The proximate and the ultimate: past, present, and future.

The distinctions inherent in the proximate-ultimate dichotomy have a long history. I examined several issues related to this distinction. It is important that distinctions among different problem areas be made so that the type of answer presented in research in animal behavior is appropriate for the type of questions being asked. This may require more than the two-way distinction between the proximate and the ultimate. I suggest that such terms as 'function', 'ultimate', and 'ultimate causation' be re-evaluated. Methodological problems encountered when measuring differential adaptive consequences of alternative behavioral patterns and when using proximate stimulus control to infer adaptive significance require further consideration.