I don't believe there are exactly two biological sexes
I don't want to get essentialist on you, but I think this confuses gender and sex. To make a human being, you need an egg and a sperm. Right now, there are some folks with eggs and some with sperm. That's biological. Gender-wise, there may be multiple genders and that's cultural. But biologically, human beings still have two sexes.
[It's true that there are some folks, though the numbers are very small overall, who have some of all of the organs of both sexes and then have to sort it out further, but again, that's not, shall we say, usual.]
The folks with the eggs have the sperm enter their bodies from the outside in some way and then the fertilized egg grows within them. The other folks do not. And despite all the Mpreg stories popular in fandom, males do not conceive nor carry babies. They don't have the equipment.
The folks who have the equipment (and there's a lot of equipment if you count everything that, evolution-wise, is needed to not only have but raise a helpless infant to adulthood) will be at some disadvantage because having and raising a child takes time and effort. Culture might shift that effort to someone or something else, but it will take time for evolution to then lose the traits necessary for having and raising children.
As a mother myself (who came to it old, late and not completely voluntary) I can tell you that biology is fierce when it comes to parenting, especially motherhood, and even if I could pass my child around for care, I don't know how much I would or could. There's a reason for that, and it's only partly (and probably a small part) cultural.
no subject
I don't want to get essentialist on you, but I think this confuses gender and sex. To make a human being, you need an egg and a sperm. Right now, there are some folks with eggs and some with sperm. That's biological. Gender-wise, there may be multiple genders and that's cultural. But biologically, human beings still have two sexes.
[It's true that there are some folks, though the numbers are very small overall, who have some of all of the organs of both sexes and then have to sort it out further, but again, that's not, shall we say, usual.]
The folks with the eggs have the sperm enter their bodies from the outside in some way and then the fertilized egg grows within them. The other folks do not. And despite all the Mpreg stories popular in fandom, males do not conceive nor carry babies. They don't have the equipment.
The folks who have the equipment (and there's a lot of equipment if you count everything that, evolution-wise, is needed to not only have but raise a helpless infant to adulthood) will be at some disadvantage because having and raising a child takes time and effort. Culture might shift that effort to someone or something else, but it will take time for evolution to then lose the traits necessary for having and raising children.
As a mother myself (who came to it old, late and not completely voluntary) I can tell you that biology is fierce when it comes to parenting, especially motherhood, and even if I could pass my child around for care, I don't know how much I would or could. There's a reason for that, and it's only partly (and probably a small part) cultural.