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Decreases in Brain Size and Encephalization in Anatomically Modern Humans
1Natural History Museum, Los Angeles, California, USA.
Brain, Behavior and Evolution
|October 31, 2021
Summary
Human brain size and encephalization have decreased over the last 50,000 years. Declines in encephalization are linked to increased obesity, not just evolutionary changes in brain mass.
Area of Science:
- Human Evolution
- Paleoanthropology
- Neuroscience
Background:
- Human brain size and encephalization are linked to cognitive abilities.
- Recent millennia show a decrease in human body and brain size.
- The relationship between these changes and encephalization is not well understood.
Purpose of the Study:
- To examine changes in human brain size and encephalization.
- To analyze the scaling relationship between brain size and body mass over evolutionary time.
- To investigate the impact of recent obesity on encephalization.
Main Methods:
- Analysis of matched human body and brain remains across evolutionary periods.
- Calculation of encephalization levels in ancient and modern Homo sapiens.
- Meta-review of genome-wide association studies on cognitive ability.
Main Results:
- Modern humans exhibit decreased encephalization compared to earlier Holocene and Late Pleistocene Homo sapiens.
- When controlling for lean body mass, encephalization changes are isometric.
- Recent increases in obesity appear to be a primary driver of observed encephalization declines.
- Evidence suggests selective pressures on human cognitive ability may be linked to brain mass loss.
Conclusions:
- Observed decreases in human encephalization are significantly influenced by recent increases in obesity.
- Evolutionary pressures may have acted on cognitive abilities due to a notable loss in brain mass over the past 50,000 years.
- Further research is needed to fully understand the complex interplay between body mass, obesity, and human brain evolution.
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