The Fraternal Birth Order Effect

The Fraternal Birth Order Effect. It sounds super serious. Like a group out of The Da Vinci Code, a fraternity at Harvard or a secret club of the uber-rich and houtie toutie. I feel like there are secret handshakes involved, aged scotch in snifters, dark wood paneling and signet rings. Men in ascots for sure.

A reader tipped me off to the Fraternal Birth Order Effect some time ago, but the name seemed daunting and, frankly, I’ve been too tired for research and the new season of Project Runway is in full swing.

But, on Friday night, while my husband was at work, in the quietness of the house after the boys’ bedtime, I could hear Google calling. I stayed awake until midnight (that’s 3 a.m. in Mom Time) reading everything that I could about the Fraternal Birth Order Effect.

The Fraternal Birth Order Effect is proven to mean that for each older brother that a physical male has his chances of being homosexual increase by approximately 33 percent. According to several studies, the Fraternal Birth Order Effect is the strongest known predictor of sexual orientation. The same is not true for females. Have lots of older sisters? It doesn’t increase your chances of being a lesbian. Sorry, this predictor of sexual orientation is for boys only.

The Fraternal Birth Order Effect holds true for boys born from the same mother but not raised together. It does not hold true for boys adopted into the same family. Therefore, it has an “in-utero environmental causation.” Which is a big fancy way to say it happens during pregnancy.

After my Google fit, I couldn’t stop thinking about all of the boys I know who have multiple older brothers. I was counting little gay brothers to go to sleep. I thought of those shirts they sell that say “I’m the Big Brother” and “I’m the Little Brother.” The last-born son should have a shirt that reads “I Have the Highest Chance of Being the Gay Brother.”

I couldn’t stop thinking about families with lots of boys. The Beckhams. The Jonas Brothers. The Kennedys. The Marx Brothers. The Duggars. Oh no, not one of the 10 Duggar boys…

It is hypothesized (look at me using big words!) that the Fraternal Birth Order Effect has “something to do with changes induced in the mother’s body when gestating a boy that affects subsequent sons. ” (source: Wikipedia)

“The theory suggests that mothers during childbirth may develop antibodies to proteins made by their firstborn son’s Y chromosome, and subsequent pregnancies may stir up those antibodies in an immune reaction that affects the development of a male fetus.” (source: San Francisco Chronicle)

In the next decade or so, C.J. may need a shirt that reads “I Was the Last Son in My Mom’s Uterus and All I Got Was This Stupid Sexuality.” C.J.’s Brother may very well have stolen the heterosexuality right out of my womb.

Maybe heterosexuality proved no match for the kick ass antibodies my body created in response to carrying my first son. My antibodies should have capes and masks and patent leather, knee-high stiletto boots.

I was proud of my antibodies for a minute, thinking that they were superheroes. Then, I thought, what if science learns to alter those antibodies so they decrease the likelihood of the Fraternal Birth Order Effect? Could women and doctors start messing with hormone injections during pregnancy to prevent homosexuality?

Maybe, one day, when I have the courage and energy, I’ll try giving that a Google.

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  • Z

    Well, I’m sure LGBT that use surrogate mothers or figure out a way to craft their own egg/sperm will want to use the reverse hormone treatment to ensure that the gay race survives.

  • Scott

    This “antibodies” theory sounds like crap. I resent these theories that imply that things didn’t go right and a gay child was born, that heteros are better. I am not a birth defect. I’ll bet there are 2 genes somewhere that govern sexuality and 2 recessive ones got together in my case.

    No matter what technique was used to create me I’m sure I’m exactly the way the universe intended me to be. I’m perfect the way I am.

  • ibarra

    z, as far as i know there is no “gay race.” there is only the human race–that’s why we’re all fighting for equality.

  • James UK

    I am the eldest of 3 boys. The younger 2 are straight, married with a kid each.

    I am the gay one – the very gay one.

    I think that we are born gay. Whether it is genetic or due to in utero hormone levels or a combination, doesn’t matter to me. There is nothing wrong or abnormal about being gay. It’s nothing that I’ve ever felt the need to apologise for or explain away. I am as good as anyone else, gay, straight or anywhere else in between.

