This paper begins with the paradox of invariants arising out of random events, and its title is based on the resolution of that paradox in Monod's book Chance and Necessity. In ingestive behavior this paradox arises particularly in the emergence of constancies in intakes from small bouts of behavior. I point out that one resolution of the paradox can be obtained by the use of averaging, eliminating the necessity to search for special detectors of variables whose values appear to be set by small modifications in a variety of control systems. The apparent regulation of body weight or food intake which remains relatively constant in the aggregate while components which enter into them fluctuate widely, is an illustration of the paradox and one possible resolution. I also describe four basic paradigms that could be taken as the main starting points for a comprehensive theory of ingestive behavior. They could be called regulation, learning, reward and neural control. To some extent each is involved, and it is impossible at present to assign primacy. I conclude by suggesting that the basic tenet of ingestive behavior is that it occurs when there is an excess of excitation over inhibition in the neural systems that control it and that the various factors which enter into such a calculation can best be represented by a computer model that incorporates all known controls that will make more accurate predictions than can be made with verbal theorizing. Such predictions can then be used to correct or confirm the model as data is collected. Finally, I provide some specific suggestions for activities of the Society for the Study of Ingestive Behavior. © 1991.
