Watch NOVA Season 33 Episode 18 Online

This episode focuses on a scientific debate about five siblings in a Turkish family who walk on all fours. When, in 2005, scientist Uner Tan labeled them "genetic throwbacks," they became part of the dialogue about a possible missing link to an era when humans walked on all fours. Included: comments from geneticist Sean Carroll and anthropologist Brian Richmond, who disagree with Tan; and interviews with and footage of the family.