  • Patricia

    @ibarra: Yes Human race with the need, and right for equality

  • Patricia

    @James UK: We are born how we are supposed to be. I am a Transsexual I feel I was born, as I was supposed top be, for something yet to be revealed to me. Perhaps to educate people about normal People All of us included

  • Arek

    Scott: Ignoring or resenting scientific data because it doesn’t jive with your beliefs is exactly the kind of thinking that the religious right uses against us gays. The fact that you’d prefer it to be a different way doesn’t make it any less true.

    But you said it yourself: who cares what makes us gay?

  • Marriage Equality

    I dated a guy who was one of 4 brothers – all 4 were gay!

    I also have a friend who is one of 9 kids – 6 turned out gay… Irish Catholic Family, eventually the parents told everyone the 3 straight kids were a mistake! lol

  • Mike

    it shouldn’t matter why we’re gay but it does because some goat herders 2,000 years ago wrote some laws to help control their population that somehow got picked up by the Romans and passed down to us as some sort of divine revelation.

    religion ruins everything and until we, the human race, grows up and throws off the shackles of superstition – if they find out what makes us gay, they will try and ‘solve’ it.

  • JKM

    What crap…the vast majority of gay men I know are first born sons and most of them are the first born child. A few of my friends are the last child and fewer yet the last son and even fewer are middle children.

  • QJ201

    Actually the three things that have been found to predict homosexuality in males are: Genes, Hormones (aka the maternal stress theory), and Birth Order.

    If people want to call science “crap” fine. The fact is the more evidence there is supporting that homosexuality is not a choice can only help us in our fight for civil rights.

    And yes I’m the oldest too, but the maternal stress theory explains me (mom was in an accident during her pregnancy with me), lol.

  • Browning

    @James UK:

    I pretty much had in mind to say the exact thing that James UK had already stated. I too, am the oldest of 3 boys and the only gay one. For that matter most of my gay friends are either the oldest male member of their siblings or an only child.

    Even if it is ever proven without a doubt that homosexuality is “caused” by some hormonal imbalance during pregnancy or a simple genetic happenstance I am thrilled that it happened to me. Most of may gay friends and the most loyal, creative and loving people I know and the world is lucky to have them.

  • Andrew

    There’s a big difference between the social phenomenon of being gay and the scientific one. No-one likes to think they are “damaged” but evolutionarily, it doesn’t make sense for children to not want to breed (the group evolution ideas – i.e. gays are good for the tribe, so gay genes survive – have been ruled out. Selfish genes will always win over altruistic ones). It seems most likely that homosexuality is just a bearable consequence of the complexity of human attraction and sexuality, in the same way that difficult births are a bearable consequence of humans standing upright. We CAN breed, if things get desperate, but we probably won’t want to. Still, we won’t lead to the extinction of our species (unless you believe the hard-line religious).

    Evolution doesn’t want or intend us to be anything, though. It doesn’t fail or succeed, since it has no goals. It just changes things, tries to kill everything, and sees what survives, then does it again. It can tell us nothing about how we should live or what we are ‘destined’ for. It just adapts us to be where we are.

  • Jim Hlavac

    OK, so we have represented here in this little survey of Fraternal Birth Order: older sons who are gay, middle boys who are, and youngest sons, too. We have one gay boy out of a passel of a few boys, and we have multiple gay sons in one family. I’m sure by day’s end we’ll have single sons with either older or younger sisters, too, and guys with lots of sisters but no brothers, and only children, too, I’m sure. We will also have twins where both are gay, and twins where one is gay and the other is not, and that be for both identical and fraternal twins. And so from this rather unscientific snapshot of us here, we can safely conclude; birth order has absolutely nothing to do with whom is gay or not.

    Moreover, the idea is predicated on surmising that something was done to us externally to make us gay in a psychological way, rather than physically internal. For if the “younger son is gay” theory is true, then, well, wouldn’t all the youngest sons be gay all the time? Or the oldest, or which ever confounded combination might be found?

    Meanwhile, in the larger picture, there are 106 boys born for every 100 girls. 2 or three girls are the lesbians, and 6 to 8 are the gay guys. Hello gentlemen, God did put us here, for we are that extra 6, I do believe. And look, it even matches our supposed percentage of the population! Wow.

