Testing the expensive-tissue hypothesis' prediction of inter-tissue competition using causal modelling with latent...

Area of Science:

• Human evolution
• Nutritional science
• Neuroscience

Background:

• The expensive-tissue hypothesis (ETH) proposes a trade-off between brain size and other organ investments to explain human brain evolution.
• Previous tests of the ETH have focused on non-human animals, leaving human evidence scarce.

Purpose of the Study:

• To investigate the causal relationship between brain tissue investment and lean/fat body tissue investment in humans.
• To empirically test versions of the expensive-tissue hypothesis in a human cohort.

Main Methods:

• Structural equation modeling with instrumental variables was employed to analyze brain and body composition data from 70 South Asian women.
• This causal inference approach mitigates issues like measurement error, confounding, and reverse causality.

Main Results:

• Negative causal estimates were observed for the relationship between brain tissue investment and lean body tissues (-0.41) and fat tissues (-0.56).
• While the confidence intervals were wide and results inconclusive, the trends align with the ETH's predictions of a brain-body trade-off.

Conclusions:

• The findings provide preliminary, albeit inconclusive, support for the expensive-tissue hypothesis in humans, suggesting a potential causal trade-off between brain and body tissue investment.
• Further research with larger datasets, genetic data, and advanced causal modeling is needed to solidify these findings and expand the evidence base for the ETH in human evolution.