The Wisdom of Crowds by James Surowieki

I've just started this but it seems like a fascinating book (with lots of case studies which I like). Here's a quote from the website about the book:

"In this endlessly fascinating book, New Yorker columnist James Surowiecki explores a deceptively simple idea that has profound implications: large groups of people are smarter than an elite few, no matter how brilliant—better at solving problems, fostering innovation, coming to wise decisions, even predicting the future".

I don't quite understand how this would be, but perhaps somebody mathematically-minded will be along to explain it (if it can be explained by maths). I'm prepared to be convinced by examples though.