Every park has at least one weird duck. It’s the wrong colors—all white, or patchy white; its bill bright storybook orange or its face weirdly red and lumpy. Next to the other ducks it looks oversized and bulky, like a linebacker in a crowd of quarterbacks.
How new species form, and what determines whether they last, is one of the major topics in evolutionary biology; and much of this topic is embodied by that one weird duck.
Tough Little Birds 