[trumpdong]

There was a science fiction story I read about that once, an alien species that would die if they didn't give birth every year. I think they tried everything from hormone modification to mass baby dump pits but they couldn't maintain a stable society for longer than about fifty years when overpopulation killed everyone, so thrt just gave up.

Actually more than one, because I also read one about scientists deciphering messages from aliens who used the word for "baby eater" to mean "good"

[Izkata]

The first one sounded familiar and I've definitely read the plot summary of this before, but not the book so I don't know if the rest of that description applies: https://en.wikipedia.org/wiki/The_Mote_in_God%27s_Eye

The other one appears to be https://www.goodreads.com/book/show/15744759-three-worlds-co... (summary and review at https://www.reddit.com/r/CharacterRant/comments/up854p/three... )