Prof Grayling is a professor of philosophy at Birkbeck College, University of London, and a fellow of St Anne's College, Oxford.

BBC: Richard Dawkins

"There would be a long way to go before these fads could be said to be anything more than just fads, " says Dr Helen Barrett, developmental psychologist and research fellow at Birkbeck College, University of London.

BBC: Why do people dress up their pets?