The Biological Causes of Irrationality

Abstract

Everyone is irrational in one way or another, as I have tried to show in a recent book (Sutherland 1992), which lists about 100 different kinds of irrational behav- iour. Only a few can be mentioned here. For full documentation of the phenomena described below, the reader should refer to my book, which cites the relevant experiments. I am indebted to others for the experimental findings, but the specu- lations on the biological origins of irrationality are my own. It is important to be clear what constitutes irrationality; one must start by defining rationality. A rational decision is one that is most likely to lead to the end in view, given the knowledge that is available. An irrational decision is one that departs from this definition. Even rational decisions may not achieve their ends. If someone offers to bet you a pound to a penny that a toss of a coin will come down heads, it is rational to accept the bet, but you may lose money instead of gaining it. The uncertainty of human life means that almost all decisions are based on the balance of probabilities.