Head Size and IQ: Is There a Link?

Sept. 24, 2007 — Big-headed people could be brainier too, according to a new analysis of a 1939 study comparing head size and intelligence in a group of male prisoners.

Although the effect of head size on IQ is minimal, it does exist, says Jeremy Genovese, who conducted the new research and is an associate professor of human development and educational psychology at Cleveland State University.

"The correlations between head size and IQ are quite modest, and you cannot determine someone's intelligence with a tape measure," he told Discovery News. "However, the correlation is real and might have some clinical significance, such as predicting susceptibility to dementia."

Genovese explained that "larger bodies do require larger brains to support larger nervous systems," but he added that the notable difference in body size between men and women appears to have "no relationship to intelligence."

For the study, which has been accepted for publication in the journal Personality and Individual Differences, Genovese obtained copies of the 1939 inmate data, which was collected by Harvard anthropologist Earnest Albert Hooten. Hooten gathered anthropological and sociological records on roughly 12 percent of American prison inmates.

Included in Hooten's study were head size measurements of 676 male inmates at the Concord Reformatory in Massachusetts, since IQ tests had already been performed on the same prisoners. Hooten documented head circumference, head length, head height and even head shape.

Genovese used statistical computer software to find patterns hidden from Hooten, considering the more limited methods of his day.

Other scientists have linked head shape to higher IQs, arguing that a rounder head is associated with greater intelligence, but Genovese could find no such link. He was, however, able to confirm what Hooten suggested, that there is a connection between head size and intelligence. But teasing out that connection is anything but simple.