xxxii. 18 EVOLUTIONARY PROGRESS 785 



only a development of the general tendency to self-maintenance, which 

 characterizes all living organisms; but it is carried to its extreme in the 

 higher vertebrates, giving them the power to maintain life under varied 

 and unpropitious conditions. 



18. The influences controlling evolutionary progress 



Our analysis of the factors affecting evolution gives us clues about 

 the influences that have produced this increase of complexity. Excess 

 productivity and intra-specific competition force sections of the popu- 

 lation to try new habits. Those with the ability to do so may, if they 

 can tolerate new external conditions, find situations in which they can 

 flourish. So a new type becomes developed, only to meet later the 

 competition of its own descendants or other invaders and hence be 

 driven to extinction or to the colonization of still other fields. 



If we have interpreted the situation correctly there can be said to 

 be an evolutionary path that is progressive, in the sense of enabling 

 life to be lived effectively under wider and wider conditions. Lotka 

 has suggested that it is possible to recognize a 'basic principle defining 

 the direction of organic evolution', namely, that the collective effects 

 of organisms 'tend to maximize, on the one hand, the energy intake 

 of organic nature from the sun, and on the other, the outgo of free 

 energy by dissipative processes in living and in decaying dead organ- 

 isms'. This increasing turn-over of energy is presumably a sign of the 

 development of more and more complicated mechanisms for ensuring 

 homeostasis in spite of external changes. These mechanisms in turn 

 depend upon an increasing store of instructions in the genotype. If this 

 view is correct there is a tendency for organisms to come to represent 

 more and more features of the environment, which is another way of 

 saying that they have more information about it. More simply still we 

 may say that they come to be able to live under ever more 'difficult' 

 conditions, gathering and expending more energy in order to keep 

 alive (Young, 1938). It seems reasonable that this increase of complexity 

 should be progressive; as the organisms acquire more information 

 about the environment they also gain in possibility of acquiring still 

 more. In particular those that develop mechanisms for learning directly 

 with the nervous system will be successful and will evolve fast. It is 

 possible in this way to see the basis for the direction of evolutionary 

 change. Such a formulation is far from exact, however, and the process 

 clearly depends upon many conditions not here specified, for example 

 as to the nature of environmental changes and the effects of interaction 

 between organisms. 



