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A Comparative Approach for Quantitative Cell Counting Studies in Widely Different Mammalian Brains
Published on: January 16, 2026
Bigger is not always better: when brains get smaller.
Kamran Safi1, Marc A Seid, Dina K N Dechmann
1Zoologisches Institut, Universität Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland. k.safi@zool.unizh.ch
Biology Letters
|December 7, 2006
Summary
Brain size evolution is complex. Natural selection can reduce brain size when costs outweigh benefits, as seen in fast-flying bats, or increase it for maneuverability in complex environments.
Area of Science:
- Evolutionary biology
- Comparative neuroanatomy
Background:
- Increased brain size is often assumed to be advantageous.
- High metabolic costs are associated with brain production and maintenance.
- Natural selection may favor reduced brain size when costs exceed benefits.
Purpose of the Study:
- To investigate the role of natural selection in regulating brain size.
- To examine whether brain size is subject to bidirectional selection pressures.
- To understand the evolutionary dynamics of brain size reduction and enlargement.
Main Methods:
- Comparative analysis of brain size in bats.
- Correlation of brain size with flight speed and habitat complexity.
- Reconstruction of ancestral brain size states.
Main Results:
- Bat brain size is under bidirectional selection.
- Fast-flying bats show reduced brain size relative to ancestral states.
- Maneuverable bats in complex habitats exhibit increased brain size.
Conclusions:
- Brain size evolution is not solely driven by an increase.
- Natural selection actively shapes brain size through both reduction and enlargement.
- Both brain reduction and enlargement are critical factors in evolutionary studies.
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