Blanchard, Ray; Lippa, Richard A. “The sex ratio of older siblings in non-right-handed homosexual men .” Archives of Sexual Behavior (2006): in press. Abstract available at http://dx.doi.org/10.1007/s10508-006-9107-6.
Recent research that shows a link between male homosexuality and the number of older brothers has gotten a lot of attention lately. For several decades researchers have noticed that gay men are less likely to be among the firstborn, and more specifically they are more likely to have more older brothers than sisters. This phenomenon, generally referred to as the Fraternal Birth Order effect (or sometimes the Sibling Sex Ratio effect), generally holds true for gay men but it but doesn’t hold true for lesbians. Researchers have also noticed that gay men and women are more likely to be left-handed than everyone else. This study tries to look at the interaction of the two effects on homosexuality in men.
My Older Brothers Made Me Gay
Historically, there have been several reasons offered for the Fraternal Birth Order effect in men, and these theories generally fall along the nature/nurture divide. For the “Made Gay” side, some has taken this as a sign that perhaps the younger boys in a family were treated differently for being the “baby” of the family. But this doesn’t explain why older brothers and not older sisters are associated with homosexuality in men. Another more nefarious theory holds that perhaps these gay younger brothers suffered from sexual abuse at the hands of their older brothers. This wild and unsupported speculation appeared as recently as last month in the Journal of Biosocial Science (the same journal that published Paul Cameron last May).
The “Born Gay” interpretation of the Fraternal Birth Order effects speculates that there may be some sort of immunization to male-specific antigens in the mother when she’s pregnant. According to this theory, when Mom is pregnant for the first boy, she’s exposed to male antigens that her body begins to develop an immunity against. When she’s pregnant for the second boy, the process is repeated and strengthened. At some point, whether it’s during that second boy’s gestation or a later one, her body’s immune system interferes with the sexual differentiation in that fetus’ developing brain. This results in that boy’s sexual and romantic attraction to other men later in life.
My Left Hand Made Me Gay
It’s also been observed that gay men and women are more likely to be left-handed than the general population. (Remember, the Older Brother effect applies only to gay men.) Again, the speculated reasons for this are varied. Some have attributed left-handedness to some sort of developmental instability that, in some cases, may also give rise to homosexuality. Others speculate that prenatal hormonal levels may result in left-handedness, homosexuality, or both.
It’s important to keep in mind that no single theory can explain the development of homosexuality for everyone who is gay. It’s much more likely that there are multiple reasons why someone is gay, and that those reasons are different from one man or woman to the next. In my case, for example, I am the oldest brother out four boys and no girls in my family. I am the only one who is gay, so the Older Brother theories obviously don’t apply to me. But I am profoundly left-handed — my right hand is just there for decoration and balance. It comes in handy (excuse the pun) when I tie my shoes, but that’s about it.
An Interaction Between Fraternal Birth Order and Handedness?
A forthcoming article by Ray Blanchard and Richard Lippa in the Archives of Sexual Behavior examines both of these phenomena. They looked at 2,486 participants from five previous studies, consisting of gay and straight men and women. (The last two samples were volunteers at southern California gay pride events.) After examining the number of older brothers and sisters and the handedness of the volunteers, Drs. Blanchard and Lippa noticed there were two completely independent trends among gay men:
- Right-handed gay men were much more likely to have more older brothers and fewer older sisters than the general population.
- Left-handed gay men were the opposite. They were much more likely to have fewer older brothers and more older sisters than the general population. Gay lefties were also more likely to have older siblings regardless of gender than anyone else, included gay men who are right handed.
There was another trend that Drs. Blanchard and Lippa noticed but couldn’t explain. While right-handed lesbians didn’t stand out much from the general population, left-handed lesbians were much more likely to have more older brothers and fewer older sisters, and they were much more likely to be lower in the birth order than the population overall. This was a surprise. Most other studies that looked at lesbians overall without regard to handedness generally found no correlation to Older Sibling Sex Ratio. But somehow, these left-handed lesbians share older sibling sex ratios that mimic right-handed gay men. Drs. Blanchard and Lippa noted that this is new information that deserves further study.
I found this study interesting, but it certainly opens up more questions than answers. As a first-born gay southpaw, I’m still a statistical anomaly. And there were some other statistical quirks that showed up in this study that the authors couldn’t explain. The biggest one in my mind was this: Why were the straight men more likely to have older brothers in this sample than expected? Their numbers practically matched those of the right-handed gay men.
To me, this is probably the biggest red flag in this particular study, which is why more studies need to be done to confirm these results. But this study confirms another one that was published in the journal Hormones and Behavior. Using a different sample of 3,146 individuals, Ray Blanchard and another team of researchers were able to demonstrate a similar interaction between older brothers and left-handedness in gay men. They observed the that Fraternal Birth Order effect applied only among right-handed gay men, and that gay men with fewer or no older brothers (like me) were more likely to be left-handed than straight men. Blanchard & Lippa note that a third manuscript is being prepared for publication that examines handedness and birth order in the Kinsey sample, and it will confirm this same interaction.
The Bigger Picture — “What Causes Homosexuality?”
The truth is we will never arrive at a single comprehensive theory to explain gayness in everyone. Many anti-gay activists (and pro-gay activists) argue for their favorite theories and against their opponents’ theories based on the assumption that a single theory can apply to all gay people. Research like this one demonstrates the fallacy of that assumption.
Twin studies suggest that for some people their sexuality is genetic or congenital. But since there are examples where one identical twin is gay and another is straight, then this can’t be true for all gay twins. Other studies have tried to prove that parental factors (either a smothering mother or a distant father, depending on the theorist) produce gay offspring. But the fact that there are gay men and women who do not report a smothering mother/distant father is evidence that this can’t explain homosexuality for everyone either. The real answer lies in the individual.
If we are ever able to tease out all of the possible factors that influence sexuality, we will probably learn that there are many different “types” of homosexuality. For some, it may be genetic. For others, maybe their later birth order after a string of brothers. For others still, it may be the same thing that made them left-handed. For others, their left-handedness may be a red herring and the real cause was their distant father. And for others, maybe their absent father had nothing to do with it; prenatal hormones made it inevitable. And for most — maybe all — it is more likely to be the unique combination of any and all of these factors (and others that we haven’t discovered yet) which forms the basis for who we are.
Correction: Commenter “Lij” corrects me on my statement about identical twins. My response is here.