A framework for the study of behavior

• New formulation of Tinbergen's questions.
• Extended description of behavior systems.
• Relation of cause and function.

Behavior is defined as the expression of the activity of the nervous system. The basic units of behavior are perceptual mechanisms, central mechanisms, and motor mechanisms. These units can be organized into more complex units called behavior systems such as hunger, sex, aggression, fear, etc. Perceptual and central mechanisms include cognitive mechanisms such as ideas, beliefs, memories, intentions, and cognitive modules. Behavior can be analyzed at genetic, physiological, whole organism, and population levels, and the concepts used to analyze behavior should be appropriate to each level. One can ask causal, structural, and functional questions about current behavior, ontogeny, and phylogeny. Causal and functional questions are independent of each other and should not be confused. There has been much confusion and disagreement about the relation between cause and function, and several examples are analyzed.This article is part of a Special Issue entitled: In Honor of Jerry Hogan.