Darwin and Biological Rhythms (IMAGE) PNAS Nexus Caption Watercolor illustration of Charles Darwin. Darwin studied biological rhythms in various organisms and across different time scales, from meticulous descriptions to speculative and experimental investigations. Credit Mateus Andrade Usage Restrictions None License Original 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.