As many of you know, the human skeleton differs between biological males and females. This is especially visible in the pelvis (hip bones). These differences become greater during puberty and are thought to be largely driven by sex hormones (e.g., estrogen, progesterone, testosterone). There is also some thought that genetics are involved. This study examined whether trans individuals have the skeletons of their sex or their gender. For female-to-male trans men, do their pelvises look like female pelvises (sex) or male pelvises (gender)? If their skeletons do not match their sex, the evidence that transsexuality is biological would be strengthened.

The authors compared various measurements of the pelvises of trans men, cis men, and cis women. All the participants had been X-rayed because of pelvic problems (pain), but none had any bone or muscle-related problems. All the trans men in this study had been on testosterone for up to ten years and had started in their early twenties. The authors also controlled for age because of how the skeleton changes with age.

Results? The trans men in this study had pelvises in between those of the cis men and cis women. Some features were typical of cis male pelvises, others of cis female pelvises, while others were in the middle. The human skeleton is thought to be stable in shape once puberty is complete. The authors think that the pelvis shape was masculinized during prenatal development rather than by adult hormone therapy.

I’m not entirely sure I agree with their conclusions. I suspect that having trans men who had been on testosterone was a methodological mistake. While the authors can logically argue that hormone therapy did not affect the results, they can’t prove it with data. I think this study needs to be repeated with trans men who have not been on hormones as well as those who have. Differences between their pelvises could be examined, and we could know for certain whether testosterone had an effect.

The authors also attempted to predict the sex/gender for their participants based only on pelvis measurements. They were able to correctly identify nearly all their participants. Only one participant, out of 72, was miscategorized. This could be useful for identifying remains in the future. I’m not convinced, but it’s an interesting idea. I do have some ethical concerns though; could this lead to wanting to use pelvic measurements for diagnosis? I hope not.

It’s an interesting study, and certainly does appear to support the biological theory for the cause of transsexuality. I hope it’s replicated and expanded soon.

Article (Archives of Sexual Behavior)

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