Herodotus on Babylon:
They have no physicians, but when a man is ill, they lay him in the public square, and the passers-by come up to him, and if they have ever had his disease themselves or have known any one who has suffered from it, they give him advice, recommending him to do whatever they found good in their own case, or in the case known to them; and no one is allowed to pass the sick man in silence without asking him what his ailment is.
Suroweicki’s book, like this example, was actually about the wisdom of passers-by (unconnected individuals) rather than crowds.
Thanks to David Cramer.