Have you ever wondered why humans have a groove above the upper lip that seems to have no purpose whatsoever? This groove, known as the philtrum, tends to go un-noticed unless it is not completely formed, resulting in a cleft palette. With the help of a CGI created from high quality human embryonic scans during the early stages of development, Dr. Michael Mosley shows that the forming of the philtrum is actually a clue to our evolutionary fish ancestry.