Follow TV Tropes
> In "The Deadly Mission of Phineas Snodgrass", a deconstruction of Lest Darkness Fall, a man goes back in time to the Roman Empire and brings them modern knowledge until a thousand years later the Earth is so overpopulated that the future sends someone else back in time to kill him just as he arrives in Roman times
This makes no sense. The same forces that are pushing population growth to zero, or in some places actually negative, would apply to this alternate universe as well. In fact, they'd have it easier because they'd achieve high technology with a lower initial population, having been handed all that knowledge in one go. There'd be an initial population boom as infant mortality drops to sane levels, then a leveling off as people switch childrearing modes from quantity to quality. For example, I don't think the world population in S.M. Stirling's ISOT trilogy will ever exceed a few hundred million.
The only way they'd keep breeding like rabbits would be if there was some kooky religious cult that held absolute power and forbade things like contraceptives, had a "lots of kids" fetish, and was basically dead set on keeping women barefoot and pregnant in the kitchen. And if that approach actually worked, then old-school Mormons, fundamentalist Muslims and Catholics, and Nazis would rule the world.
Community Showcase More
How well does it match the trope?