Muchlinski1, Holden W Hemingway1,2, Juan Pastor3
1Center for Anatomical Sciences, University of North Texas, Fort Worth, Texas.
Anatomical Record (Hoboken, N.J. : 2007)
|February 9, 2018
Summary
Larger-brained primates have less muscle mass and fewer Type I muscle fibers. This finding supports the revised expensive tissue hypothesis, linking brain size to reduced muscle energetics in primates.
Area of Science:
- Evolutionary biology
- Comparative anatomy
- Primate evolution
Background:
- Skeletal muscle fiber composition influences locomotion and energetics.
- The expensive tissue hypothesis (ETH) links brain size to other tissue reductions.
- Skeletal muscle is energetically costly and competes with the brain for glucose.
Purpose of the Study:
- To test the hypothesis that larger-brained primates have relatively less muscle mass and fewer Type I fibers.
- To investigate the relationship between brain size, muscle mass, and muscle fiber type in primates.
- To explore the energetic trade-offs between brain and muscle tissues in primate evolution.
Main Methods:
- Collected body mass, muscle mass, and muscle biopsies from 10 primate species.
- Performed histological analysis using immunohistochemistry to profile muscle fiber composition (Type I and Type II).
- Utilized published endocranial volumes for brain size data.
Main Results:
- Larger-brained primate species exhibit significantly less muscle mass compared to smaller-brained species.
- A negative correlation was observed between brain size and the proportion of Type I muscle fibers.
- These results support the hypothesis that brain expansion is associated with reduced muscle mass and specific fiber types.
Conclusions:
- Primate brain size is inversely related to muscle mass and Type I fiber proportion.
- Muscle energetics play a crucial role in evolutionary trade-offs, particularly concerning brain expansion.
- This study provides evidence for the energetic competition between brain and skeletal muscle tissues in primates.
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