Is simultaneous hermaphrodite species stable?

Question

I'm writing a story set in the after the end world scenario. The very few humans who survived the apocalypse in the facilities deep underground, decided that human race is too self-destructive and violent. So while waiting for radiation levels to drop they've genetically engineered a new humanoid species of simultaneous hermaphrodites. The hermaphrodites are human females with additional functional male sex organs, like futanari from anime. Fast forward a few centuries in the future and humans are extinct, nature took over the remnants of human civilization like in Life After People. The hermaphrodites are the most intelligent beings on Earth. They live in tribes and their technology is on the level of the native North Americans before the contact with the Europeans.

Would the new species stay hermaphroditic on their own?

I'm afraid that stronger and more violent will specialize in being males, while weaker will specialize in being female, and in few generations there would be two sexes again.

As per my understanding of evolution, please correct me if I'm wrong, all it's needed is that hermaphrodites who specialize of being males have better fitness then egalitarian ones. Then their numbers will grow until they get to 50% when the rest will simply specialize in being females since that's the more rare sex.

I'm hand-waving how the humans genetically engineered the hermaphrodites. I assume they had knowledge and resources to do it. However those things are gone in the present of my story.

Answer 1

There is little reason to assume that your hermaphrodite humans would not be stable.

It is possible that individuals might choose to take roles in society which are associated with stereotypical male or stereotypical female behavior in our society. After all, your society will need stereotypically male specialists like blacksmiths, lumberjacks, hunters, leaders and (if they are warlike) soldiers. But considering that there are no objective physical characteristics which clearly state that one belongs into a male or a female role, there is no inherent reason why any individual would be pressured into taking a specific role. There is also no reason why anyone would still think in categories like feminine behavior or masculine behavior.

It might be possible to introduce a caste system with some castes being expected to behave stereotypically male and other castes to behave stereotypically female. But there is no reason to expect that such a caste system would be a logical conclusion. You don't need one when you don't want one.

I'm afraid that stronger and more violent will specialize in being males, while weaker will specialize in being female,

If this is the case, then it would be reasonable to assume that the more masculine people feel sexually attracted to the more feminine people and vice versa. So the masculine and feminine genes would constantly crossbreed, leaving no chance for either trait to stabilize.

Those traits would only stabilize if people with these traits feel sexually attracted to people with the same traits (butches being into butches and femmes being into femmes). Keep in mind that in order to be fertile, these gender roles must not strictly extend into their sex life. If both partners in a relationship prefer to penetrate or both prefer to get penetrated, they won't have much genital sex at all. But the more interesting question is if such partnerships would provide an evolutionary advantage over the more heterogeneous partnerships where the partners complement each other or not. This creates some interesting questions which also have parallels to our society, namely the debate about adoption rights for homosexual couples. This might be an interesting concept to explore in detail in your work of fiction.

Answer 2

Gender is a social construct. The way males and females act differently from each other is mostly arbitrary. We can look through different societies and see that masculine and feminine social roles and behaviour can be completely different from how we have them in our society. From when we are born we are pressured to act in certain ways depending on what genitals we are born with. But these social roles are arbitrary.

There are some small differences in gendered behaviour because of different hormones. But these are amplified by social roles. But in a society where social roles where not pushed onto people and everyone was brought up similarly the difference in behaviour based on sex would be negligible.

As for the person saying the Y chromosome is the thing that causes men to be more violent, citation needed. That sounds like misandrist pseudoscience they’re pushing right there. It’s testosterone that has an effect on how strong a person is. And may have a small effect on a person’s predisposition towards violence. But it is mainly social roles that lead men to be more violent.

So in a society where it is impossible to pressure people into acting different ways based on genitals, because everyone has the same genitals, people would be more free to act in the ways that make them most comfortable. Some people would choose to present more feminine, and some people would choose to present more masculine. And some people would choose to present more androgynous. There’s no need to have strict gendered roles anymore. People would just act in whatever way corresponds to who they are on the inside.

As for whether or not they’d be genetically stable. It doesn’t matter. This is fiction. If you say they’re genetically stable, then they are. You don’t need to scientifically justify concepts like this in fiction. Just say it works and the reader has to suspend their disbelief. You can do a little justifying if you want but it only needs to be to the extent of the reader getting a basic understanding of how it works. You don’t need to be a biologist to write a story about hermaphrodites.

Answer 3

Simplest solution - kill all the males

You don't really need to do this through extensive genetic engineering, and it will probably happen naturally anyway. And yes, this evolved human form will be very stable. There are analogies in nature.

The Y chromosome in humans is actually very, very small compared to other chromosomes, and particularly useless. It is full of anomalies, that make males much more prone to genetic diseases. Eventually, the Y gene will become so non-functional as to be eliminated completely from the genome.

Sexual differentiation in humans is NOT dependent on the Y chromosome. It is useful for starting the differentiation process, as a trigger for other events, but these events can be triggered by other genes. There is nothing on the Y chromosome itself that is exclusively part of the process, or even that is exclusively needed in the process.

However, by eliminating the Y chromosome, you eliminate a lot of problems associated with testosterone. Particularly, the predisposition to violent behavior, and the predisposition to mental illnesses and mental aberrations that lead to violent behavior. Without testosterone, your evolved humans will be particularly non-violent, even pacifist.

It is not humans per se that are the problems, it is human testosterone-driven after-the-fact ooops-evolution-goofed males. Humans, as first envisioned by the default 'female' setting for humans, the female, are actually quite civilized.

It is no secret that men are basically genetically modified women - the female being the fall-back developmental pathway for any fetus. The evolution of the two sexes could indeed be regarded as a long-running GM experiment. Its legacy has been to endow men and women with different, and often conflicting, sets of genetic interests, and to ignite a powerful evolutionary struggle, which has accentuated the differences between the two sexes. In several respects, the experiment that gave us men is not going too well just now. Though it is a weary lament to lay most acts of violence and aggression, from the strictly local to the truly global, squarely at the feet of men, the association is strong, consistent and undeniable. Women very rarely commit violent crimes, become tyrants or start wars.

https://www.theguardian.com/science/2003/aug/28/genetics.genderissues

So to achieve your results, just get rid of the Y chromosome completely.

Incidentally, getting rid of the Y chromosome would be extremely beneficial to a society living in very close quarters underground. Females have always been much better in close quarters-for-prolonged-periods environments.

And getting rid of the Y chromosome is really, really easy. Just kill off all the males, and induce a reproductive 'male' gender by artificially triggering it using testosterone shots in utero.

Hokkaido University researchers have revealed that key sex-determining genes continue to operate in a mammalian species that lacks the Y chromosome, taking us a step further toward understanding sex differentiation.

from How to be a male without the Y chromosome

Second solution - pure hermaphrodites

To alleviate your concerns, at the time of copulation, the participants decide which will be 'male' and which will be 'female', but only for the length of time of the copulation. Then they return to neutral.

Third solution - the earthworm

The hermaphrodites copulate as both males and females at the same time. Each becomes pregnant, each reproduces. This trick has been used in nature. See for instance earthworms and they have been stable for millennia.