People can change their sexual characteristics with hormone therapy and surgeries, but having the reproductive capacity of the opposite sex is unfortunately not possible; while uterus transplants are theoretically possible, even then, a donor/IVF would be needed because the ovaries wouldn’t have eggs with the mother’s DNA. So how can some animals do what we with all of our technological advancements can’t?
In: Biology
**For fish** (*specifically Teleosts, a group that includes most bony fish and all the known sex-changing fish*) at least, part of why they can do it (and why it’s so common in them compared to other vertebrates), is likely due to a are a couple reasons:
* **In most vertebrates, the ovaries and testes start development in slightly different areas during embryonic development, but in teleosts they form from exactly the same region. This makes it easier for the gonads to switch from testes to ovaries and vice versa.** Also, this means means even in many fish with a “normal” sex system, the juveniles are neither male or female gonad-wise (the source called it “bisexual juveniles”). Also, non functional ovary tissue in males and nonfunctional testes tissue in females can often be found and made to develop in the lab
* The reproductive tracts of most fish are also super simple, meaning they don’t need to turn a penis into a clitoris and grow a vagina or whatever, it’s just a tube from the genitals to the outside world either way.
* Finally, the sex-determination system (what determines what sex an animal ends up being) are diverse and evolve rapidly in fish.
source: [Phylogenetic Perspectives on the Evolution of Functional Hermaphroditism in Teleost Fishes ](https://academic.oup.com/icb/article/53/4/736/634581?login=false#10790902), specifically the section “**Why is sexuality so labile in teleost fishes compared with other vertebrate groups?**”
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