Gracile Human Bones (VIDEO) Penn State This video is under embargo. Please login to access this video. Caption This is an interview with Tim Ryan, associate professor of biological anthropology and information science and technology, Penn State on how continuous exercise and mobility make primate bones, ancestral human bones and human forager bones robust, while most modern humans have lighter, more gracile bones. Credit Curtis Parker, Penn State Usage Restrictions Non commercial use only 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.