Every complex behavior challenges us to identify its origins. How do birds know to migrate south for the winter? How do border collies know to herd sheep? How do sea turtles find their way back home to the beach on which they hatched? As a shorthand—as an aid to communication—we might talk about a migratory instinct, a herding instinct, or a homing instinct. Such labels may seem gratifying, but it is an illusory gratification. Scratch the surface of any complex, adaptive behavior and one is confronted with a seemingly endless array of hard questions spanning evolutionary and developmental time, the intricacies of ecological and social experience, and the machinations of the nervous system with its billions of neurons. The more we dive into these matters, the harder it is to settle on any clear notion of what an instinct actually is. As Patrick Bateson1 has pointed out, this conceptual confusion about instinct is reflected in the many meanings that are routinely ascribed to it, including:
- present at birth,
- not learned
- developed before it is used
- unchanged once developed
- shared by all members of a species
- adapted during evolution
- served by a distinct module in the brain
- attributable to genes
Scientists often unknowingly invoke more than one of these meanings at any given time, and may even unwittingly switch between meanings in a single article. This isn't just a matter of lazy thinking. The murkiness of the term reflects actual confusion about the subject. No one doubts the existence of species-typical behaviors, and we can all agree that any science of behavior must endeavor to make sense of them. But there is an unsettling gulf between widely accepted assumptions surrounding instinct and the actual science available to explain it.
