Is modeling humanity as finite really the right way to go? There's always a stream of new humanity coming in, and old humanity dying off. Not to mention the way

Is modeling humanity as finite really the right way to go? There's always a stream of new humanity coming in, and old humanity dying off. Not to mention the way you change as you age- even if you're maximally smart at 16 (which everyone is, of course) eventually you won't be.