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.

* * *

Are you a gay male?  What is your birth order?  What does your sibling lineup look like?

Are you raising a gay male or gender nonconforming son?  What is their birth order?  What does their sibling lineup look like?

C.J. is gender nonconforming, the second of two sons.


About raisingmyrainbow is a blog about the adventures in raising a fabulous, gender creative son.
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86 Responses to The Fraternal Birth Order Effect

  1. Adam P says:

    Curious does this apply if there is a total of 3 boys.. Not 4, and has 3 older brothers.. Just 3… Is it still the youngest one then that is gay? Just curious

  2. Trish says:

    I have a bunch of gay friends and they are 90% always the middle child…it is weird…but my older son is gay out of two boys bur I miscarried at 16 weeks four years before I had my son who is gay…so technically he would have been the middle child. So who knows?

  3. Joe says:

    I have 2 brothers, and 1 sister, I am the youngest, and I am gay, my older sister (15) is straight, my older brother (17) Is straight, and my oldest brother (18) is gay. So in reality, I’m the third son, so it makes sense!

  4. Ali says:

    I am the oldest of four boys, and I am pretty sure im the only gay one. I have experimented with females in the past so some may label me bisexual, however I consider myself gay. Though i do not subscribe to this theory, interestingly, I should be the second child in line since my parents opted for abortion for my unborn sibling. That makes the theory plausible, but in light of neither of my younger siblings being homosexual or bisexual identifying, I disagree with the theory.

  5. stephanie says:

    My first born is a 5year old gender creative son (who we refer to as daughter now as was requested) our second child is a girl and only 1 year old 🙂

  6. Amadeo says:

    I’m from a family of seven boys and one girl. The only sister is seventh in line followed by the baby boy. I’m just before her as the sixth son. I identify as homosexual and out family fits the findings of the study perfectly. Even though my baby brother, and also only brother younger than myself, is cisgender heterosexual, he fits into the outlier group of left handers. He’s the only lefty in the family as well.

  7. jefXfree says:

    I am the oldest son and i’m gay. My younger brother is happily married. I’ve heard this theory before, but my birth order always made me at least partially discount it…

  8. Jess says:

    There are two gay men in my family: one conforms to this rule and one contradicts it. My father has two brothers (one living, one sadly deceased) and a sister. The oldest, his deceased brother, was gay. The other gay man in my family is the second in a family of two boys. Interesting theory! Funny how it only works with boys though. Also, I’m confused about labeling C.J. as “homosexual.” If he identifies as a female and is attracted to men, then wouldn’t that make him a queer heterosexual? Labels are lame anyway.

    Congrats on your wonderful family and keep being the best parent ever!!!!!!!!!

    • TransKid says:

      Youngest of six, four older brothers. But I’m a trans boy, so I don’t know if that affects the data. Plus three of my brothers are from another mother. But I am gay. Or bi.

  9. perfb says:

    I have two gay uncles, one was an only child from a young 15 year old mother, other was a younger brother, born 9 years after the older brother from a mother in her late 30s. Both are into brutal sadomasochism too, as evidenced by their porn collection.

  10. hap2130 says:

    I’m the oldest… Mom had 4 kids, my full bro is straight, and my sister and baby bro are straight… so far! 🙂
    Like Tigger – I’m the only one!

  11. Christophe says:

    I’m third of four: my elder sister, elder brother and younger brother are all straight.

    I just discovered your blog: it’s really nice! I read all of it in a few days. I’m glad you’ve chosen to continue with it.

  12. Elizabeth says:

    I’m the eldest, and lesbian. My only brother is also gay. That’s it, just us. Our parents bat 1000.

    I’m interested in this concept though, because my mom has 5 brothers. The fourth (predictably, since he had a 99% chance) is gay, but the 5th is not. Do womb reset?

    This seems like an instance of statistics being manipulated to prove themselves.

  13. Jeremy says:

    I also found your blog through the “Where Do Gaybies Come From?” site, and can’t stop reading now. I was a little kid like this, who life kind of knocked the purple out of as I grew up. I’m grateful to be an adult know who makes his own decisions about how sparkly to be each day, but as a teen there were times it was painful to hide my purpleness and be a conformer. Thanks for documenting how you’re raising your kid – hopefully with your support he won’t feel the need to suppress himself for years on end.

