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"Most people have heard of natural selection," says lead author Kang-Wook Kim at the University of Sheffield. "But 'survival of the fittest' cannot explain the color diversity we see in the Gouldian Finch. We demonstrate that there is another evolutionary process -- balancing selection -- that has maintained the black or red head color over thousands of generations."
The yellow-headed type (actually more orange) is produced by a completely different mechanism that is not yet understood. Yellow-headed Gouldian Finches make up less than one percent of the wild population.
Color - Types - Polymorphism - Species - Time
"Having distinct multiple color types -- a polymorphism -- maintained within a species for a long time is extremely rare," explains co-author David Toews, who did this work as a postdoctoral researcher at the Cornell Lab and who is now at Pennsylvania State University. "Natural selection is typically thought of in a linear fashion -- a mutation changes a trait which then confers some reproductive or survival advantage, which results in more offspring, and the trait eventually becomes the sole type in the population."
Studies from Macquarie University in Australia have shown the red-headed finches have the apparent advantage. Female Gouldian Finches of all colors prefer the red-headed males, who also happen to be more dominant in the social hierarchy. So why hasn't the black-headed type disappeared? It turns out there are disadvantages to having a red head, too, such as higher levels of stress hormones in competitive situations.
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