Evolution.

Society for Experimental Biology

Date:: 1953

Catalogue details

Licence: Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)

Credit: Evolution. Source: Wellcome Collection.

29/484 (page 5)

THE ORIGIN OF LIFE 5 collected into a coherent system and showing the djoiamic stability with overall growth which is one of the essential features of life. These two authors make a noble attempt to narrow the gap from the inorganic to the biochemical worlds, but neither of them treats in any detail of the pro¬ gressive nature of the process of evolution or suggests how each stage became fixed and self-perpetuating in a world in which, presumably, the same entropy-increasing tendencies were as powerful as they are to-day. Bemal avoids the difficult task of defining what is meant by the beginning of life, but he implies that life had a beginning. The earlier biologists rejected this idea, maintaining that the individual characteristics of life are eternal, in the sense that they have always been present in some properties of the universe, and that only in the coming together of these properties into a coherent and persistent system, small on the cosmic scale, do the properties of living organisms as we know them represent any change in the dynamic characteristics of the natural world. The hierarchy of open systems (Bertalanffy, 1952)—the complex of dynamic systems within dynamic systems—constitutes the essential novelty, not the individual dynamic systems themselves, of which a wide variety can be found in nature similar in their kinetic behaviour to those occurring in living organisms. At this stage in the argument it may be useful to restate more precisely those characteristics of evolution for which this universal and perpetual claim is made, and to relate them to the other law which gives direction to the arrow of time, the Second Law of Thermodynamics and the Equi- partition Principle from which this law derives. The second law applies to chemical and physical systems which are isolated in the sense that energy does not cross the boundary of the system, and states that in such systems entropy always tends to increase, or that the state of the system becomes progressively more 'random'. A feature of the evolution of living organisms and of many processes taking place within living organisms is that in them entropy appears to decrease at the expense of a greater entropy increase in the environment. This point was clearly put by Schroedinger (1948), and the fact that living systems are not isolated—that energy does cross the boundaries of the system—makes this state of affairs consistent with the second law. In more detailed analysis, the aspect of the behaviour of living systems which makes possible this localized entropy decrease is the auto- catalytic synthesis of material substance comprised in the living system. The use of the term ' autocatalytic ' in this context is liable to be mis¬ leading, but there is no other word which carries the same implications. It does not, of course, imply, in the sense in which the term is often used in physical chemistry, that the rate of increase of a particular substance is