Anecdotally, it has seemed to me for a while that Latter-day Saint families in particular tend to have a lot of gay family members. I don’t know of any hard data that has done any kind of comparison-of-means by religion (the sample size would have to be huge, since we’re dealing with a minority within a minority), and I generally assume this perception of mine has to do with the fact that I’m a Latter-day Saint that has done research on sexuality issues, and hammers and nails and all that. However, lately I’ve wondered if we could theoretically expect more homosexuality in Latter-day Saint families because of our larger family sizes.
Why would family size matter? One of the more idiosyncratic findings in human sexuality in the past several decades is that the number of older brothers one has is strongly correlated with male homosexuality (as far as I know there are no established biological correlates of female homosexuality). There are a variety of speculative embryological explanations that have been proffered, but it’s still unclear why this pattern exists. According to some estimates, about 15-30% of gay men owe their homosexuality to this effect.
Anecdotally, the gay men in my life almost all tend to have a lot of older brothers. More rigorously, large studies suggest that every additional brother increases the chance of male homosexuality by about a third. In the data used to derive the “fraternal birth order effect,” any given man without any older brothers has about a 2% chance of being gay (as a sidebar, occasionally I teach a college course, and a fun thing I do is ask for estimates about what percent of people are exclusively gay. After the class inevitability gives estimates of 25-40% I surprise them by telling them that it’s actually 1-3%).
Given this rate, below is the approximate probability of being gay for a male with N older brothers.
This is the chance for any particular male at a certain parity being gay. If we do the same chart, but now for the chance of having at least one gay son in a family of N+1 boys, we have:
[Note, an earlier version of this chart was slightly off but was helpfully corrected by the commenters below]
In other words, a family of 8 boys has a 43% chance of having at least one gay son. (I admit to a little personal curiosity here since we recently discovered we will be blessed with a seventh son), whereas a more standard American family of one boy only has a 2% chance of having a gay son. I won’t attempt to estimate what this means for overall probabilities, since the family size differences between Latter-day Saints and normies varies between time and space, but for the stereotypical large Latter-day Saint families their chances are much higher, both because there are simply more draws, and because the chance of a gay family member with each draw are higher. So in conclusion, because Latter-day Saints have larger families, and larger families mean more older brothers, and older brothers increases the chances of a son being gay, logically men raised in Latter-day Saint homes are in fact more likely to be gay. Additionally, since the larger families tend to be the more conservative ones, ironically the more conservative families are probably more likely to have gay children.
Finally, another interesting implication of all this is that as family sizes decrease and older brothers become more rare, exclusive male homosexuality in the population at large will decrease as well.