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A Comparative Approach for Quantitative Cell Counting Studies in Widely Different Mammalian Brains
Published on: January 16, 2026
Energetics and the evolution of human brain size
Ana Navarrete1, Carel P van Schaik, Karin Isler
1Anthropological Institute and Museum, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland. a.navarrete@aim.uzh.ch
Nature
|November 15, 2011
Summary
The expensive-tissue hypothesis is refuted; brain size is not linked to digestive tract size in mammals. Instead, brain size and fat storage show a negative correlation, suggesting compensatory strategies for energy conservation.
Area of Science:
- Evolutionary Biology
- Comparative Anatomy
- Neuroscience
Background:
- The human brain's large size is a distinctive mammalian trait.
- The expensive-tissue hypothesis posits a trade-off between brain size and digestive tract size.
- Empirical evidence for this hypothesis has been inconsistent.
Purpose of the Study:
- To empirically test the expensive-tissue hypothesis across mammalian species.
- To investigate the relationship between brain size and other organ masses, particularly the digestive tract.
- To explore energy trade-offs related to brain evolution.
Main Methods:
- Analysis of brain size and organ mass data from 100 mammalian species, including 23 primates.
- Statistical control for fat-free body mass to isolate organ size correlations.
- Comparative analysis of encephalization and organ mass.
Main Results:
- Brain size showed no negative correlation with digestive tract mass or other energetically expensive organs, refuting the expensive-tissue hypothesis.
- A negative correlation was found between brain size and adipose depots (fat storage) across mammals.
- Encephalization and fat storage appear to be compensatory strategies for starvation resistance.
Conclusions:
- The expensive-tissue hypothesis is not supported by this comparative analysis.
- Mammalian brain evolution may involve trade-offs with energy storage (fat) rather than digestive organ size.
- Human encephalization likely resulted from stabilized energy intake and reallocation from other functions like locomotion.
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