Adam Gopnik tries to rationalise what lies behind his new obsession - of walking 10,000 steps every day.

With the help of his daughter, Darwin and the Cynics of ancient Greece, Adam concludes that, in our search for meaning in life, 'meaning bound around by a number is easier to grasp than meaning left to meander where it will.'

'The act of taking 10,000 steps a day,' he says, 'brings with it a sense of conscious accomplishment that the phrase "a good long walk" cannot'.

Producer: Adele Armstrong Sound: Peter Bosher Production coordinator: Gemma Ashman Editor: Richard Fenton-Smith