Wing color in Heliconius butterflies is an example of frequency-dependent selection.

Within the Heliconius group of butterflies found in central and south America, there are several morphs within a species, each morph having a different color pattern. All the morphs are poisonous. When a morph is common, it will be more likely that birds will have already learned to avoid them, whereas birds will not yet have learned to avoid a rare morph. An individual of a rare morph is therefore more likely to be the unlucky prey that educates the bird, and gets killed in the process. The fitness of each morph is positively frequency-dependent.

The image opposite is of a variety of morphs of the Heliconius erato species.