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
Oysters and fish do not have a uterus.
For those that change sex under certain conditions, such as clownfish, they are essentially born hermaphrodites, with hormonal changes controlling which set of organs are active.
That is, the dominant fish in a group has their ovaries activated, while their testes stop. You see similar dominance-based hormonal changes in other animals (such as gorilla), but they activate different processes (such as loss of hair pigment).
Because they’re not human.
A human can’t grow a womb just by producing some hormones, a fish can.
EDIT: Well, not a womb, it’s a fish, but you know, whatever fish parts a fish mommy needs.
This is just something they have evolved to do, while we have not.
The tech we have today is nowhere close to offering the same level of sex change that these animals are capable of. At best, we can alter hormones and perform surgeries that result in the mimicking of the opposite sex’s phenotype. Eventually, tech may allow complete and safely reversible sex change. At that point, changing your sex may be akin to getting a haircut.
It’s kind of how some animals can regrow limbs. Current tech can’t, but prostheses are a thing we can do, and this can mimic some (but not all) of the functions of the lost limb.
Efit: if you’re looking into specifics, their bodies develop in such a way where switching is easy and they keep this qbility for most of their lives, for humans, we generally lose the ability to switch easily at around 6 weeks of gestation.
ELi5 – some organisms can be boys and girls at the same time, sometimes they make themselves babies. Some do asexual reproduction.
**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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