CHAPTER IX 



THE FURTHER EVOLUTION OF 

 THE FIRST ORGANISMS 



The concept of comparative 

 biochemistry. 



Strictly speaking, the origin of the first organisms should 

 conclude an exposition of the origin of life on the Earth. 

 When this had taken place matter entered into a new, bio- 

 logical stage of its development. There began the evolution 

 of living things from the most primitive original organisms 

 to the highly-developed plants and animals which now live 

 on our planet. 



Careful study of this already purely biological evolution 

 may, however, be very helpful towards understanding the 

 actual origin of life, the way in which it came into being. 

 At the present time we cannot observe this process directly 

 in nature because all the intermediate links, the more primi- 

 tive and incomplete forms of organisation of living matter, 

 would appear to have been destroyed long ago, swept from 

 the face of the Earth by natural selection. However, a study 

 of the organisation of protoplasm in contemporary organisms 

 at different levels on the evolutionary scale provides us with 

 some objective evidence as to the nature of the earliest forms 

 in which life existed on the Earth. 



Especially valuable in this respect is the study of metabol- 

 ism, that ordered series of biochemical processes which forms 

 the basis of the organisation of protoplasm in time and in 

 space. As we saw above, metabolism occurred even in the 

 very earliest organisms, but was altered and brought to a 

 higher degree of integration dining the process of their 

 evolutionary development. This involved the repeated appear- 

 ance of new conjunctions of biochemical reactions and new 

 chemical mechanisms within the protoplasm on which these 

 reactions depended. These enabled organisms to make better 



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