But if you were an illiterate random peasant farmer in some historical venue, and you needed to know the growing season of taro or barley or insert-your-favorite-staple-crop-here, Wikipedia would have been superfluous: you would already know it. It would be unlikely that you would find a song lyrics website of any use, because all of the songs you'd care about would be ones you really knew, in the sense of having heard them sung by real people who could clarify the words on request, as opposed to the "I think I heard half of this on the radio at the dentist's office last month" sense.

Everything you would need to know would be important enough to warrant - and keep - a spot in your memory.

I am not sure how different this example here is any different from Googling.

The first time a farmer wants to know something, such as the season to grow a crop in, he taps into the local pool of knowledge available to him. This pool could consist of his father, or the village elders, or the experienced farmer two miles in the neighbouring farm. And he only bothers remembering this factoid about seasons, and whatever else, because it would be a real pain to run two miles each time he wants to do something on his farm, every day. And by the same argument, things he doesn't have to know on a daily basis or can live without, such as that village song, or the latest gossip in town, he will *not * bother committing this to memory. He will wait for the next time they gather around a fire or something to gather the latest. Again consider somebody looking at the man page for the arguments to a system call that she uses on a daily basis, and committing this to memory because it is more optimal to just remember it (because the two monitors she has are only big enough to keep her code windows open) and it would improve her productivity do so. She will *not * bother to commit to memory those calls and their arguments that she doesn't use as often, and will go hunting in the man pages.

I guess what I am trying to say is that our great brains have always been external. There is a bunch of stuff that is local, and there is the bunch that is non-local. The non-local stuff is the collective of stuff that exists in and amongst the people we live with, talk to, our books and now of course the internet. And what is local, a vast majority of it, has always been a subset of that which is non-local. It's only the magnitude of this non-local set that is easily (relatively speaking) accessible that has changed (by orders of magnitude).