Human Nature

, Volume 18, Issue 2, pp 109–124

Paleoclimatic Variation and Brain Expansion during Human Evolution


DOI: 10.1007/s12110-007-9015-z

Cite this article as:
Ash, J. & Gallup, G.G. Hum Nat (2007) 18: 109. doi:10.1007/s12110-007-9015-z


One of the major adaptations during the evolution of Homo sapiens was an increase in brain size. Here we present evidence that a significant and substantial proportion of variation in brain size may be related to changes in temperature. Based on a sample of 109 fossilized hominid skulls, we found that cranial capacities were highly correlated with paleoclimatic changes in temperature, as indexed by oxygen isotope data and sea-surface temperature. Indeed, as much as 52% of the variance in the cranial capacity of these skulls could be accounted for by temperature variation at 100 ka intervals. As an index of more short-term seasonal fluctuations in temperature, we examined the latitude of the sites from which the crania originated. More than 22% of the variance in cranial capacity of these skulls could be accounted for by variation in equatorial distance.


Cranial capacityHomoPaleoclimatic variabilitySeasonal variabilitySea-surface temperatureVariability selection

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© Springer Science & Business Media, LLC 2007

Authors and Affiliations

  1. 1.Department of PsychologyUniversity at Albany, State University of New YorkAlbanyUSA