Hybrid extremes (IMAGE) Stanford University Caption Two hybrid male swordtail fish representing the extreme versions of the trait these researchers studied. The male on the left has melanoma and the male on the right has only a small spot. Credit Daniel Powell Usage Restrictions Image may only be used with appropriate caption or credit 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.