I had an idea of a concept a while ago.

If a planet that for some reason or another had only one giant continent like Pangea, but bigger, for more distinct habitats and giant lakes assuring isolation between living organisms.

If humanoid and sapient species starts to develop like our ancestors and us, the pressure for natural selection would be far higher than it was with us, because they still can meet guaranteeing plenty of conflicts to happen, like Neanderthals and our species.

After a whole lot of time, don't know how much, nature greets us with a humanoid species that when push comes to shove can always reproduce if there is too little of one sex or another some of them starts to express the right genes changing to suit the right need.

Of course, in my opinion, this species eradicates the others and because they can always reproduce their genetic diversity and number of adaptations to specific habitats is on a whole other level.

My question is if there is proof of concept to my logic

My mistake, sorry.

PS - The individuals of my species have both internal sexual organs but only in a crisis does their genitalia changes somehow. They don't have sexual dimorphism as we do, height, total mass, muscle mass, fat percentage, etc. Are more related to habitat adaptation then sex.

  • $\begingroup$ Welcome to the site Erick Silveira, please take the tour and read up in our help centre about how we work: How to Ask What do you mean proof of concept? At the moment the only species that we know to be dominant of a planet is (arguably) humans, and our (natural) reproductive strategies are extremley limited. What sort of an answer are you looking for? $\endgroup$ Commented Apr 13, 2019 at 19:35
  • $\begingroup$ Welcome to Worldbuilding.SE! We're glad you could join us! When you have a moment, please click here to learn more about our culture and take our tour. You might want to read our Meta post about "what are you expecting?" questions. We have no real-life datapoint to support any answer yes-or-no and you can choose to make this happen due to "narrative necessity," which is a fancy way of saying, "if you want it to, sure." (*continued*) $\endgroup$
    – JBH
    Commented Apr 13, 2019 at 20:06
  • $\begingroup$ Thanks, though, for using the reality-check tag. That helps as it requires respondents to justify their opinions (and those should be interesting to read). $\endgroup$
    – JBH
    Commented Apr 13, 2019 at 20:07
  • $\begingroup$ "Biological gender" is called "sex". Gender is the social construct, it controls whether a person is called Mr. or Ms. Sex is the biological attribute, it controls whether the person begets children or gives birth to children. $\endgroup$
    – AlexP
    Commented Apr 13, 2019 at 21:20
  • 1
    $\begingroup$ "The individuals of my species have both internal sexual organs": in humans it is not only the sexual organs which are different between men and women. The skeleton is manifestly different in shape and structure (both for the obvious reasons and for reasons which are not fully understood), to the extent that a forensic anthropologist can often tell the sex from a little piece of bone; the distribution of body fat is different; body hair is different (look a photograph of a man and a woman taken against the light) and so on. So it's a question of how human-like the humanoids are to be. $\endgroup$
    – AlexP
    Commented Apr 13, 2019 at 22:20

1 Answer 1


What you are talking about is called sequential hermaphroditism

This is most common in fish and plants, but there is nothing that makes this "impossible" for humanoids, except that we didn't evolve this way.

It's important to note, however, many things change with sex. For humans, having an XX or XY pair of chromosomes provides an advantage. For example, women can evolve with slightly larger hips for child-rearing, men with more testosterone for defending the women during a nine-month pregnancy, et cetera.

This is part of the reason, most likely, as to why we predominantly see this exist in fish and plants: they don't have live birth, and they often expel/inseminate multiple seeds or eggs at one time. With humans, we typically gestate and give birth to one being at a time.

If you lay eggs, it changes the attachment and necessity of offspring; if you have men that can grow children in some otherwise unused uterus-equivalent, then that makes the social group of humans more vulnerable to other animals (or warring countries) - especially in the later months of pregnancy.

So yes, it is possible for a creature to change sex as needed by the social demands, but it's important to note this changes some of the distinctions between the sexes, the evolutionary timeline, and the view they have on children, culture, religion, etc.


In response to an updated question, species born with both genetalia are hermaphrodites. The rest of my answer should still apply.

  • $\begingroup$ Thanks for your answer, but what I had more in my mind was that all humans of my species are born with both internal sexual organs like an intersex person and only when in a crisis like too few men or woman, their genitalia changes. It's my mistake, and I will add this to my question. $\endgroup$ Commented Apr 13, 2019 at 21:49
  • $\begingroup$ @ErickSilveira what you are talking about are hermaphrodites. I've updated my answer, but most of the issues with hermaphrodites are the same for sequential hermaphrodites. There's nothing that says a humanoid species couldn't be predominantly hermaphroditic, but a specific type of sub-variation that expresses one way or the other, except during stress/social pressure/etc $\endgroup$
    – cegfault
    Commented Apr 13, 2019 at 22:25
  • $\begingroup$ Oh, I didn't know, thanks. $\endgroup$ Commented Apr 13, 2019 at 22:41
  • $\begingroup$ @ErickSilveira We have a "sandbox" that you can use to help develop a question, care to take a look? (My opinion, it looks messy on the surface, it's fine and effective): worldbuilding.meta.stackexchange.com/questions/656/… $\endgroup$ Commented Apr 13, 2019 at 23:33

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