  • Samwise

    This effect only accounts for 1/6th of gay guys out there. There are plenty of gay men with no older brothers, and plenty of straight men with lots of older brothers. Interestingly enough, gay men are more likely to be left-handed – but not if they have older brothers. So apparently, there are a few different ways to make a gay baby, and scientist have just uncovered one.

    I don’t think this means we’re a defect or anything. We’re a means of population control, a way for nature to say, “You’ve got too many boys who’ll make too many new babies for the tribe to take care of. Here, have a boy who won’t make more babies and instead will take care of the ones you already have.” That makes sense to me, anyway.

  • CPT_Doom

    @Andrew – if altruistic genes lose out to selfish ones, why exactly do bees and ants survive? Their entire species are based on altruism. And if homosexuality is a side effect of human sexuality, why are there hundreds of non-human species that include homosexual and bisexual members? Birds, for instance, have long been known to have homo pairings, complete with raising orphaned chicks (it doesn’t just happen in captivity), and they have some of the oldest DNA still in existence.

    I know of now scientific research that has proven or disproven any evolutionary rationale for homosexuality – hell, it is barely mentioned at all in such research, and biologists have only recently (eg., last few decades) begun actually admitting homosexuality has a place in the natural world. It certainly makes sense, in a species that lived as nomadic tribes for quite some time, to have spare adults around to help with food gathering, hunting, raising orphaned children and even just babysitting older children (a woman not on birth control will have a healthy baby every 18 months – 2 years, so there would have been a lot of older kids needing watching running around those tribes).

    As for the science behind homosexuality, it will likely be years before we fully understand the mechanisms that lead to LGBTI people, but I personally would be shocked if they weren’t all related. From what we do know of embryonic and fetal development – a mass of eight cells transforms into a human baby through a complex series of inputs from genes, proteins, hormones, enzymes, etc. – not only are LGBTI people understandable, they are actually predictable. The very existence of Intersex people (the I above) demonstrates that fetal development can result in a pretty non-standard human physicality (e.g., a woman with testicles), so we shouldn’t be surprised to find there are many more people who have “normal” physicality, but brains that are not typically gendered.

    The best explanation of all us humans who deviate from the standard model was an evolutionary geneticist who described us as the “guinea pigs of evolution.” That is, because evolution requires constant mutations and the different characteristics that come from them, those of us who are a bit different are just an example of evolution at work, and you never know what trait will be the next successful one.

  • pierre

    @CPT_Doom: I agree. My last husband was a woman with testicles.

  • phallus

    Does this have anything to do with the fact the The Queen’s English doesn’t contain the letter “z” in its alphabet? Don’t any of these researchers have anything better to waste their money (and the schools..ie taxpayers) on? What ever happened to George Carlin’s dark closet theory? This alone could save these researchers time and money!

  • Andrew

    @ CPT_Doom, Bees and ants are indeed very altruistic, but they work by an entirely different method. Since only the queen is fertile and all the other ants/bees are infertile brothers and sisters, the whole nest/hive could be treated as a single evolutionary player, like the hands, mouth and arms of one person. In a human tribe, everyone’s competing to pass their own genes on. Genes which predisposed you not to have your own children or to care for other people’s in preference to your own would not be passed on, simply because you wouldn’t have any children to pass them on to. Hence, if being gay (not so much bi – you’d still breed yourself) was genetic, the genes would vanish, unless those genes, most of the time, give some kind of breeding advantage and we’re just the occasional fluke.

    I hope I’m not coming across as saying that gay people are lesser because of this. That’s what I meant when I said about the social phenomenon. We just don’t think in evolutionary terms. Many of the qualities we value most can only be explained by these ‘misfirings’ of evolutionarily developed desire: sacrificing your life for a stranger or adopting children for example.

    I don’t know why people want to be intended by evolution anyway. If we’re personifying it, it’s hardly a nice person. As an example, there’s a simple reason why a self-limiting population isn’t a good explanation for the Fraternal Birth Order theory: Nature already has an incredibly effective way to limit a population that grows too large to support itself – the weakest children starve to death.

