Fraternal birth-order and sexual orientation (prenatal effect?)

[Martin]

http://www.pnas.org/cgi/reprint/0511152103v1

 

http://www.pnas.org/cgi/reprint/0511152103v1.pdf

 

Biological versus nonbiological older brothers and men’s sexual orientation

Anthony F. Bogaert

 

Departments of Community Health Sciences and Psychology, Brock University, St. Catharines, ON, Canada

 

The most consistent biodemographic correlate of sexual orientation in men is the number of older brothers (fraternal birth order). The mechanism underlying this effect remains unknown. In this article, I provide a direct test pitting prenatal against postnatal (e.g., social/rearing) mechanisms. Four samples of homosexual and heterosexual men (total n=944), including one sample of men raised in nonbiological and blended families (e.g., raised with half- or step-siblings or as adoptees) were studied. Only biological older brothers, and not any other sibling characteristic, including nonbiological older brothers, predicted men’s sexual orientation, regardless of the amount of time reared with these siblings. These results strongly suggest a prenatal origin to the fraternal birth-order effect.

 

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here is the webpage with the abstract and some other links

http://www.pnas.org/cgi/content/abstract/0511152103v1

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here is a blurb from the publisher (National Academy of Sciences)

http://www.pnas.org/misc/highlights.shtml#Fraternal

 

Fraternal birth-order effect and sexual orientation

 

"Whether the roots of homosexuality are social or biological is hotly debated in psychology. Anthony Bogaert suggests the latter, showing that the number of biological older brothers a younger male sibling has significantly impacts his sexual orientation. In previous studies, Bogaert and colleagues observed that, on average, a higher number of older brothers correlated with higher likelihood that the male individual was homosexual, a phenomenon called the fraternal birth-order effect. In the current study, Bogaert tested whether this effect was due to psychosocial conditioning, such as living with older male siblings, or a biological mechanism. Bogaert studied nearly 1,000 heterosexual and homosexual men in Canada who had either biological or nonbiological (adopted or step) brothers, and how much time was spent with each sibling. Bogaert hypothesized that if psychosocial factors underlie the fraternal birth-order effect, then the amount of time a male individual is raised with older brothers should be predictive of sexual preference. However, Bogaert found that only the number of biological older brothers, regardless of whether they were raised together, predicted sexual preference. Other predictors, such as time reared with older brothers or the number of nonbiological older brothers, did not correlate with the younger male sibling's sexual orientation. The finding supports the idea that sexual orientation has biological origins. — B.T."

 

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Scientific American also picked up on this:

http://www.sciam.com/article.cfm?chanID=sa003&articleID=0005A6D3-7ADC-14A0-B6C483414B7F4945&ref=rss

[Martin]

the suggested mechanism is an IMMUNE RESPONSE to some male-specific proteins, which the mother develops during earlier pregnancies with male children.

 

the mother's immune system (it is conjectured) can develop ANTIBODIES to one or more male-specific proteins----which her immune system recognizes as foreign.

 

the presence of these "anti-male" antibodies in the mother, when she is pregnant again, could have a prenatal effect on her later son(s).

 

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the present research was testing to see if the fraternal birth-order effect could have NON-BIOLOGICAL explanations.

 

it appears to rule out non-bio causes. gayness does not correlate with having older brothers if they were by a different mother.

gayness correlates with having older brothers even if one did not grow up in the same household with them. and so on.

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this is not something I have read much about,

just learned about it.

I can't answer further questions, myself. But maybe someone else knows more.

I think it is very interesting because it points to a biological effect which however is not GENETIC. It is more in the department of OB/GYN medicine and the field of IMMUNOLOGY.

 

It is also may possibly raise some ethical issues, since antibody levels can in some cases be tested-for and perhaps even controlled-----it raises the possibility of elective intervention. However that is way far in future, since this present research is just beginning the project of finding out how the fraternal birth-order effect works.

[Mokele]

I'm not sure they did the statistics right. On one hand, they used a scale of sexual orientation, rendering it a continuous variable, which means that linear regression was appropriate. However, at the end of the methods section, it's noted that the vast bulk of the respondants characterized themselves as at one of the extremes of the scale. I'm no statistician, but I'd think this would adversely affect the results, since you've essentially got two lines.

