Fitness in a Changing World (IMAGE) U.S. National Science Foundation Caption Different genes code for two different forms of stickleback fish and result in different fitness. Credit Zina Deretsky, National Science Foundation 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.