Do some dogs have a built-in GPS? Dr. Hare explains how dogs use a sensation of the earth's magnetic fields to hone in on where they're going. Two top experts in the field of canine navigation discuss why some dogs get lost and others always manage to find their way home. Featured Guests: Dr. Evan MacLean, Assistant Professor, School of Anthropology at the University of Arizona; Dr. Alexandra Rosati, Assistant Professor, Department of Human Evolutionary Biology at Harvard University.