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.
This is a preview of subscription content, log in to check access.
Buy single article
Instant access to the full article PDF.
Price includes VAT for USA
Subscribe to journal
Immediate online access to all issues from 2019. Subscription will auto renew annually.
This is the net price. Taxes to be calculated in checkout.
Aiello, L. C., & Wheeler, P. (1995). The expensive-tissue hypothesis: the brain and digestive system in human and primate evolution. Current Anthropology, 36, 199–221.
Alexander, R. D. (1989). Evolution of the human psyche. In P. Mellars, & C. Stringer (Eds.), The human revolution: Behavioural and biological perspectives on the origins of modern humans (pp. 455–513). Princeton, NJ: Princeton University Press.
Ash, J., & Gallup Jr., G. G. (2007). Paleoclimatic variation and brain expansion during human evolution. Human Nature, 18, 109–124.
Barton, R. A. (1996). Neocortex size and behavioural ecology in primates. Proceedings of the Royal Society of London B, 263, 173–177.
Beaver, P. C., Jung, R. C., & Cupp, E. W. (1984). Clinical Parasitology. Philadelphia, PA: Lea and Febinger.
Brace, C. L. (1995). Biocultural interaction and the mechanism of mosaic evolution in the emergence of “modern” morphology. American Anthropologist, 97, 711–721.
Brothers, L. (1990). The social brain: a project for integrating primate behavior and neurophysiology in a new domain. Concepts in Neuroscience, 1, 27–51.
Colorado State University, Leprosy Research Support (2005). Global Leprosy Map. Available online at http://www.cvmbs.colostate.edu/mip/leprosy/largemap.html.
Dunbar, R. I. M. (1998). The social brain hypothesis. Evolutionary Anthropology, 6, 178–190.
Dunbar, R. (2003). Evolution of the social brain. Science, 302, 1160–1161.
Falk, D. (1983). Cerebral cortices of East African early hominids. Science, 221, 1072–1074.
Flinn, M. V., Geary, D. C., & Ward, C. V. (2005). Ecological dominance, social competition, and coalitionary arms races: why humans evolved extraordinary intelligence. Evolution and Human Behavior, 26, 10–46.
Foley, R., & Lahr, M. M. (1997). Mode 3 technologies and the evolution of modern humans. Cambridge Archaeology Journal, 7, 3–36.
Fox, J., & Monette, G. (1992). Generalized collinearity diagnostics. JASA, 87, 178–183.
Gavrilets, S., & Vose, A. (2006). The dynamics of Machiavellian intelligence. Proceedings of the National Academy of Sciences USA, 103, 16823–16828.
Geary, D. C. (2005). The origin of mind: Evolution of brain, cognition, and general intelligence. Washington, DC: American Psychological Association.
Hill, K., Boesch, C., Goodall, J., Pusey, A., Williams, J., & Wrangham, R. (2001). Mortality rates among wild chimpanzees. Journal of Human Evolution, 40, 437–450.
Holloway Jr., R. L. (1967). The evolution of the human brain: Some notes toward a synthesis between neural structure and the evolution of complex behavior. General Systems, 12, 3–19.
Holloway, R. L. (1975). The role of human social Behavior in the Evolution of the Brain. The 43rd James Arthur Lecture on the evolution of the human brain at the American Museum of Natural History, 1973. New York: American Museum of Natural History.
Holloway, R. L., & de la Coste-Lareymondie, M. C. (1982). Brain endocast asymmetry in pongids and hominids: some preliminary findings on the paleontology of cerebral dominance. American Journal of Physical Anthropology, 58, 101–110.
Holloway, R. L., Broadfield, D. C., & Yuan, M. S. (2004). The human fossil record, Vol. 3: Brain endocasts—The paleoneurological record. Hoboken, NJ: Wiley.
Humphrey, N. K. (1976). The social function of intellect. In P. P. G. Bateson, & R. A. Hinde (Eds.), Growing points in ethology (pp. 303–317). New York: Cambridge University Press.
Ihaka, R., & Gentleman, R. (1996). R: a language for data analysis and graphics. Journal of Computational and Graphical Statistics, 5, 299–314.
Jerison, H. J. (1973). Evolution of the brain and intelligence. New York: Academic Press.
Jolly, C. J. (1970). The seed eaters: a new model of hominid differentiation based on a baboon analogy. Man, 5, 5–26.
Kanazawa, S. (2008). Temperature and evolutionary novelty as forces behind the evolution of general intelligence. Intelligence, 36, 99–108.
Kaplan, H., Hill, K., Lancaster, J., & Hurtado, A. M. (2000). A theory of human life history evolution: diet, intelligence, and longevity. Evolutionary Anthropology, 9, 156–185.
Li, J. Z., Absher, D. M., Tang, H., Southwick, A. M., Castro, A. M., Ramachandran, S., et al. (2008). Worldwide human relationships inferred from genome-wide patterns of variation. Science, 319, 1100–1104.
Low, B. S. (1990). Marriage systems and pathogen stress in human societies. American Zoologist, 30, 325–339.
Malthus, T. R. (1798). An essay on the principle of population as it affects the future improvement of society with remarks on the speculations of Mr. Godwin, M. Condorcet, and other writers. London: Printed for J. Johnson, in St. Paul’s Church-yard.
Marlow, J. R., Lange, C. B., Wefer, G., & Rosell-Melé, A. (2000). Upwelling intensification as part of the Pliocene-Pleistocene climate transition. Science, 290, 2288–2291.
Matarese, G., & La Cava, A. (2004). The intricate interface between immune system and metabolism. Trends in Immunology, 25, 193–200.
McHenry, H. M. (1994). Tempo and mode in human evolution. Proceedings of the National Academy of Sciences USA, 91, 6780–6786.
Noone, D., & Simmonds, I. (2002). Association between δ18O of water and climate parameters in a simulation of atmospheric circulation for 1979–95. Journal of Climate, 15, 3150–3169.
Potts, R. (1998). Variability selection in hominid evolution. Evolutionary Anthropology, 7, 81–96.
Ruff, C. B., Trinkaus, E., & Holliday, T. W. (1997). Body mass and encephalization in Pleistocene Homo. Nature, 387, 173–176.
Satellite Signals. (2007). Latitude and longitude. Retrieved from http://www.satsig.net/maps/lat-long-finder.htm
Shackleton, N. J., Berger, A., & Peltier, W. R. (1990). An alternative astronomical calibration of the lower Pleistocene timescale based on ODP site 677. Transactions of the Royal Society of Edinburgh: Geological Sciences, 81, 251–261.
Tobias, P. V. (1987). The brain of Homo habilis: a new level of organization in cerebral evolution. Journal of Human Evolution, 16, 741–761.
Vrba, E. S. (1974). Chronological and ecological implications of the fossil Bovidae at the Sterkfontein Australopithecine site. Nature, 250, 19–23.
Wood, B., & Collard, M. (1999). The human genus. Science, 284, 65–71.
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.
Electronic supplementary material
Below is the link to the supplementary material
(PDF 60.0 KB)
About this article
Cite this article
Bailey, D.H., Geary, D.C. Hominid Brain Evolution. Hum Nat 20, 67–79 (2009). https://doi.org/10.1007/s12110-008-9054-0
- Cranial capacity
- Ecological dominance
- Parasite prevalence
- Paleoclimatic variability
- Social brain