Four Questions, One Behavior
Niko Tinbergen argued that a complete biological explanation of any behavior requires answering four questions, split into two distinct levels.
Proximate causes explain how a behavior happens right now: Mechanism covers its neural, hormonal, or physiological basis, while Ontogeny covers how the behavior develops across an individual's lifetime.
Ultimate causes explain why the behavior exists in the long run: Function is the survival or reproductive advantage it provides, and Phylogeny traces its evolutionary history across related species. Missing any single question leaves the biological story incomplete.
Complementary Levels
| Level | Question | Bird Song Example |
|---|---|---|
| Proximate | Mechanism | Syrinx and seasonal hormones drive physical singing |
| Proximate | Ontogeny | Young birds learn songs from adult tutors |
| Ultimate | Function | Singing attracts mates and defends territory |
| Ultimate | Phylogeny | Song evolves from ancestral vocalizations |
Common pitfall: Treating a Mechanism ("how") as a rival to a Function ("why"). Hormonal causes and evolutionary functions are complementary perspectives on the exact same behavior, never substitutes.