Some Systems Theoretical Problems in Biology

Abstract

Biology begins with the recognition of what we call living organisms as a separate class of entities, distinguished in structure and properties from the rest of the natural world. The intuitions on which this recognition is based are a mixture of introspections and experience, which despite great effort have never been completely formalized; that is, no one has ever been able to put forward a finite set of structural propositions that are satisfied by exactly those physical systems which our intuition tells us are organisms. Nevertheless, most of us take our intuitions on this matter seriously enough to believe that we can make a useful, scientifically significant distinction between living and nonliving, organic and inorganic. The absence of formalization means, however, that we cannot sharply specify the boundaries which separate the living from the nonliving. We encounter such boundaries when we ask, as some people do, whether viruses are alive, or whether it is possible to construct machines which can “live” in some sense, or whether there are other kinds of physicochemical systems (e.g., on the planet Jupiter) which we would want to classify as “living systems.”