This past weekend, I watched a TV movie from 1994 called "Island City" – a post-apocalyptic science fiction tale where an eternal youth drug had worked for some humans, while mutating many others into immensely strong and violent primal brutes. Many of the former live in a protected city, sending patrols to find other "normal" living among the brutish "recessives" in the "badlands" beyond. To avoid giving birth to more potential recessives, every adult inhabitant of the city has a special colored crystal implanted on their chest, and is only allowed to have sex with someone with the same color.
Forget how simplistic and gimmicky it seems, or that we're now beginning to understand the complexity of human genetics. Such a "solution" ignores the realities of human psychology. Did the writers of this story really think that everyone would just say: "Well, I like you, but I'm a green and you're a blue, so no dice"? Yeah, right.
It reminds me of a similar shortcoming in the Star Trek: Enterprise episode "Cogenitor" – an alien species treats members of its third sex as mere means to the end of procreation, depriving them of choices and education and even personal names. Imagine being the parent of such a child, wondering why they shouldn’t be able to make more of a contribution than simply being "assigned" to one couple after another. And as the series Alien Nation demonstrated in its storyline, it's not impossible to conceptualize a more respected social role for cogenitors.
As Isaac Asimov pointed out, a good science fiction writer must know science, and I would contend that this includes the so-called "soft" social and behavioral sciences. Human beings ultimately questions rules and find ways to work around the diverse barriers put in front of them. That is especially true when it comes to sexuality and intimacy. We may seek to find and create some rational and orderly way of choosing mates and expressing affection, but ultimately such decisions are impelled by passion and desire, even to the point of affecting what we perceive to be "rational and orderly".
There is no better real-life example than the disagreement over the hypothesized invention of "sexbots" for erotic release. Proponents see the potential for custom-made sexual partners, perhaps even doing away with sex trafficking and prostitution. Those opposed to this hitherto nonexistent technology, such as British academic Kathleen Richardson, speculate that the "unequal power relationship" between humans and robots would somehow bleed over into relationships between humans as well. Both extremes are to be congratulated for pushing the envelope of imagination, yet they do so by blithely ignoring the realities of technology, materials science, economics, and sexual psychology. Assuming that sexbots were to become a reality, it follows that they would be incredibly expensive, prohibitively so for most mere mortals. And while things like transportation and cleaning are made more efficient with cars and washing machines, erotic satiation and fulfillment demand a complexity and nuance which no artifice has come close to meeting.
Sex, like much of human and animal nature, is chaotic. That may not sound very scientific, and yet science has its own definition of chaos: sensitivity to initial conditions. Each individual is indeed sensitive to the conditions surrounding us, from birth to death, and no more so than when we interact with those around us. We may develop social and cultural structures to help us navigate, and science may provide data and insight, but in the end the course we take is our own choice to make.