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Related Experiment Video

Updated: Jun 17, 2026

Assessing Differences in Sperm Competitive Ability in Drosophila

Assessing Differences in Sperm Competitive Ability in Drosophila

Published on: August 22, 2013

Sperm competition and brain size evolution in mammals.

J-F Lemaître¹, S A Ramm, R A Barton

¹Mammalian Behaviour & Evolution Group, Faculty of Veterinary Science, University of Liverpool, Neston, UK. jean-francois.lemaitre@liv.ac.uk

Journal of Evolutionary Biology

|January 14, 2010

Summary

The expensive sexual tissue hypothesis, which links larger testes to smaller brains, is not supported in most mammals. Brain and testis size do not generally trade-off, challenging this evolutionary theory.

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Area of Science:

Evolutionary biology
Comparative anatomy
Neuroscience

Background:

The expensive tissue hypothesis proposes a trade-off between energetically costly organs, like the brain.
The expensive sexual tissue hypothesis specifically suggests larger testes constrain brain size due to sperm competition.

Purpose of the Study:

To test the evolutionary trade-off between brain and testis mass across diverse mammalian groups.
To determine if sperm competition, indicated by mating systems, influences brain size evolution.

Main Methods:

Comparative analysis of brain and testis mass across various mammalian orders (rodents, ungulates, primates, carnivores).
Statistical examination of the relationship between brain mass and mating systems to infer sperm competition levels.
Focused analysis on echolocating bats to investigate specific group dynamics.

Main Results:

No general negative evolutionary trade-off between brain and testis mass was found in mammals.
Brain mass did not significantly vary with mating systems across most mammalian orders.
A negative relationship was observed in echolocating bats, but mating systems appeared to be a stronger predictor of brain size in this group.

Conclusions:

The expensive sexual tissue hypothesis explains little to none of the variation in mammalian brain size.
Broader evolutionary frameworks are needed to understand the energetic costs and constraints of brain evolution.