Credit? Screw credit, that's not what I'm talking about. By accident, good ideas wander into our minds and make us smart. OK, there's some amount of positive feedback in this process (ideas about how to accumulate more good ideas). But "ignorance" means being uninformed, that is, not lucky enough to be inhabited by many of these good ideas in the first place. And there's a lot more of them floating around in modern times, and so it's harder to be ignorant, and easier to be lucky, and well-informed, and since ideas help with being a smarty-pants, it's easier to stumble into being smart. Thus ancient people were stupid, in a manner of speaking.