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Question #89164 posted on 03/27/2017 10:05 a.m.

Dear 100 Hour Board,

I'm gay, so is my brother. We have several cousins who are gay or lesbian or bi (all on one side). Our parents each have a few gay cousins as well. There's reason to believe that there were some closeted gays in our family history, especially on the side that has all the gay cousins.

Other people don't have any gay relatives at all, or very few.

Studies have not yet found a specific gene or genes that explain homosexuality. However, my anecdotal experience suggests that it may run in families. Does it? Also, what are the current theories (accepted by science, the crackpot ones suggested by people threatened by gays seem dubious) about the causes of homosexuality?

-My Name Here


Dear MNH,

Good to hear you have some LGBTQ relatives! Regardless of whether there's a genetic cause for it, that's probably good for support. When my cousin came out as bisexual, I felt a lot less ostracized in the family and able to rely on her as support. Having a brother who knows (at least on some level) what you're going through sounds like a comforting thing.

As for whether it's genetic, anecdotal experience may not be the most reliable factor. It may be that your family just has a lot of LGBTQ relatives, or it could be that for some reason that side of your family is more open to exploring their sexual orientation. That being said, one study has shown that gay males are more likely to have gay male cousins and uncles. This means that in specifically male sexual orientation, some aspects may be genetic. It would need to be studied further and tested with a larger sample size, though, to come to further conclusions.

Some twin studies have attempted to find a link between sexual orientation and genetics. They found that identical and fraternal twins both have an increased rate of sharing a sexual orientation than other siblings, meaning that genetics could play a part but is not the only key. While it may be tempting to want a link between sexual orientation and genetics, this may not be the best thing or even fully correct. Sexual orientation is fluid and can shift in many directions as a person is more open with themselves. Finding a genetic cause for sexual orientation may not even change how people look at sexual orientation, as there would still be those out there viewing it as a medical disorder. 

Some even worry that if there was a pinpointed genetic cause for sexual orientation, mothers would abort unborn babies that showed signs of becoming gay later in life or that doctors would be more likely to develop medical or surgical procedures to "cure" it. It would not necessarily be a good thing, nor would it change how prejudiced people see sexual orientation.

That doesn't mean that sexual orientation is in your control (ie: a choice), though, or that strictly environmental factors cause it. Although researchers are currently unsure what might influence sexual orientation, they do have some theories. It could be that, like many factors that make up a human being, there is no one "cause" but many biological or environmental factors that make a person more likely to develop a certain sexual orientation. Here are a few:

  • Evolutionary factors could also come into play, though these are at best theories. The "gay uncle hypothesis" posits that gay men or women who don't have children may contribute to resources for the offspring of their relatives, increasing the strength of their family genes for future generations. This is, of course, less true in contemporary society as gay couples have many resources if they want to start a family.
  • Prenatal development may be another factor. Hormone exposure in the womb could affect brain development and possibly sexual orientation when exposed to different testosterone levels. Female fetuses exposed to more testosterone during development could be more likely to experience attraction towards other females, and male fetuses exposed to less testosterone may also be more likely to experience attraction towards other males.
  • Females with a gay relative tend to have more offspring than those without gay relatives. This may mean that a similar factor that promotes fertility is linked to sexual orientation. In addition, the way that gay and straight people respond to pheromones of the gender they're attracted to is identical. This means that on a biological level, sexual attraction operates in the same way regardless of orientation.
  • Some studies have found that when it comes to male sexual orientation, a man without older brothers is two percent likely to identify as gay but a man with four older brothers is six percent. This could potentially mean that exposure to certain antibodies in the womb could make a person less likely to be attracted to the same gender, as these antibodies are produced less with every baby. These studies and their result has been called into question, though, so take it at a face value.

Hope this helps! I'm not even going to pretend to know a lot about genetics so take this at a very basic level and do your own research. Again, these are all theories and there is no one known cause of sexual orientation. If any readers have more information about this, feel free to leave a correction.

-Van Goff