Selection for smaller brains in Holocene human evolution

TL;DR

This study investigates the recent reduction in human brain size during the Holocene, finding evidence that it resulted from direct selection on brain size rather than just correlated body size changes.

Contribution

It provides evidence that brain size reduction in Holocene humans was driven by selection on brain size itself, not solely by genetic correlation with body size.

Findings

Absolute brain size decrease exceeded predictions from body size changes

Selection likely targeted brain size directly or features highly correlated with it

Possible influences include energetic, nutritional, or life history factors

Abstract

Background: Human populations during the last 10,000 years have undergone rapid decreases in average brain size as measured by endocranial volume or as estimated from linear measurements of the cranium. A null hypothesis to explain the evolution of brain size is that reductions result from genetic correlation of brain size with body mass or stature. Results: The absolute change of endocranial volume in the study samples was significantly greater than would be predicted from observed changes in body mass or stature. Conclusions: The evolution of smaller brains in many recent human populations must have resulted from selection upon brain size itself or on other features more highly correlated with brain size than are gross body dimensions. This selection may have resulted from energetic or nutritional demands in Holocene populations, or to life history constraints on brain development.