    I’m the oldest of seven, with two of them being younger brothers. They seem to just have gotten straighter and straighter after me. However, my nephew is also the oldest, and reminds me of me when I was 4, while again his younger brother is 100% boy. Maybe my family does it backwards.

  14. Phillip says:

    I am a gay male, and I am the first-born. My younger brother by 3 years is straight. Apparently the fraternal birth order effect isn’t the only thing going on. I just found your blog today, by the way, from Where Do Gaybies Come From? ( and I am enthralled. You both seem like such amazing parents, and all kids like C.J. should be so lucky. I am another completely supportive reader.

  15. My son is the the only male but the second live born. Before my two live born I had 8(!) miscarriages.

    My son is pinkish.

  16. Bertie says:

    I’m number one of three boys and I’m the gay. My younger brothers are both startlingly red-blooded males and out-macho me just by breathing. In truth they out-macho an entire rugby team.

    Interestingly my mum is the youngest of 5 girls and one boy (5th born and gay). All of my 15 first cousins are female.

    There you have it, everything in my family line is hinged on my brothers.

  17. JMW says:

    My twin and I are both gay, and we are the only boys out of 5 children. Two older sisters, and a younger sister.

  18. discover411 says:

    I’m gay, but I’m the eldest one in my family (I guess the Fraternal Birth Order Effect doesn’t apply to me. Maybe genetics?)

  19. Cameron says:

    I’m gay and I’m the younger of two brothers.

  20. AJ says:

    I’m the oldest of three children, I’m male, and I’m gay. I’m not very overtly gay, though, and I could “pass” as straight in nearly all situations.

    My younger brother (the middle child), in contrast, is straight, but has as many gay tendencies as I do, if not more. I play sports. He takes ballet. I’m a writer. He’s a graphic designer. We’re both heavily into musical theater.

    My sister (youngest) is straight, and also into many of the same things I am. Some sports, musical theater, etc.

    I personally believe it’s neither nature nor nurture, but a combination of both. I believe I was genetically inclined to be gay, but the fact that I was raised in a very liberal society (eastern Mass.) made me more comfortable with the idea from an early-ish age. If I’d been raised in an antithetical society, say, Idaho, I probably would have buried my inclinations and led a “happy” but unfulfilled life as a straight man.

  21. Eric says:

    Also, in regards to the sexuality of children thing, I remember being sexually attracted to boys in kindergarten. I remember having my first crush on a boy from Goosebumps T.V. show in second grade.

  22. Eric says:

    I have two brothers, and I am the middle child. The eldest is straight and right-handed. I am gay and also also right-handed. My little brother is gay as well, but he is left-handed. Can you imagine how lucky my mom is to have two gay children!

  23. AG says:

    I am a straight woman and my twin brother is a gay man. We are the only children but my mother had a stillborn boy about a year before we were born. I agree with some of the other posters that this seems like an arbitrary thing. However, I certainly agree with you about hoping that when science/technology figures out what causes homosexuality that no one messes with it. There shouldn’t be any negativity attached to having a gay child and treating sexual preference like a disease or genetic/birth defect, and “correcting” it before birth or conception would be unconscionable.

  24. Paul says:

    I am the third born child second son who was the “baby” until the age of five when two more boys came along one right after the next. Maybe my mother’s womb “re-set” after a five year break? All four of my siblings identify as hetero. I was a pink boy and felt like the cuckoo in the nest for my entire youth. In fact, I learned quite young (around the age of five) that it was safer to try and hide who I was from everybody, family & friends not just the outside world. I am glad that C.J. and many other pinkboys do not have to suffer the stress that I and all of my generation had to endure. Who knows how many of us cracked under the strain and ended their lives. I don’t look back at childhood as a magical time but as a horror movie that I finally escaped as an adult. Many years of what I know I now realize was PTSD have passed and I now think of my self as “integrated’, not 100% male but not female either, but all ME.
    I didn’t know him very well but I suspect my mother’s only sibling was gay. My sister’s second son is gay and was a pink-ish boy too.

  25. Day Gyselaar says:

    I’m the only son of my mother and I’m gay. However, I was a fertility drug baby, so I don’t know if that has anything to do with it?

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