Introduction

Abstract

Table 1.1 gives approximate numbers of a few of the components of the human nervous system. These numbers alone are impressively large, but the true complexity of the nervous system must also take into account the interactions among these components. If we attempt to understand the function of the nervous system in a reductionist way by identifying the function and interaction of each component as the basis upon which to build an understanding of the whole, we will have little hope of success. On the other hand, we can accept the premise that evolution designs conservatively so that functions tend to be reused to solve similar problems. This gives us an incentive to seek and to understand prototypical operators that occur in multiple locations and species. We can concentrate, then, on similarity of function without having to catalogue each occurrence separately.