The function of the brain (and nervous system in general) can be
divided into three essential processes: Identification, Evaluation,
and Selection.
Here is a simple example: A rabbit using its senses would identify
it's situation: "there is a fox running towards me"; it would
experience fear, which is a negative evaluation: "a fox is a
predator of rabbits, so having one running towards me is bad";
and would select a course of action: to run away and hide.
By Identification I mean the entire process of determining what is "out there" in the world. For example, vision is a system for identification. The result of a successful identification is the availability to the brain of a fact about the world.
By Evaluation I mean the process of determining the implication of particular facts for the survival of the organism. For example, pain is system for evaluation -- pain is associated with stimuli (external facts) adverse to survival. The result of a successful evaluation is the availability to the brain of a good/bad judgement. Note that evaluation is relative, in the sense that it pertains specifically to that particular organism's survival, but the correct evaluation is still objective, in the sense that the impact on the animal's survival is a factual matter.
By Selection I mean the process of initiating one among the alternative possible actions the animal could take, based on particular evaluations. For example, locomotion is a process of selection. The result of a successful selection is the maximization of survival, by the attainment of something which is beneficial or the avoidance of something which is detrimental.
I note in passing that each these three process can involve many sub-steps, and on the other hand, two or all of them might be performed by a single neural structure.
For now, I leave it to the reader to convince himself that if the brain could not do any one of these things, it would be useless to be able to do the other two.
copyright 1996 Pam Reinagel
*This page was recovered from the web archive link: https://web.archive.org/web/19970612031146/http://www.klab.caltech.edu/~pam/brain.html