 

Personally, I'd be a lot more convinced if they'd at least said "and then we divided the subjects up into gay, straight and bi categories and performed logistic regressions, and here are those results", since then I'd know that they aren't just picking the analysis method that gives the best results.

 

I do think they have a good point, but given that the paper is almost entirely statistical, I would at least expect a bit more complexity than "we did an assload of linear regressions".

 

Mokele

[Martin]

...I do think they have a good point' date=' but given that the paper is almost entirely statistical, I would at least expect a bit more complexity than "we did an assload of linear regressions".

 

Mokele[/quote']

 

Well put. I appreciate your point.

 

As you can imagine, I have no interest in arguing about the statistical methods.

 

My impression is that the Fraternal Birth-Order Effect is already well established. I.e. there is already a recognized solid correlation between the number of older brothers a male has and his likelihood of being gay.

 

Is that your impression also, or do we need to doubt that as well?

 

To me the FBO effect seems already pretty interesting

 

I would have assumed that it was a social or psychological thing associated with growing up with older brothers. But apparently it DOESNT CORRELATE with that! It correlates with your mother having previously BORN male children whether or not you spent time in their company. So I am already surprised by the results in this paper----that they didnt find a simple correlation with how many brothers you grew up in the house with.

 

Too bad if the statistical methods weren't so good. Hope someone reanalyzes the data in more appropriate ways and compares conclusions.

[Mokele]

My impression is that the Fraternal Birth-Order Effect is already well established. I.e. there is already a recognized solid correlation between the number of older brothers a male has and his likelihood of being gay.

Is that your impression also, or do we need to doubt that as well?

 

Well, it's my impression, yes, but I've not actually read the papers themselves.

 

As you can imagine, I have no interest in arguing about the statistical methods.

 

Of course, but it should be pointed out that without addressing this statistical issue, we can't know if the results are actually significant or not. What if the results are not significant when analyzed using logistic regression? That calls the who study into question. Basically, all of the methods are statistical in this paper, so this issue does mean that you have to be a bit more skeptical.

 

Mokele

[ecoli]

like many things in science, without an established mechanism, you merely have correlation that may very well be meaningless.

[Mokele]

However, such correlations are often the first clues as to the mechanisms, and give us an idea of where to look.

 

Mokele

[swansont]

However' date=' such correlations are often the first clues as to the mechanisms, and give us an idea of where to look.

 

Mokele[/quote']

 

 

And this points away from environment as a cause, and toward biology.

[Sisyphus]

And this points away from environment as a cause, and toward biology.

 

Or maybe not! Birth order has a lot of big statistical correlations in psychology, and as far as I know there's no difference between biological siblings or adopted siblings.

[swansont]

Or maybe not! Birth order has a lot of big statistical correlations in psychology, and as far as I know there's no difference between biological siblings or adopted siblings.

 

Umm, did you read the first post? This study addresses precisely that issue, and saw a difference.

[Sisyphus]

Umm, did you read the first post? This study addresses precisely that issue, and saw a difference.

 

No I didn't! Touche....

[Severian]

That is interesting, particularly for me since I have an older brother who is not genetically related (he was adopted).

 

Presumably the next thing to test would be to see if homosexual men's mothers had a higher number of miscariages than normal (before their birth). In other words, do the babies have to be brought to term to have an effect?

[Martin]

That is interesting' date=' particularly for me since I have an older brother who is not genetically related (he was adopted).

 

Presumably the next thing to test would be to see if homosexual men's mothers had a higher number of miscariages than normal (before their birth). In other words, do the babies have to be brought to term to have an effect?[/quote']

 

that is a smart question and I think would justify an email to the author of the paper

 

he has conjectured there might be an immunological effect and I imagine that if one knew the gender of the miscarried infants that would definitely be a statistic to look at----being pregnant with a male child (whether or not carried to term) could trigger production of antibodies to some male-specific proteins.

[silkworm]

This is an interesting study. I've been hearing about this study, a study that found that the mothers of homosexuals generally have sisters who have a lot of children as well, and an intersting study that compared the brains between the brains of gay and straight men who all died of AIDS. I also heard many stories about homosexual behavior amongst many different species.

