It is possible that the many, no one of whom taken singly is a sound man, may yet, taken all together, be better than the few, not individually but collectively, in the same way that a feast to which all contribute is better than one supplied at one man’s expense. […]
There is this to be said for the many. Each of them by himself may not be of good quality; but when they all come together it is possible that they may surpass—collectively and as a body, although not individually—the quality of the few best. […]
Provided the mass of the people is not too slave-like, each individual will indeed be a worse judge than the experts, but collectively they will be better, or at any rate no worse.

Aristotle on Collective Intelligence, Politics, circa 334-23 BC. 

a bunch of Aristotle quotes here, hat tip to Cass Sunstein