Information Theory in Biology
Control Systems Laboratory, U. Illinois, 1952One of the basic tools in natural science is the energy concept. In recent years, another concept has begun to attain comparable dignity. It is something more subtle and elusive than energy; it is derived from a desire for dealing methodically with problems of complexity, order, organization, specificity.... It is known as entropy or amount of information, and plays a prominent role in the new fields of information theory, communication theory, and cybernetics. The "new movement" is based on evaluative concepts (R. A. Fisher,' s experimental design, A. Wald's statistical decision function, J. von Neumann's theory of games), on the development of a measure of information (R. Hartley, D. Gabor, N. Wiener, C. Shannon), on studies of control mechanisms, and the analysis and design of large systems (W. S. McCulloch and W. Pitt's "neurons," J. von Neumann's theory of complicated automata, N. Wiener's cybernetics). It has become increasingly evident that the principles of information theory are applicable to the "higher" functions of living organisms. They can also be used to advantage in analyzing basic functions such as metabolism, growth, and differentiation. There are remarks to that effect in Wiener's Cybernetics; in E. Schrödinger's What is Life? there is a provocative discussion on how organisms feed on negative entropy." In the present volume, the formalism of information theory and cybernetics has been applied to some basic biological problems, with some degree of success. The amount of control and communication involved in the basic biological processes is very great. Indeed, it appears that there is little difference between the exercise of the basic biological activities, and the exercise of the most sophisticated skills in the most highly differentiated organisms. We do not claim that the absolute difference between basic and highly specialized activities is small; after all, this difference is the result of the order of a billion years of organic evolution. The claim is only that the gap between simple and complicated living organisms is small in comparison to the gap which separates the simplest living things from the most complicated non-living systems, say, between a bacterium and a giant electronic brain. Thus, when we say that the functional complexities of man and bacterium are closely comparable, we do so, not because of a low estimate of the functional complexity of man, but because we are very much impressed by the complexity of bacterial life. The cybernetics of biological functions should ultimately contribute to the understanding of the nature of biological control systems. The first stage in the analysis is quantification: a count of control elements, a measure of the amount of control exercised. Most papers in this volume deal with counts and measures; only on a few occasions have steps beyond this stage been attempted. It is in the nature of cybernetics that it cuts across traditional boundaries between various fields of science. Because of this, symposia have played a major part in its development--in particular, the British symposia ('50, 52), the series of Macy conferences,- the French symposium ('52). The present volume, too, is the result of a cooperative effort; it stems largely from lectures and discussions arranged, in the summer of 1952, under the auspices of the Control Systems Laboratory at the University of Illinois.