Re: Sex Differences In The Brain

Posted by Thermus aquaticus on May 22, 2002 at 00:25

Re: Sex Differences In The Brain (Natalie L. Smith)

Do a search for Falk (a University At Albany anthropologist and an internationally recognized expert in the field of human brain evolution) in the Journal of Human Evolution. She has been examining the evolutionary implications of different brain sizes in men and women. Her work is published. She has tackled the question of whether men have larger brains than women.

Do men have bigger brains than women? Dr Falk says yes. Using casts of the insides of the brain case, called endocasts, and sophisticated computer imaging to produce three-dimensional models of the cranium (virtual endocasts), Falk has determined that men around the world do have bigger brains than women after body size is taken into account. But what does this mean? Falk points out that male rhesus monkeys also have bigger brains than female rhesus monkeys. Whatever males are using their extra neurons for, she says, it's not the higher cognitive abilities - like abstract thinking, judgment and reasoning - that separate us from the monkeys and make us distinctly human. Falk hypothesizes that men's larger brain sizes are probably largely a reflection of the different ways in which men process visual stimuli and construct mental maps of their environment.

Do males need better visual processing? This is the case for certain rodents, known as voles, in which males travel widely to find mates during the mating season. Rhesus monkey males migrate to new social groups when they reach sexual maturity and presumably need keen visual and spatial abilities to do so. So too might have the ancestors of humans, Falk hypothesizes. In a few rare species of Old World monkeys, females, rather than males, do the migrating. Falk is beginning to study brain size of these female monkeys, and how they compare to those of males of the same body size that do not migrate.

Evidence for this hypothesis is that there are sex differences in favour of males in performance in cognitive tests that feature visuospatial tasks such as mental rotation of figures, map-reading, rod-and-frame tests, remembering positions of numbers, left-right discriminations, disembedding figures and localizing points. If the evolutionary hypothesis is correct, further cognitive testing of rhesus monkeys should reveal significant sex differences in the processing of visuospatial information.

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