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Mar 1 17 9:01 AM

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Harvard University has a pretty good overview over recent research on transgender people here http://sitn.hms.harvard.edu/flash/2016/gender-lines-science-transgender-identity/ which includes this figure:


 image
I think it captures at least some of the complexity of sexuality and gender, and especially the fact that even though you will find the majority of people in some big clusters, there are -- in fact -- people all over the maps.

(I wish, though, they had used the term non-binary for genderqueer people, instead of "two-spirt", as that is a term that primarily refers to some Native American traditions.)

This article argues that transgender conditions most likely have a genetic component, and the author refers to twin studies to strengthen this argument.
First and foremost, is gender identity genetic? It seems the answer is yes – though, as with most traits involving identity, there is some environmental influence. One classic way for scientists to test whether a trait (which can be any characteristic from red hair to cancer susceptibility to love of horror movies) is influenced by genetics is twin studies. Identical twins have the exact same genetic background, and are usually raised in the same environment. Fraternal (nonidentical) twins, however, share only half their genes, but tend to also be raised in the same environment. Thus, if identical twins tend to share a trait more than fraternal twins, that trait is probably influenced by genetics. Several studies have shown that identical twins are more often both transgender than fraternal twins, indicating that there is indeed a genetic influence for this identity.


Are there any of you who knows more about twin studies and how they can be used to "prove" inherited traits?  I understand that this is a matter of statistics, in the sense that if there are more transgender twins that there should be if everything was left to chance, there is most likely a genetic component. Still, there are a lot of identical twins where only one person come out as trans.