They may look the same ... but are they? NOVA explores epigenetics - hidden influences that add another layer to our DNA.Lifetime/Sarah Holt for WGBH - Friday, October, 12, 2007, 10:12 PM

The NOVA runners at the Boston Marathon.PBS/Joel Laino - Saturday, September, 29, 2007, 12:29 AM

Carol Baryboy making her way to the finish line at the Boston Marathon. PBS/Joel Laino - Saturday, September, 29, 2007, 12:29 AM

Betsey Powers-Sinclair at Heartbreak Hill at the Boston Marathon.PBS/Joel Laino - Saturday, September, 29, 2007, 12:29 AM

Jonathan Bush running at the Boston Marathon.PBS/Joel Laino - Saturday, September, 29, 2007, 12:29 AM

Three time Boston Marathon winner, Uta Pippig, cheering on the NOVA runners at the Boston Marathon. PBS/Joel Laino - Saturday, September, 29, 2007, 12:29 AM