Sharon Begley, Newsweek's science editor, has an interesting piece on the Newsweek web site that explains why parents may cause gender differences in their kids and that at birth, there really is no difference in the male and female brains.
You can read the whole piece here.
It makes sense to me.
Dad was absent in my early life working two jobs to support his wife and kids. Mom cherished her firstborn child (me), coddled and pampered me, and instilled in me many traits that were considered "feminine." With Dad absent early-on, Mom was all I had to model myself after and that I did, which just compounded my feminization.
And so it goes.
(The image above is titled The Pink Boy and is Gainsborough's companion piece to his famous painting The Blue Boy.)