If you ask a group of people to guess the value of a painting, the chances are the answer they come up with will be more extreme than that produced by any of the individuals working by themselves.
It's a common psychological effect, verified by experiment, that could lie at the heart of many of the biggest crises to hit in recent years. How did the bankers selling sub-prime mortgages to each other continue to fool themselves that these were genuine investments rather than highly dangerous junk deals? Surely any one of them could have seen the problems they were going to cause? Maybe - but the key point is that they didn't.
The week the Human Zoo explores the mistakes humans make when they act in groups. How apparently sane individuals can make ludicrous and sometimes life threatening group decisions.
The Human Zoo is presented by Michael Blastland, with the trusted guidance of Nick Chater, Professor of Behavioural Science at Warwick Business School.
Producer: Toby Murcott
A Pier production for BBC Radio 4.