  • Andrew Macdonell

    Also, we can’t just take a poll of people who comment on here to prove or disprove the Fraternal Birth Order effect. There are so many human psychological tendencies which mess with that kind of data gathering. The studies into it should be scientifically rigorous. If they’re not, then we can say it’s nonsense, but if they are, then it’s reasonable to think there’s something behind it, no matter how many anecdotes would oppose it. As Ben Goldacre brought to my attention (wonderful man) “The plural of anecdote is not data”.

  • hi2u2

    My Oldest Brother was born 9 years before me and the middle brother is 4 years older. So the theory fits in my case. But I don’t view it as a ‘defect’ or anything negative. If it is why I’m gay then so be it. Im openly gay and happy. I wouldn’t change a thing.

  • Bryan

    Hmm, it means the youngest Jonas brother might be gay…not bad.

  • hmm...

    Unfortunately, this is merely a case of poor scientific reporting i.e. journalism.

    1) The study was not intended to provide the ONLY means of explaining male homosexuality. It merely put forward the notion that there is a clear link between birth order and male homosexuality. When I read about it, it was stated to be the only irrefutable sign in pre-determining male homosexuality.

    2) Though of course is it an objective finding, the reporting of it by science would be subjective and may be subconsciously pitted against the heteronormative standards – bare this in mind. Even if it uses the incorrect phrasing making you (as a male homo’) appear an ‘error’ that’s not how you have to read it. It’s a fact which so far many have provided suggestions to explain. Science has a history of biased reporting.

    3) The birth order study actually took into account not only live births but those previously ‘aborted’ (naturally or otherwise) males foetuses, which is how first born male homosexuality could still be explained by the findings.

    4) You are and always will be special.

  • Mike in Asheville

    Mom should stick to letting CJ be CJ.

    Mom wrote: “The Fraternal Birth Order Effect is proven to mean that for each older brother that a physical male has his chances of being homosexual increase by approximately 33 percent.”

    WRONG WRONG WRONG. The FBOE is an OBSERVATION; it is not a fact, it is not a theory, and it most certainly is not PROVEN. It is an observation; and, even by its own researchers, an observation regarding 1 in 7 gay men. OR, hardly worth noting at all.

    Even the Wiki page Mom references offers a decent review of the studies and counter-studies.

    Researchers do research: is there any correlation of homosexuality based on the order of birth? The research shows that is no correlation when it comes to women. The research shows that there MAY be a correlation among men, that there is a higher, slightly higher that is, likelihood that successive boys by birth are gay than their older brother.

    As contraindicated by other studies, there are substantial flaws that have not been into account in the FBOE studies, particularly, the pool of counterbalance among the number of children born: there is no reference available when there is only one boy in the family; there is only 1 reference in families with 2 boy, etc. Since many more than not modern nuclear families have 1 or 2 boys rather than 3+ boys, the research is skewed in that NO families with 1 boy are in the pool sample.


    I believe that understanding the particulars of the human race is important study for improving the human condition, and applaud sincere efforts of analysis of us all. Without scientific research and analysis, we would not have evolutionary biology.

    Unfortunately, too little information misunderstood by too many people is dangerous. Remember, it was just over 500 years ago, IT WAS A FACT THAT THE EARTH WAS FLAT.

  • AgBoiNV

    @Scott: I think ti is interesting that many times soocial structures lead many of us to interpret this type of outcome as inferring a “defect” or that “something went wrong”.

    Ironically, I propose, a very sound argument can be made that this is nature’s way of doing something RIGHT (although the bigots out there, who are incapable of logical thinking on matters of sexual orientation would never accept it). I think of it this way: in many species there is a sort of optimal mix of males and females in the actively-breeding population. It makes sense (even under theories like Intelligent Design….yeah, I said it) that a species like humans, where biological breeding patters would mean a higher ratio of females to males would “figure out” a way to solve this problem……..the more males a mother has had, the less need for all of them to be straight (ie- be in the active breeding populaiton), so naturally a trigger kicks in to readjust the ratio.

    It might sound out there, but I don’t think it’s too far off the beaten path…..and definitely bullwhips these “defect” shenanigans.

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