Soay Lamb (IMAGE) Princeton University Caption This lamb is part of a flock of sheep living on the Island of Hirta, St. Kilda, in Scotland. A team of researchers from Princeton University and the University of Edinburgh studied the sheep and concluded that strong immunity may play a key role in determining long life -- but at the expense of reduced fertility. Credit Photo by Arpat Ozgul/University of Edinburgh 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.