Carl, one of the root assumptions here is that infants are much cheaper to produce than preteens are to feed. The Babyeater children are eliminated at just the stage before they begin quickly growing and consuming lots of food (but not, alas, before the stage before they become sentient). If most of the total cost of growing a child lies in feeding it past the rapid growth stage, rather than birthing 50 infants and feeding them up to that point, then tribes that birth fewer infants will not have much of an advantage. It’s even possible that the reduced selection pressure (weeding out poor immune systems, dumb kids, etcetera) would become significant at this point in terms of both individual and group advantage.
Furthermore, to the question “Why didn’t evolution make improvement X?”, “It just didn’t” is often a pretty good response. The mutation you postulate does involve more than one change—even if the Babyeaters seem well-predisposed to it in terms of preadaptation, it might just not happen. You’re also postulating that a whole group gets this mutation in one shot—but even if you say “genetic drift”, it seems pretty disadvantageous to a single invader. They’ll just suddenly classify a bunch of others as evil, and so be cast out themselves.
Richard, I’d take the black holes of course.
Carl, one of the root assumptions here is that infants are much cheaper to produce than preteens are to feed. The Babyeater children are eliminated at just the stage before they begin quickly growing and consuming lots of food (but not, alas, before the stage before they become sentient). If most of the total cost of growing a child lies in feeding it past the rapid growth stage, rather than birthing 50 infants and feeding them up to that point, then tribes that birth fewer infants will not have much of an advantage. It’s even possible that the reduced selection pressure (weeding out poor immune systems, dumb kids, etcetera) would become significant at this point in terms of both individual and group advantage.
Furthermore, to the question “Why didn’t evolution make improvement X?”, “It just didn’t” is often a pretty good response. The mutation you postulate does involve more than one change—even if the Babyeaters seem well-predisposed to it in terms of preadaptation, it might just not happen. You’re also postulating that a whole group gets this mutation in one shot—but even if you say “genetic drift”, it seems pretty disadvantageous to a single invader. They’ll just suddenly classify a bunch of others as evil, and so be cast out themselves.