Four Questions, One Behavior
Niko Tinbergen proposed that a complete biological explanation of any behavior must answer four questions, grouped into two levels. Proximate causes explain how a behavior happens right now: Mechanism is its physiological, neural, or hormonal basis, and Ontogeny is how the behavior develops across an individual's lifetime. Ultimate causes explain why the behavior exists at all: Function is the survival or reproductive advantage it provides, and Phylogeny is its evolutionary history across related species.
Applied to bird song: the mechanism involves the syrinx and seasonal hormone changes; the ontogeny involves a young bird learning its song from adult tutors; the function is attracting mates and defending territory; and the phylogeny traces how song evolved from ancestral vocalizations. Missing any one question leaves an incomplete story.
| Level | Question | Example (bird song) |
|---|---|---|
| Proximate | Mechanism | Syrinx and hormones drive the physical act of singing |
| Proximate | Ontogeny | The song is learned from adult tutors during development |
| Ultimate | Function | Singing attracts mates and defends territory |
| Ultimate | Phylogeny | Song traces an evolutionary lineage across bird species |
A common error is treating one of the four as the "real" explanation and the others as optional detail. In fact they are complementary: a hormonal mechanism and a territorial function are both true simultaneously, at different levels of analysis, and neither one substitutes for the other.
Common pitfall: treating a "how" answer (mechanism) as though it competes with a "why" answer (function). Asking how a bird's syrinx produces song and asking why singing evolved are both legitimate questions about the very same behavior — not rival explanations.