Human Nature

, Volume 20, Issue 1, pp 67–79 | Cite as

Hominid Brain Evolution

Testing Climatic, Ecological, and Social Competition Models
  • Drew H. Bailey
  • David C. GearyEmail author


Hypotheses regarding the selective pressures driving the threefold increase in the size of the hominid brain since Homo habilis include climatic conditions, ecological demands, and social competition. We provide a multivariate analysis that enables the simultaneous assessment of variables representing each of these potential selective forces. Data were collated for latitude, prevalence of harmful parasites, mean annual temperature, and variation in annual temperature for the location of 175 hominid crania dating from 1.9 million to 10 thousand years ago. We also included a proxy for population density and two indexes of paleoclimatic variability for the time at which each cranium was discovered. Results revealed independent contributions of population density, variation in paleoclimate, and temperature variation to the prediction of change in hominid cranial capacity (CC). Although the effects of paleoclimatic variability and temperature variation provide support for climatic hypotheses, the proxy for population density predicted more unique variance in CC than all other variables. The pattern suggests multiple pressures drove hominid brain evolution and that the core selective force was social competition.


Hominid Cranial capacity Ecological dominance Parasite prevalence Paleoclimatic variability Social brain 



The authors thank Jessica Ash, Gordon Gallup, Christopher Ruff, and Satoshi Kanazawa for sharing their data and for helpful comments throughout the data collection process; Carol Ward and Deborah Cunningham for their help in the data collection process; Margie Gurwit and Phil Wood for their help with analyses; Mary Hoard, Lara Nugent, and Jon Oxford for their time throughout the project; and Ralph Holloway and two anonymous reviewers for their comments on an earlier draft.

Supplementary material

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Copyright information

© Springer Science + Business Media, LLC 2008

Authors and Affiliations

  1. 1.Department of Psychological SciencesUniversity of MissouriColumbiaUSA

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