If I had to guess, compared to other primates it takes human young too long to be any good for anything. Permanent breasts would make cross-nursing more feasible in the event that a mother died or couldn't produce enough during scarcity.
No sources or background, just throwing darts at a plausible "the ones who didn't died" scenario.
> Permanent breasts would make cross-nursing more feasible in the event that a mother died or couldn't produce enough during scarcity.
I don't understand what you're trying to say here. Most mammals do fine with nipples and no breasts, whether they're nursing or not. And women lactate after giving birth; they can't do it on command.
On the other hand, it doesn’t seem to be “oh no nudity” if a woman wears a very skimpy bra that only covers their nipples and fully exposes the rest of their breasts.
No sources or background, just throwing darts at a plausible "the ones who didn't died" scenario.