Hominid Brain Evolution
- 1.6k Downloads
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.
KeywordsHominid 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.
- 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.Google Scholar
- Beaver, P. C., Jung, R. C., & Cupp, E. W. (1984). Clinical Parasitology. Philadelphia, PA: Lea and Febinger.Google Scholar
- Brothers, L. (1990). The social brain: a project for integrating primate behavior and neurophysiology in a new domain. Concepts in Neuroscience, 1, 27–51.Google Scholar
- Colorado State University, Leprosy Research Support (2005). Global Leprosy Map. Available online at http://www.cvmbs.colostate.edu/mip/leprosy/largemap.html.
- Fox, J., & Monette, G. (1992). Generalized collinearity diagnostics. JASA, 87, 178–183.Google Scholar
- 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.Google Scholar
- 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.Google Scholar
- 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.Google Scholar
- Jerison, H. J. (1973). Evolution of the brain and intelligence. New York: Academic Press.Google Scholar
- Low, B. S. (1990). Marriage systems and pathogen stress in human societies. American Zoologist, 30, 325–339.Google Scholar
- 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.Google Scholar
- 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.Google Scholar
- 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.Google Scholar