Chemical Diversity and the Origins of Life 



N. W. PIRIE 

 Rothamsted Experimental Station, Harpenden, Great Britain 



Contemporary discussions about the origin of life start with the simplifying 

 assumption that no occult phenomena are involved and no forces or principles 

 operated to bring Hfe into being in the past that do not operate now. This as- 

 sumption is sometimes called the 'uniformitarian' principle. The chemistry and 

 physics with which biology is and has been concerned is the ordinary chemistry and 

 physics of the period at issue but we know very httle even of the chemistry 

 and physics of to-day and the litde we know is not necessarily the most relevant 

 part. Furthermore, Haldane argues [i, 2] that chemistry and physics may have 

 been significandy different in the Pre-Cambrian. That would complicate detailed 

 interpretation but would not affect the principle. 



This basic assumption has been made by most scientists and philosophers 

 who have considered the problem. They have not disagreed about whether life 

 could originate from non-Hving matter but only about how often it did so. The 

 2500 year history of this dispute has often been surveyed (e.g. Huxley, Tyndall, 

 Oparin). On the one side we have such men as Redi, Spallanzani, Pasteur and 

 Tyndall who regarded the event as so infrequent that it could be disregarded 

 in the course of ordinary work; on the other such men as van Helmont, Needham, 

 Pouchet and Bastian who looked on it as an easy and regular transition. Although 

 the dispute did not always proceed along strictly objective hues it was extremely 

 valuable both in integrating knowledge and in uncovering new phenomena. In 

 this respect it contrasts with the idea that 'Life' is something quite different from 

 anything else and that it either comes to us from space or is the consequence of 

 special activity by a deity or demiurge. Though sterile, this conclusion has been 

 common among physicists and engineers and has been come to by a few biologists 

 such as Linnaeus and Wallace. 



The 'uniformitarian' principle takes us to the limit of simphcity. Before we 

 can frame a theory of the origin of life we should know the nature of the environ- 

 ment in which it originated and we should know, or be able to define, the criteria 

 by which we would define or recognize it. Unfortimately we know neither. 

 During the nineteenth century it was generally assumed that Earth had cooled 

 from an incandescent mass so that if any form of life had been carried over from 

 an earlier phase in its history it must have been carried by silicates or some 

 such thermostable material. The discovery of radioactivity made the idea tenable 

 that Earth originated by the accretion of cold interstellar detritus and so made 

 the old 'cosmozoic' idea a little more attractive. But this idea merely moves our 

 problem to a different environment [3] and does nothing to solve it. At present 

 there are advocates for both a hot and a cold origin of Earth so that it would 

 seem wise not to make our theory of the origin of life depend exclusively on either. 



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