Friend for Life: The extraordinary partnership between humans and dogs

Even if we've never had direct contact with one, we will have seen one, or at the very least, heard one. For those of us who live in the western world it is more than likely that one sleeps in our house, possibly even on our bed. I'm talking of course, of the dog. Yet, this animal, which lives alongside five hundred million of us all over the world - as an invaluable partner and a trusted confidant - presents us with one great unsolved mystery: how did this relationship - the most complex and enduring of any between human and animal - start in the first place?