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You're very kind and I'm honored to be here and honored that you would come to listen.

I'm here by permission from the Department of Microbiology and Molecular Biology and the College of Life Sciences.

That's not to imply any sponsorship. I alone am responsible for what you'll hear tonight and I'm not representing views of BYU or my College or Department.

I think that there are three questions which thoughtful people will inevitably ask about the subject of homosexuality.

They are related to one another and in fact they sit together in a nested set and at the center is the issue of cause.

Even if we were to be able to know everything there is to know about the origin of sexual orientation, it would still be intellectually important and spiritually important for us to ask whether orientation is changeable.

Exploring these two complex issues would naturally lead us to try to understand what it's like to be a gay or lesbian later they say.

Tonight the topic is the first of these the cause of homosexuality.

So let's rephrase the question in these terms. Perhaps most often this issue is reflected in the question.

Do gay and lesbian people choose their orientation?

We're going to begin with a very brief introduction to the topic of human sexual development.

Women have two X chromosomes and those two X chromosomes create a default biological system.

Women's with two X chromosomes develop ovaries and a female brain and that female brain is most often adapted to be attracted erotically and romantically to males.

Boys are different than girls.

Men have a Y chromosome and the Y chromosome changes the default program of human development.

There is a gene on the Y chromosome that has been identified and cloned and its function very well described.

One of its primary consequences is the presence in relatively large quantities of the steroid hormone testosterone.

Sexual orientation is about the programming of the human brain. Testosterone is responsible for that in a complex way.

Sometimes testosterone itself will activate receptors and begin biochemical signaling in the brain.

Sometimes it is converted to a related testosterone-like compound which can do some of that brain programming.

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