Can Humans Change Sex?

Description

Some vertebrates like clownfish can change their sex depending on environmental conditions, but can humans?

Sources

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Baldassarre, M., et al. (2013). Effects of long-term high dose testosterone administration on vaginal epithelium structure and estrogen receptor-a and -b expression of young women. International Journal of Impotence Research, 25, 172-177.

Casas, L, Rey-Saborido, F., Ryu, T., et al. (2016). Sex change in clownfish: molecular insights from transcriptome analysis. Scientific Reports, 6.

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Transcript

In the sheltered reefs of the Pacific Ocean, clownfish can change their sex from male to female at a moment’s notice. When a female of the group dies, the fertile male, who used to receive orders from the female, begins to dominate and lead the juvenile males.

But this goes far deeper than a behavioral change. Originating inside the male’s brain, new hormonal signals are sent from the hypothalamus to the pituitary, and then finally, to the gonad. Currently, functional testes tissue resides here. But there is also dormant ovarian tissue ready to be activated. When the gonadal tissue receives these signals, the expression of certain genes are altered and the testes degenerate and are absorbed. Yet the ovarian tissue, having waited long enough, proliferates and becomes fertile with eggs. The transformation is now complete (Casas et al. 2016; Khoo et al. 2018).

It may come as a surprise to some, but humans cannot do this. We are not as plastic as clownfish (Aztekin & Storer 2022; Nagahama et al 2021). Even if we alter certain genes or change hormone levels, fundamental anatomy that has already developed won’t just reverse its development or turn into something else. Once our reproductive system has differentiated in the womb, there is no returning to that undifferentiated, bipotential state. Like 95% of other animal species, humans are gonochoric, which means we are male or female for life (Muyle et al. 2021; Holub & Shackelford, 2021; Pla et al 2022).

While we are not clownfish, this beautiful fish does provide us with a good measure as to what it would mean for a human to change sex.

To understand this, you might ask: when does it become clear that the male clownfish is now a female? It’s not when his behavior changes. Nor is it when his hormones began to change. Instead, it’s when the gonad reorganizes to the opposite sex type: complete ovaries from functional testes. His entire reproductive system transforms from a male one into a female one (in other words, from the body plan that produces sperm to the body plan that produces eggs) [Lehtonen & Parker 2014; Scharer 2017; Goymann et al. 2022]. Like in clownfish, this is the condition required for humans to change sex.

To explore what this process would look like in humans, let’s consider a theoretical example in a male. First, the expression of the entire genome would have to change. Second, the testes would transform into ovaries able to produce eggs. This is the technical point at which sex has changed, the switch of the gonad and its gamete type. To complete the process, the hormone environment from the ovaries would then degenerate the internal and external male genitalia and build the female genitalia. The gene expression required for this would affect the entire body, and the whole sexual phenotype would be transformed. This would all have to be controlled by a level of genetic and phenotypic plasticity that does not exist in humans.

Some argue that taking cross-sex hormones counts as changing sex. While cross-sex hormones can alter secondary sex characteristics like breasts, facial hair, or fat distribution, no amount of hormones can transform a male reproductive system into a female one, or vice versa. At most, these hormones mimic the effects of endocrine disorders. For example, human males on cross-sex hormones experience testicular regression with severe cellular damage and penile atrophy (Cheng et al. 2019; Leavy et al. 2017). Females on cross-sex hormones develop pathological ovarian morphology (Cheng et al. 2019) and vaginal atrophy (Baldassarre et al. 2013). This is not changing sex. It’s just damaging the body.

Others argue that genital surgery counts as changing sex, but this is a mere alteration of appearance. The tissue itself is not transforming into that of the opposite sex. It also leaves severe and permanent harms, rendering those sex organs non-functional.

Humans are not clownfish. Our bodies are much more complex, and our sex is determined by genetics in the womb and fixed for life. Like all mammals, we cannot change our sex. But we shouldn’t view this as a problem. Instead, we should learn to accept and appreciate this fact for the health of our bodies and minds.

Reality is that which, when you stop believing in it, doesn’t go away. –Philip K. Dick

END

© 2024 Zachary A. Elliott, All Rights Reserved.

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