 

Very intersting stuff, but unfortunaly I'm afraid that homosexuality having a biological cause will never be accepted by those with agendas other than understanding.

 

They've been all over the podcasts recently.

[Martin]

...homosexuality having a biological cause will never be accepted by those with agendas other than understanding.

 

They've been all over the podcasts recently.

 

ai ai

think of an agenda as an evolving organism----those agendas which evolve practices favoring a high birth-rate will tend to predominate and fill the niches.

 

so they are up in arms in the podcasts:-) what a great word that is!

 

by the way, I'm not, but someone I love is, so it is clear to me which side I'm on. I dont come to it from ideology but from experiential bedrock. the older I get the more I want to dispense with ideology and hold only to what life has taught

 

damn them and all their podcasts

[ecoli]

Very intersting stuff, but unfortunaly I'm afraid that homosexuality having a biological cause will never be accepted by those with agendas other than understanding.

 

It's interesting because there are homosexuals who have their reasons for rejecting a biological cause and there are also 'anti-homosexuals' who have their reasons for rejecting a biological cause.

[silkworm]

ai ai

think of an agenda as an evolving organism----those agendas which evolve practices favoring a high birth-rate will tend to predominate and fill the niches.

 

so they are up in arms in the podcasts:-) what a great word that is!

 

by the way' date=' I'm not, but someone I love is, so it is clear to me which side I'm on. I dont come to it from ideology but from experiential bedrock. the older I get the more I want to dispense with ideology and hold only to what life has taught

 

damn them and all their podcasts[/quote']

 

Oh no.

 

I didn't mean to imply that the podcasts were degrading the studies into meaningless quibble. I listen to a lot of science podcasts, and there has been a lot of work in studying the biological cause of homosexuality, that's all I meant.

 

There appears to be many factors involved in genetic predisposition towards homosexuality, but there is no disputing that increasing predisposition is even an indirect result of being the offspring of an successful organism makes immense amounts of sense for a biological cause. The other studies seem to be more of an explaination of biological indicators of homosexuality and not really a cause. The conclusion has come that the factors are so many that there is no "gay gene," (which is not to say it doesn't have a biological cause) and that it would be exceedingly complex to "cure" someone of homosexuality.

 

Download iTunes Martin (it's what I use, makes things easy to find and keeps things organized, user friendly too). Subscribe to some free science podcasts, you will love love love them.

[silkworm]

It's interesting because there are homosexuals who have their reasons for rejecting a biological cause and there are also 'anti-homosexuals' who have their reasons for rejecting a biological cause.

 

I could see why homosexuals would want to reject biological cause, because fear that it may imply inferiority or anomoly. But it appears to me that that is not the case at all. There are simply factors that lead towards its tendency, factors that even show the evolutionary success of one's lineage, and biological indicators that are a result.

[Mokele]

Presumably the next thing to test would be to see if homosexual men's mothers had a higher number of miscariages than normal (before their birth). In other words, do the babies have to be brought to term to have an effect?

 

Actually, the authors mention examining the effects of prior miscarriages and abortions at the end of the paper.

 

Mokele

[Martin]

Actually' date=' the authors mention examining the effects of prior miscarriages and abortions at the end of the paper.

 

Mokele[/quote']

 

Great! I missed that, or it slipped from memory. thx for pointing it out.

[abciximab]

Hmm, *if* that is proved to be a cause-effect thing rather than a pure association, it could bring up a very interesting purpose for homosexuality.

 

I've always wondered if homosexuality is intended to be a form of population control, and whether our population's recent increase in acceptance of homosexuality relates indirectly to the fact that we are quickly becoming overpopulated and realize that we don't need everyone having kids anymore.

 

Maybe the hormonal feedback that causes later born sons to be homosexual is an intrinsic population control method; attenuating the number of sexually viable men that a mother produces.

 

If they talk about this in the article sorry for being redundant, I didn't read it because I'm in a bit of a hurry...

 

Do the authors mention whether having girls in between resets, reduces, or doesn't affect this effect?