Jeremy Yoder in Scientific American:
I'm looking forward to celebrating Pride for the first time in my new hometown of Minneapolis this weekend–but as an evolutionary biologist, I suspect I have a perspective on the life and history of sexual minorities that many of my fellow partiers don't. In spite of the progress that LGBT folks have made, and seem likely to continue to make, towards legal equality, there's a popular perception that we can never really achieve biological equality. This is because same-sex sexual activity is inherently not reproductive sex. To put it baldly, as the idea is usually expressed, natural selection should be against men who want to have sex with other men–because we aren't interested in the kind of sex that makes babies. An oft-cited estimate from 1981 is that gay men have about 80 percent fewer children than straight men.
Focusing on the selective benefit or detriment associated with particular human traits and behaviors gets my scientific dander up, because it's so easy for the discussion to slip from what is “selectively beneficial” to what is “right.” A superficial understanding of what natural selection favors or doesn't favor is a horrible standard for making moral judgements. A man could leave behind a lot of children by being a thief, a rapist, and a muderer–but only a sociopath would consider that such behavior was justified by high reproductive fitness.
And yet, as an evolutionary biologist, I have to admit that my sexual orientation is a puzzle.