Fetus Brain Development

In The Female Brain, Louann Brizendine claims that all baby brains start out female - but then in a male brain along comes that nasty hormone Testosterone, and it begins to damage the brain. It then "turns" the brain into a male brain by chipping away at its full functionality.

Unfortunately, research does not show this to be true. All baby brains start out NEUTRAL, in a blank state stage. Studies with mice (since it's generally unethical to experiment with human embryos ;) ) show that there are already changes happening in the fetal brain BEFORE the testes are forming, before hormones are flowing.

To learn more about this path, here's a 2004 article on Nature, on brain development:

Nature - Brain Development

A gene "Sry" on males (the Y chromosome) begins testes growing, which then sends out the male hormones. Researchers used to think that Sry alone was in charge of everything. That men who had Sry removed "stayed" female - and that females who had Sry added "turned" male. However, that's not the whole story. Research has shown that other factors are involved.

A key result of this is transsexualism - people who are physically one sex but mentally the other.

In another interesting study in Endojournals.org -

Endojournals - Transsexuals

"The number of neurons in the BSTc of male-to-female transsexuals was similar to that of females (19.6 3.3 x 103) (P = 0.83)"

The Female Brain - Louann Brizendine

Lisa's Biology Pages