Proximate and ultimate factors

Richard Brewer

When we ask a biological question with a ‘why’ in it – “Why do birds migrate?” or “Why do varying hares turn white in the winter?” – we are usually asking two separate questions with quite different answers. We are asking, on the one hand, what it is in the environment of the organism that make it migrate or turn white. That is, what features of the environment serve as cues for the organism to respond physiologically of behaviorally in this way? We are asking, secondly, an evolutionary question: what makes it advantageous or necessary for the organism to migrate or turn white? The answers to the first question are proximate factors, and to the second, ultimate factors. This terminology was first employed by the British biologist J. R. Baker in writing about a questiono of the same sort, “Why do birds breed when they do?”

Fonte: Brewer, R. 1979. Principles of ecology. Philadelphia, Saunders.