Why is a big word - well, it isn't, but you know what I mean - and it's one that BBC World Service presenter Mike Williams has been asking for a couple of years now in his series The Why Factor (BBC World Service, 7.30pm).

Among the questions he has pitched into the ether are "Why do we wear ties?", "Why do we lie?" and, possibly the hardest to answer, "Why do we behave so oddly in lifts?".

On Friday, he wanted to know why we go on long walks.

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It was a question which involved a smattering of psychobabble - "It's about going inwards," said one interviewee; "Walking made us human," said another - but it also brought mention of philosophers Jean-Jacques Rousseau and Arthur Schopenhauer and a great deal of thought-provoking asides from people such as Jo Vergunst, a social anthropologist at the University of Aberdeen and Philip Oltermann, the author of Keeping Up With The Germans.

Vergunst talked about the simple pleasure of the rhythm of walking and about how much more easily differences can be resolved if participants walk abreast rather than stand in confrontational opposition. Suddenly those shots of off-duty world leaders strolling across well-manicured lawns together as they try to solve the world's ills start to make sense.

From Oltermann we learned that in Germany, walking is ingrained in the culture and has been since the Romantic period when wandering became what he called "a key motif".

Of course, where there is psychobabble there is also usually Will Self, and so it went here. "I've always walked," the author told Williams, while musing on his feelings of claustrophobia, of being trapped in "a virtualised topography", whatever that is.

But elsewhere Self was full of insight about the act of walking and brought no small amount of humour to the subject as well.

"Isn't walking a rejection of modernity?" asked Williams at one point, to which Self replied with a story about trying to walk to Heathrow airport and eventually running out of pavement and being faced by a sign which said: "No pedestrian access - go back to The Renaissance".

The Renaissance turned out to be a hotel.