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Brain size and social complexity: a computed tomography study in Hyaenidae.

Sharleen T Sakai¹, Bradley M Arsznov, Barbara L Lundrigan

¹Department of Psychology, Michigan State University, East Lansing, MI, USA. Sakai@msu.edu

Brain, Behavior and Evolution

|February 22, 2011

Summary

The social brain hypothesis suggests complex social lives drive brain evolution. In hyenas, the most social species, the spotted hyena, has a larger brain and frontal cortex, supporting this idea.

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Area of Science:

Comparative neuroanatomy
Evolutionary biology
Behavioral ecology

Background:

The social brain hypothesis links complex sociality to brain expansion.
Evidence primarily comes from primate studies.
Testing this in non-primate species is crucial.

Purpose of the Study:

To investigate the social brain hypothesis in the Hyaenidae family.
To correlate social complexity with relative brain size and anterior cerebrum volume in hyenas.

Main Methods:

Computed tomography was used to create 3D endocasts of hyena skulls.
Analysis focused on relative brain volume and anterior cerebrum volume.
Four species with varying social structures were examined: aardwolf, striped hyena, brown hyena, and spotted hyena.

Main Results:

The spotted hyena (Crocuta crocuta), the most social species, exhibited the largest brain volume relative to body size.
No significant differences in relative brain volume were found among aardwolves, striped hyenas, and brown hyenas.
The spotted hyena showed a proportionally larger anterior cerebrum (frontal cortex) compared to other species.

Conclusions:

Findings support the social brain hypothesis, suggesting that complex social environments may drive brain expansion, particularly in areas like the frontal cortex.
The evolution of large brains in hyaenids may be influenced by social complexity, though other factors could also play a role.