For those of you over at Basic Rights Oregon, Human Rights Commission, and you Bryan over at Gay Rights Watch who insist that gender is merely an "expression" I would encourage you to read the book Why Gender Matters by Leonard Sax, M.D., Ph.D..
Dr. Sax's source notes are filled with University studies published in reputable medical journals. You can't argue with the science. (well you can but that makes you stupid)
Far from being a right-winger Dr. Sax focuses only on the actual hardwired differences in males and females in everything from how we solve problems, hear, see, relate, etc.
I'm about halfway through the book and while I don't agree with Dr. Sax on things like gender roles (he seems to oppose) and I haven't gotten to his chapter on gays and lesbians (perhaps he will insist that they are "born that way") I am facinated by the real differences in boys and girls.
I couldn't be more sure that children need a mother and a father to raise them. Not two mommies, not two daddies, not a sixteen year old girl.
Get the book, read it.