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Scanning sexuality

A study published recently in PNAS reported that people's sexual orientation is reflected in their brain structure. MRI scanning revealed that the two hemispheres of homosexual men's brains are equal in volume, like those of heterosexual women. Similarly, the right hemisphere of homosexual women is slightly larger than the left hemisphere, as is the case for heterosexual men. In addition, positron emission tomography showed that this structure/sexual-orientation relationship also applies to amygdaloidal connectivity.

According to Qazi Rahman of the University of London, this relationship “...makes sense given that gay men have a sexual preference which is like that of women ... and vice versa for lesbian women.” ( BBC News , 16 June 2008.)

The results reignite the debate over whether people's sexual orientation is already fixed when they are born. For Rahman, “...there is no argument anymore — if you are gay, you are born gay.” (BBC News, 16 June 2008.) Ivanka Savic, one of the study's authors, agrees that the data are “...difficult to explain by a specific learned behaviour....” ( National Geographic News , 16 June 2008.) However, Sandra Witelson at McMaster University says that this “...doesn't mean that environment is a hundred percent irrelevant.” (National Geographic News, 16 June 2008.) Indeed, the extent to which the structural features arise from an individual's genes, from the conditions in the womb and from the later environment also remains an open issue.

Another question is whether the relationship observed in this study extends to other brain areas. As Eric Vilain of the University of California at Los Angeles puts it: “In gay men ... is [the feminization] limited to particular areas, or is the entire brain female-like?” ( LA Times , 17 June 2008.)

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Nicholson, C. Scanning sexuality. Nat Rev Neurosci 9, 582 (2008). https://doi.org/10.1038/nrn2454

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