Yellow warbler (IMAGE) Penn State Caption The research team found that one color-related gene has undergone a standard mode of evolution, with mutations arising in separate species. By contrast, portions of the second gene in some cases have been transferred between species through a process known as introgression, where hybrid birds mate with a parent species and, over generations, transfer genetic material. Credit Todd Fellenbaum Usage Restrictions Credit must be provided 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.