Genetic Switch With an Ancient History (IMAGE) University of Chicago Medical Center Caption Genetic instructions for developing limbs and digits are shared by species separated by 400 million years of evolution. Credit Kalliopi Monoyios, University of Chicago Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.