Population size isn't much of a concern right now so idk what OP is talking about, but I doubt population size is solved. Natural selection, in absence of prema

Population size isn't much of a concern right now so idk what OP is talking about, but I doubt population size is solved. Natural selection, in absence of premature death, selects for those that give birth the most. So while at the moment, we are in a sort of lull, eventually the people who have a low birth rate, will be selected out of the population. The only way this doesn't happen is with another force acting in the opposite direction. For example, maybe whatever is causing the birth rate decline now, actually counters the incentives of natural selection over hundreds or thousands of years, or the population exceeds the carrying capacity of the Earth such that premature death becomes common once again.