Decreases in Brain Size and Encephalization in Anatomically Modern Humans

doi:10.1159/000519504

Paper

Decreases in Brain Size and Encephalization in Anatomically Modern Humans

Published Oct 29, 2021 · Jeffrey M. Stibel

Brain, Behavior and Evolution

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11

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2

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Abstract

Growth in human brain size and encephalization is well documented throughout much of prehistory and believed to be responsible for increasing cognitive faculties. Over the past 50,000 years, however, both body size and brain mass have decreased but little is known about the scaling relationship between the two. Here, changes to the human brain are examined using matched body remains to determine encephalization levels across an evolutionary timespan. The results find decreases to encephalization levels in modern humans as compared to earlier Holocene H. sapiens and Late Pleistocene anatomically modern Homo. When controlled for lean body mass, encephalization changes are isometric, suggesting that much of the declines in encephalization are driven by recent increases in obesity. A meta-review of genome-wide association studies finds some evidence for selective pressures acting on human cognitive ability, which may be an evolutionary consequence of the more than 5% loss in brain mass over the past 50,000 years.

Meta-Analysis

Study Snapshot

Key takeawayModern humans have experienced a decrease in brain size and encephalization, likely driven by increased obesity, potentially impacting cognitive ability and potentially affecting evolutionary processes.

PopulationOlder adults (50-71 years)

Sample size24

MethodsObservational

OutcomesBody Mass Index projections

ResultsSocial networks mitigate obesity in older groups.

Decreases in Brain Size and Encephalization in Anatomically Modern Humans

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