It’s too late and I can’t wrap my head around it. Is there some effect from what the deaths and births are? As in it’s not necessarily old people dying and not all births are female which would then further impact the fertility rate?

I understand that the 2.1 replacement rate needed is assuming no migration. There will almost always be migration though.

I think I need to sleep and stop trying to understand this

[–] exocrinous@lemm.ee 2 points 9 months ago (1 children)

Low fertility rates mean the death rate will be higher than the birth rate in the future. But not necessarily right now.

Imagine I build 100 robots, who will each live precisely 100 years. One robot chooses to build a replacement for itself, the rest do not. For 100 years, the death rate will be 0, and the birth rate will be 1. So more births than deaths. But the fertility rate is 0.01, so in 100 years the first generation will all die. Today the birth rate is higher, but low fertility means it'll be lower eventually.

[–] Dave 1 points 9 months ago

Thanks! Like @eagleeyedtiger@lemmy.nz, I think I just needed some sleep.