The Royal Institution, London Annual Christmas Lectures to Young People by Dr John Napier

We know the great differences between walking on two legs or on four legs. Human walking is a risky business and depends on split-second timing and balance. Without this we would fall flat on our faces. Four-legged creatures are infinitely safer.
Apart from exploring the advantages of bipedalism as a way of life, Dr Napier examines with members of the audience the characteristic human walking pattern of striding.