EVOLUTION IN GENERAL 275 



and most reasonable assumption to make that all these primitive 

 organisms were of the same kind and were distributed with the 

 same degree of uniformity as the materials of the lithosphere. 



Organic evolution proceeds and we know enough of its history 

 to convince us that its tendency is for simple organisms to become 

 more complex and for an initial phase of uniform distribution to 

 become replaced by later phases in which the distribution became 

 much less uniform. If we divide up the surface of the earth into 

 regions and sample these at random we shall certainly find that 

 it is very improbable that any two regions taken at random will 

 contain the same kinds of organisms. Therefore a distribution 

 of the elements of a system that was initially probable has become 

 very improbable because of its evolution. 



Next we may take a developmental process, say that of a plant 

 seed. The organism, or seed, is at first simple in structure but, 

 as its development proceeds, it becomes more complex. It is a 

 very small body, say an acorn, but it becomes a great tree. The 

 substances of this body (water, CO 2 and simple mineral salts) 

 were originally chemical molecules that were simple in configura- 

 tion and were widely diffused throughout the lithosphere, hydro- 

 sphere and atmosphere, but as the development proceeds they 

 become more and more concentrated, in the body of the tree, 

 as chemical molecules that are complex in configuration. The 

 energy that became embodied, in the potential mode, in these 

 complex molecules was initially widely diffused in space as solar 

 radiation. Thus configurations and distributions that were 

 probable ones have become much less probable in the course 

 of organic development and growth. 



These examples will show what is the tendency of all organic 

 evolutionary processes — the analyses of other particular examples 

 of such process lead to essentially the same result. There is 

 always some aspect of an organic evolution which shows that 

 distributions and configurations of the organic syste?n considered 

 become less and less probable as the evolution continues. And with 

 this decreasing probability the entropy of the system also decreases. 



The entropy may be regarded as a function that describes the 

 interchanges of energy between the evolving system and all the 

 other things in its environment. The entropy of the universe, 

 as a whole, continually tends towards some future maximal value 

 and this means that energy that is available for transformations 



