Chemical Diversity and the Origins of Life 61 



to think that they were all present, that they were present in all forms, or that 

 when present they were quantitatively important. Life now is the result of two 

 quite independent processes; the random appearance of capacities in small 

 atypical regions, and the integration of these capacities into a mechanism adapted 

 to survival in the enviroimient that exists more generally. The former may 

 have been concerned predominantly with reactions that are now unusual but 

 they are the processes that should be taken as the origins of hfe. This point of 

 view is roughly illustrated in the diagram (Fig. i). Two cones are set apex to 

 apex and the number of processes used by all the forms of hfe at any time is 

 indicated by the width of the cone at that time. The broad base thus shows the 

 original biochemical complexity, the broad top the present morphological 

 complexity, and the narrow middle is the conventional 'origin of hfe'. 



At each stage of science there has been a tendency to associate life with a 

 recently discovered type of phenomenon. At one time it was magnetism. Then 

 Pasteur overstressed the relevance of optical activity* and pointed out the 

 analogy with crystaUization. Proteins and adenosine triphosphate have had 

 their turn and now there is a tendency to overstress isotopic fractionation. Living 

 systems, hke all other systems with a series of stages of adsorption, diffusion, or 

 phase equihbrium, may differentiate between isotopes. They pack the regions 

 of separation into smaller compass than an isotope separation factory but they 

 only perform the same fractionation that a long enough column of suitable 

 mineral adsorbent would. An unusually high ratio of i^C to i^C in a structure 

 is prima facie evidence that C was once part of an organism, but other systems 

 can fractionate C isotopes and living systems do not at all times fractionate 

 them in the same way [14]. The Universe contains a vast range of processes and 

 types of compound. It is probable that none of these appear exclusively in Uving 

 systems but it is equally probable that many more have appeared or still appear 

 in them than is generally assumed. 



The argument has been presented here in terms of the elements because they 

 make it easy to put diversity on to a quantitative basis. Somewhat similar con- 

 clusions can be drawn from other aspects of chemistry. The more primitive 

 animal species have the most complex fats [15], this may be a consequence of 

 their failure to fractionate food fats [16, 17] but that in itself is evidence of 

 versatiHty. Some insects use substances such as formic acid and the oxides of 

 nitrogen that seem to fall outside the range of normal biochemistry and they 

 may well have been doing this for 100,000,000 years. The simpler organisms 

 such as moulds and bacteria handle a more diverse group of metaboUtes and 

 make a more diverse group of excretory products than any other organisms but 

 there is no evidence about the antiquity of the species. In summary: the develop- 

 ment of morphological complexity has been associated with some biochemical 

 simplification, in the process many originally vital activities have probably been 

 lost and the relative importance of others has probably altered. This Symposiimi 

 will have demonstrated that there is no basis for dogmatism about the processes 

 involved in the origins of life; my contention is that there is not yet even a basis 



* This point has been elaborated elsewhere (N. W. Pirie, Trans. Bose Res. Inst., 22 j 

 III, 1958). 



