If we may rely for our evidence on simple observation, it would appear that the tendency of random or unguided activity in external nature is opposed to the development of complex organization and favorable to structural simplicity—in the sense of uniformity in the distribution of elements. This anti-organizing trend of purely physical processes is illustrated in ordinary large-scale mixing and stirring operations, as well as in the automatic increase of entropy with time in systems subject to the laws of thermodynamics (material or molecular systems in general). It is common experience that complex systems which are the seat of physical activity tend to become simpler when left to themselves, i.e., they lose organization. Recently Eddington has given the whole matter an admirably clear expression: “Entropy may most conveniently be described as the measure of disorganization of a system. ... We can see chance creeping in where formerly it was excluded.” Unless counteracted by directive action the casual or random element in nature tends to increase. If things are left to chance, not only does organization of any high degree of complexity fail to develop, but what organization there is tends to lapse or disappear. Hence in those cases, such as living organisms, where the existence and activity of the system depend on a special and complex organization, it appears necessary to assume the continued operation of a stable directive influence or factor which pervades the whole system and excludes or compensates casual factors as far as possible. The presence of this factor is what makes possible the development and maintenance of the organization required for vital activity.