PS: The last man would not have had a lot of sex, because at that point they would already have come up with a way to reproduce among women.
Actually ch 1.1 is quite explicit that the breakthrough(s) allowing female-female reproduction postdated the death of the last known male H. sapiens sapiens. I elaborated a rough overall timeline of the whole business way back when, but short form here is that they must've been getting pretty desperate by that point as most of the female population would have been fast approaching (or was already past) menopause...
Here is the thing: I don't care about your timeline.
Here is the thing: it computes and trying to discuss an alternate history without at least a basic timeline of events essentially amounts to randomly pulling shit out of your ass while groping blind. You're welcome to work out an alternative ofc but I can't really see it coming down to anything dramatically different, given it largely derives from the biological realities of human lifespan and reproductive fertility.
So anyway, the phrasing is a bit odd in those two pages. I don't necessarily think she meant that they developed that method after the last man died in 1920. The "after that" could also refer to the recognition of the virus' existence.
*le shrug* By far the single most obvious and natural interpretation of the teacher's lecture is taking it at a face value. I'm just going by what the author states in plain text about the setting, man.
Giving the author the benefit of the doubt here of course, because there is no way no research would have been done by the early symptoms of male population decreasing more and more for decades.
Of course they did, once people started noticing the phenomenom. But that'd have been circa mid-1800s or so when the relevant sciences were either at their infancy or didn't yet even exist and the kinds of tools needed to actually closely study, nevermind now manipulate, molecular biology were even worse off (or rather more specifically, over a century off in the future behind considerable advances in other fields). Throw in the diverse serious disturbances caused by the rapid aging and depletion of the suddenly unreplenishable male population (hithero the de facto ruling sex and more prosaically primary labour pool) and peoples' reactions to the whole business and we're talking about a truly daunting uphill struggle indeed.
At least we agree that they must have been desperate. I don't even want to imagine that kind of pressure.
As mentioned, "medical ethics" ought to have been out of the window a long time ago by that point. Probably safe to assume the tech got rushed out of the labs as soon as it was even vaguely functional and Devil take any side effects - they had survival of the species riding on restarting human reproduction ASAP after all. No doubt any number of medical horror stories occurred before the inevitable bugs were worked out by trial and error but eh, desperate times.
