> 1000 years ago some subset of people chose not to have children, and humanity did just fine, and that same group of so-called "non-breeders" still exists today.

There have always been, and always will be, people who don’t have kids, for a whole host of reasons.

But that’s not the argument (or at least, not the steelman version of it, as opposed to the strawman one) - the argument is that if there are certain heritable traits that discourage people from having children, then all else being equal, natural selection will cause the frequency of those traits to decline over time, albeit often not to zero.

The all else being equal part is very important. In a society with strong social pressure to reproduce, a trait which makes people less likely to want children may not be strongly selected against - because the social pressure to reproduce means desire to have children only has a small impact on the odds of actually having them - whereas in a society which is much more individualist, it may have much more of an impact, so the selective pressure against that trait may be much stronger. And of course, a trait which produces less desire for children might nonetheless be selected for because it produces some other countervailing advantage

Still, I think the argument does have some weight - that in contemporary Western society where reproduction is far more of a voluntary choice than it once was, biological and cultural factors which encourage reproduction are going to be selected for to a much greater degree than they were in the less individualist societies of decades and centuries past, where less such encouragement was needed

>This is like claiming gay people will "die off" in 2 generations because they don't reproduce.

It's a serious and interesting question as to why evolution tolerated/encouraged homosexuality in a small but significant proportion of the population. If you have the time, this article gives a good overview of the discussion [1].

Depending on your answer to that question - along with your views about how evolution affects modern humans another - it's natural to think about homosexuality will occur in future humans.

Could we have more, less or about the same of it? Will everybody be bisexual? How might medical fertility treatments affect the outcomes? It's an open field of ideas.

[1] https://www.sciencefocus.com/the-human-body/the-evolutionary...

I don't think nature promoted it, but that it is a maladaptive corruption of mating systems which isn't serious enough to result in its cause disappearing from the gene pool.

If evolution is sensitive enough to give us two kidneys via some indirect impact on the number of reproductive offspring we create, why can’t it drive a “software” change to give people the desire to have heterosexual sex?

The best answer I can think of is that sexuality is somehow very fragile for evolution to calibrate, so even natural selection isn’t powerful enough to select heterosexuality reliably.

But it’s hard to argue that persuasively with a biological basis which we don’t yet have.

Compared to the other evolutionary arguments for homosexuality it also doesn’t scale well to other non reproductive sexual behaviours.

Both things must be true.

On the one hand, you'd expect humans (animals) to have completely bred out all forms of infertility -- except that there are non-heritable causes of infertility. (In fact, all causes of infertility must be non-heritable, or at least not inherited! :)

On the other hand, it's surely true that characteristics which deprioritize or diminish the likelihood of reproduction are bred out, however incompletely. Whether it's a sense of taste that enjoys poisons, a risk-taking brain that kicks in before fertility, homosexuality (in males at least), or just not wanting children.

These characteristics are bred down to a sustainable level, obviously. But they are clearly not bred out fully, nor are they consistently bred "up".

> homosexuality (in males at least)

In many traditional societies, there is strong social pressure for marriage and children, arranged and semi-arranged marriages, etc - such that a person’s sexual orientation may not make much difference to their odds of heterosexually reproducing. Some people might enjoy heterosexual reproduction and others might endure it but they’ll do it all the same. So that would limit the selective pressure against genes that increase the likelihood of homosexuality

In the mainstream contemporary West, if heterosexual reproduction doesn’t appeal to you, then you just don’t do it-so selective pressure against those genes may exist to a degree that it formerly did not. On the other hand, the new possibilities for non-heterosexual reproduction (such as IVF, sperm/egg donation, surrogacy) might counteract that.