# Identical twins, one gay, one straight

**URL:** <https://boards.straightdope.com/t/identical-twins-one-gay-one-straight/162211>\
**Category:** Factual Questions\
**Created:** [March 18, 2003, 5:20am UTC](https://boards.straightdope.com/t/identical-twins-one-gay-one-straight/162211 "2003-03-18T05:20:45Z")\
**Posts on this page:** 8\
**Page:** 1

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**Author:** ![zgnak](https://avatars.discourse-cdn.com/v4/letter/z/eb9ed0/32.png) [@zgnak](https://boards.straightdope.com/u/zgnak)\
**Post date:** [March 18, 2003, 5:20am UTC](https://boards.straightdope.com/t/identical-twins-one-gay-one-straight/162211/1 "2003-03-18T05:20:45Z")

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Given that sexual orientation is defined at birth, how is it that one identical twin can be straight, the other gay?

Thanks.

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**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\
**Post date:** [March 18, 2003, 5:24am UTC](https://boards.straightdope.com/t/identical-twins-one-gay-one-straight/162211/2 "2003-03-18T05:24:53Z")

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No one has demonstrated that sexual orientation is defined at birth. Twin studies have shown, I believe, that if you have an identical twin who is gay you only have a 50% chance of being gay yourself. All the evidence points to a complex suit of factors (genes, hormones in the uterus, and others that I can’t recall off hand).

I don’t think anyone has yet found a gene (or set of genes) that will predict with 100% certainty ANY specific behavior the individual will exhibit if he/she has that gene (or set of genes).

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**Author:** ![Urban\_Ranger](https://avatars.discourse-cdn.com/v4/letter/u/e9c0ed/32.png) [@Urban\_Ranger](https://boards.straightdope.com/u/Urban_Ranger)\
**Post date:** [March 18, 2003, 6:58am UTC](https://boards.straightdope.com/t/identical-twins-one-gay-one-straight/162211/3 "2003-03-18T06:58:00Z")

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> [@](#):
>
> \*Originally posted by zgnak \*  
> \*\*Given that sexual orientation is defined at birth, how is it that one identical twin can be straight, the other gay?
> 
> Thanks. \*\*

That will be interesting. Do you have any actual cases?

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**Author:** ![Walloon](https://avatars.discourse-cdn.com/v4/letter/w/fbc32d/32.png) [@Walloon](https://boards.straightdope.com/u/Walloon)\
**Post date:** [March 18, 2003, 7:10am UTC](https://boards.straightdope.com/t/identical-twins-one-gay-one-straight/162211/4 "2003-03-18T07:10:40Z")

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ABC News: [Where Did the Gay Gene Go?](http://abcnews.go.com/sections/living/DailyNews/gaygene990422.html)

World Policy Institute: [Twin Studies and Homosexuality](http://www.worldpolicy.org/globalrights/sexorient/twins.html)

ASU Research: [Supporting the Biological Link](http://researchmag.asu.edu/stories/supporting.html)

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**Author:** ![Dunderman](https://avatars.discourse-cdn.com/v4/letter/d/ecb155/32.png) [@Dunderman](https://boards.straightdope.com/u/Dunderman)\
**Post date:** [March 18, 2003, 9:25am UTC](https://boards.straightdope.com/t/identical-twins-one-gay-one-straight/162211/5 "2003-03-18T09:25:09Z")

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> [@](#):
>
> \*Originally posted by zgnak \*  
> **Given that sexual orientation is defined at birth**

At best unproved, at worst unprovable.

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**Author:** ![zgnak](https://avatars.discourse-cdn.com/v4/letter/z/eb9ed0/32.png) [@zgnak](https://boards.straightdope.com/u/zgnak)\
**Post date:** [March 18, 2003, 11:42am UTC](https://boards.straightdope.com/t/identical-twins-one-gay-one-straight/162211/6 "2003-03-18T11:42:15Z")

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Dear Urban Ranger,

Yes, I know of two gentlemen, identical twins, one is gay, the other straight. There is no ambiguity about their stated orientation.

Thanks for asking.

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**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\
**Post date:** [March 18, 2003, 11:58am UTC](https://boards.straightdope.com/t/identical-twins-one-gay-one-straight/162211/7 "2003-03-18T11:58:01Z")

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That’s hardly an impressive statistic.

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**Author:** ![zgnak](https://avatars.discourse-cdn.com/v4/letter/z/eb9ed0/32.png) [@zgnak](https://boards.straightdope.com/u/zgnak)\
**Post date:** [March 18, 2003, 12:02pm UTC](https://boards.straightdope.com/t/identical-twins-one-gay-one-straight/162211/8 "2003-03-18T12:02:26Z")

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Dear Walloon,

Thank you so much for posting the articles or sexual orientation and identical twins. It helped clear up my confusion even though studies and expert opinions are not definitive.

zgnak