Saturday, July 23, 2011

What makes men gay?

The final top donor request (the rest didn't request a topic):
"blog about this"
Since this is from a friend and not a stranger, I can safely say this: I hate you for making me read a scientific paper and review it during Blogathon. Hate. So much hate.

But you have my word, so I'll do it. Onto the science!

A lot of people like to ask the question "What makes men gay?" It's pretty clear it's not a willy-nilly lifestyle choice, but scientists still aren't really sure what the biology behind homosexuality actually is. Is it genetic? Hormonal?

Research on the latter is what a recent review article in the journal Frontiers in Neuroendocrinology summarized. You probably heard about the starting premise, since it received a lot of attention in the media. A study in 1996 found that gay men had a greater number of older brothers than heterosexual men. This is known as the "fraternal birth order" (FBO) effect, and has been replicated in many studies. It's independent of potentially confounding variables like year of birth, age, socioeconomic status, and parental age. Non-biological siblings had no effect on sexual orientation.

The main hypothesis for why you see this pattern is known as the maternal immune hypothesis. Just like your body mounts an immune response against bacteria or ill-matched transplants, moms may develop an immune reaction against a male specific protein that's present during development. Those proteins are normal for a male fetus, but a mother's body still recognizes them as foreign. The immune response may then alter parts of the brain associated with male specific proteins like the anterior hypothalamus, which has also been linked to sexual orientation.

Recent research is finding more and more support for this hypothesis. One study showed that mothers of boys do develop an immune response to H-Y antigen, which is a protein expressed in the brain that is important in male fetal development. This immune response becomes stronger and stronger with each son a mother has.

This isn't a totally crazy hypothesis. This exact thing happens in terms of blood type:
A medical model for a maternal immune response underlying the FBO effect is Hemolytic Disease of the Newborn (HDN). When a mother does not have the Rh factor in her blood (i.e., a mother is Rh negative), after gestating and giving birth to an Rh positive (Rh +) fetus, she may mount an immune response against the Rh factor. This immune response may affect subsequent Rh + fetuses, potentially attacking their red blood cells and causing anemia. The likelihood of an immune response becomes increasingly likely with each Rh + fetus a mother gestates.
There's a problem though. H-Y antigen isn't just produced in the brain - it's also expressed in the gonads. Homosexual and heterosexual men don't have any major difference in terms of gonads or fertility. Is there a way that the immune response would only effect H-Y proteins in the brain, but not in the gonads?

Possibly. Mice testes can develop without H-Y. And male gonads don't reach maturity until puberty, so maybe a maternal immune response wouldn't affect sperm too much.

The most compelling point is that there are three different forms of H-Y protein. It's possible that the different forms are localized in different tissues, with only the one in the brain being targeted by the maternal immune response. However, there's currently no information on where different forms of H-Y protein are localized.

Despite all of this evidence, this still doesn't provide an actual mechanism. There's a big gap between "increased immune response" to "homosexual behavior." What are all of the steps in between? And is H-Y the only male specific protein that a maternal immune response targets? Probably not, but more research still needs to be done.

So do we definitively know what's going on yet? Not quite. But feel free to slap homophobes with some science the next time you hear "lifestyle choice."

And there goes all of the Blogathoon buffer time I had built up. Curses!

This is post 24 of 49 of Blogathon. Pledge a donation to the Secular Student Alliance here.


  1. I don't understand why some people try hard to demonstrate that gays are just gays, and they have nothing whatsoever to do about it! Poor them, they are just attracted to other men and they can't fight it. they can't prevent themselves from not acting on it. period. Why would they subject themselves to social rejection, and injustice if it were easy to deny being gay!! Well, I don't agree, if this is the case, then...then, we can also rationalize J Sandusky or any pedophile for that matter. Poor him, he is just attracted to young biys, he can't do anything about, and he can;t prevent himslef from acting on it. or, maybe ...incest, the father, is just attracted to his girl...and if she consenting, that s completely ok, actually in some societies, it is. the only difference between gay men and pedophiles is that one has a consenting partner, and the other doesn't (you cant call kids a consenting partner), but the same deviate sexual urge is there. so then , why do we punch pedophile. we can just say that poor them, they can't do anything about it. we do we punish incest? we can rationalize it the same way.  The key here is learned learn to hold yourself from a ceratin behavior, and not act on it because it is wrong. someone would argue that homosexuality is natural. well I argue that it is a matter of fact, there is no natural lubrication available for sodomy! ...there are tons of reason why homosexuality is not normal.

  2. Commenting on the first comment,How can you compare homosexual with pedophile and incest?  it seem that you have not done enough research on the subject (They are not predators)Its sad to think that your opinion is still in the dark ages if you were a parent of a gay person you would not think that way ,we have a long way to go to educate our society

  3. There are also tons of reasons why you're not normal you a***** it's sad ppl like u exist the only evil is u not gay ppl

  4. Homosexuality is normal
    And at least they help population control not like freeloading breeders like you

  5. The only one that isn't normal
    Is you how dare u think u have a right to decide what Ppl are and what they are not you closet homo

  6. You're a pedofile u prob touch you girls
    You straight piece
    Of trash