[robocat]

Our lovely residents of Binary Town keep their average birth rate at 2 through enlightened and fair methods.

Then Professor Gemini discovers a cure for cancer, which doubles their lifespan.

Unfortunately very soon they are having an unexpected housing shortage.

How did that happen?

[TangoTrotFox]

Sure if you create an absurd example of suddenly doubling every single person's life expectancy you can start to see some impact from changes in such, but in reality this does not happen. Life expectancy changes extremely slowly, and it also goes in both directions on a worldwide scale further mitigating any effect on population levels.

It's like Big O in a way. Adding some stuff to O(1) doesn't really matter compared to something that's O(n^2) except when start adding some really really unreasonably huge things, though even there n^2 tends to catch up really fast. In either case it's not a practical issue in code or population.