ABSTRACT
What is an adaptation? Although it is easy to suggest examples of adaptation—a bird’s wing, an eye, a startle reflex—to define one is much more challenging. The status of adaptation always belongs to traits: structures or behaviors, parts of a phenotype. But what sort of trait? An adaptation is a trait that has a particular value or purpose. It is good at something, or good for something. Nowadays natural selection is implicated somehow in expanding upon these sentences. Natural selection explains adaptations, in that natural selection brings adaptations into existence. But little more can be said without entering into controversy.
