Introduction 



When, during the nineteenth century, men of science discussed the origin of 

 life, as they have done extensively, they were concerned with the supposed 

 formation of infusoria and other micro-organisms from particles of organic 

 matter. In the frame of the current philosophy of the age, it v^as common creed 

 to accept the occurrence of such an event, as, in the current philosophy of the 

 sixteenth century, it appeared obvious that the animal spirits of a dirty shirt 

 could produce a litter of mice. It appeared as such due to the fact that the 

 complexities of the embryogeny of a mouse were still imknown. This was no 

 longer the case during the nineteenth century when such notions were con- 

 sidered as being pure fallacy. As their extreme biochemical complexities were 

 still unknown, nothing prevented believing that simple micro-organisms such 

 as bacteria could not be formed by the simple aggregation of particles or 

 organic matter, and furthermore, this was proved by experiments. Bad experi- 

 ments, as was shown by Theodor Schwann and by Louis Pasteur. Life on our 

 earth is made of cells, modified cells of products of cell activity. Cell structure, 

 biochemistry and physiology are today the focus of attention of biologists and 

 the main subject of their research. We have learned that cells differentiate in 

 the course of the development of a multicellular organism. We recognize, by the 

 comparative study of cells and of organisms, that there are primitive aspects 

 and more differentiated aspects of cell structure and of cell chemistry. Com- 

 parative biochemistry brings to light a number of evolutionary aspects of the 

 biochemistry of cells and organisms. This knowledge leads us to beheve that if 

 we could follow the course of time backwards, we would find primitive cells, 

 and before them, some kinds of cell precursors. As we know that the continuity 

 of life and the transmission of characters, as well as the possibility for these 

 characters to change, is insured by a code of hereditary transmission of a 

 chemical message, we are inclined to believe that this code, represented by 

 macromolecules of nucleic acids, is a very ancient feature of life. But to imagine 

 in what form of cell or precellular structure it first appeared, or even if it has 

 first appeared in the free stage, belongs to the realm of mere speculation. 



To stay on firmer ground, we can start from the other end of the chain of 

 events, i.e. go from molecules to primitive cells. Until Oparin pubHshed his 

 epoch-making booklet in 1923, it was a common belief that organic substances 

 were the products of hving organisms. With the notion of a panglobal soup made 

 of a solution of organic and inorganic substances, the problem of the origin of 

 life brought a new and powerful appeal to biological thought and experimenta- 

 tion. Whether a large number of metabohc systems and the corresponding 

 enzymes became widely distributed in a metabolizing soup, or if these inventions 

 took place locally in discrete organisms, remain a field for speculation. With 

 more probable data on the situation reigning on the primitive earth, it again 



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