Scatterplot (IMAGE) Salk Institute Caption Hammerhead sequences copied by the lower-fidelity polymerase drift away from their original RNA sequence (top) and lose their function over time. Hammerheads catalyzed by the higher-fidelity polymerase retain function and evolve fitter sequences (bottom). Credit Salk Institute Usage Restrictions With credit and related coverage 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.