Sex differences in human brain size and the general meaning of differences in brain size.

Abstract

Contrary to commonly held convictions, there is no clear association between brain size and body parameters in humans. Within sexes, once age and health status are controlled for, there is no significant association between brain size and body height for females. For males, body height accounts for no more than .04% of the variance in brain size. The relation between brain weight and body weight is even less clearly defined. Nevertheless, there are large and significant differences in brain size between the sexes. If no adequate body parameters can be found that scale to brain size within the sexes, the marked dimorphism between males and females makes it even more difficult to find a common set of parameters that allow evaluation of brain size differences between sexes. Within and across sexes, there is no convincing link between a limited measure of behavioural capacity (IQ) and brain size. This leads to the more general question: Why would one expect such a link, and, if it is not found, what does this mean in the context of general theories of cortical function?