MU research study picked up by national network

The study looked at what causes changes in brain size.

By Margaux Henquinet

Published July 8, 2009

A recently published study conducted by psychological sciences professor David Geary and graduate student Drew Bailey at MU attracted national attention, landing a spot on CBS's national news Web site June 24.

The two MU researchers spent roughly a year examining 153 hominid skulls in an effort to explain why human brains have grown in size over the past 2 million years.

Geary and Bailey took data from several studies and analyzed it to test what Geary identified as the three main hypotheses for why human brains have grown: to predict and prepare for climate change, to get resources from diverse ecologies or to deal with social competition.

Geary said they looked at different aspects of the region where each skull was found to test each hypothesis, using temperatures to examine climate, evidence of different parasites to represent ecological diversity and population density to judge how competitive the environment would have been.

"We found that all of these variables are mathematically related to the cranium size, but that the population density predicts (skull size) most accurately by far," Bailey said.

Geary said the effects on skulls from population density were four to five times larger than the effects from climate.

"The more individuals that were around in a particular region, the more likely you were to find larger than average brain sizes," Geary said.

Brains grew in size to deal with the complexities of social relationships and cooperation, but also competition, Geary said.

"As the competition becomes more intense, you would expect that individuals with better social skills, such as how to maneuver and get control of those resources, should be at an advantage," Geary said. "If that's the case, we should find that as population increases, brain sizes should increase."

Geary said the idea for the study began when he read a paper published by Gordon Gallup, a professor of evolutionary psychology at the State University of New York at Albany.

Gallup studied changes in cranial capacity and found a strong correlation with changes in temperature -- as global temperatures cooled, brains grew in size.

Additionally, he found the further north or south of the equator the skull was found, the bigger the brains were.

"For each degree of latitude displacement from the equator, there was over an 8 cubic centimeter increase in brain volume," Gallup said.

After reading Gallup's paper, Geary took exception to the idea that climate is what stimulated bigger human brains and went to look at other factors.

Gallup sent Geary and Bailey his data and they reanalyzed it, along with other data, to conduct their own study.

"(It's a) textbook example of how science proceeds," Gallup said. "The findings in one study stimulate people to do other studies and that enlarges and expands what we know about different topics."

After concluding their research, Geary and Bailey published their findings in the Journal of Human Nature. The MU News Bureau wrote a news release on the study, and from there it was picked up by CBS.

"I'm happy that this finding is getting attention because I think that it's an interesting one, and I hope it inspires people to retest this hypothesis," Bailey said. "Whether they find the same thing or something different from us, I'll be glad that it will have encouraged people to do that."