78 N. W. PIRIE 



chemical reasons [5] for thinking that the probiotic atmosphere was mainly 

 CO2 and N2. 



As knowledge grows the range of possible compositions for Earth's surface 

 will be narrowed. It could be argued that discussions about biopoesis might well 

 wait till this narrowing had taken place. There are two important reasons for 

 disagreeing with this idea. The urge to solve the problem of the origin of life 

 is an important stimulus for the accumulation of evidence about the original 

 environment. Reciprocally, if biochemical research could define unequivocally 

 the necessary qualities and composition of an original organism, or eobiont*, 

 this would define the conditions in at least part of the primitive environment. 

 It would be analogous to the use of the morphology of fossils to define whether 

 the region in which they hved was dry land, marsh or water. 



There are many difficulties here. I have already argued [7] that, even with 

 existing organisms and systems a rigid division into the living and the non- 

 living is not possible. Every criterion that has been suggested will both exclude 

 something that, for aesthetic reasons, we wish to call hving and include some- 

 thing that we do not. Something more satisfactory could be achieved by saying 

 that a living organism had to show some arbitrary number out of a group of 

 quahties but in practice this would be almost as clumsy as a catalogue of the 

 things we intend to call hving and it would operate particularly badly among 

 the simpler systems where the issue becomes of most interest. It seems better to 

 recognize that life is not a definable quahty but a statement of our attitude of 

 mind towards a system. This makes Ufe a faUible guide through geochemistry. 



Even if it is not possible to say that a system with certain activities is alive 

 it may yet be possible to say that certain chemical substances or processes are 

 pecuhar to hfe and essential for it. A cursory study of present-day organisms 

 shows many uniformities in their use of proteins, fats, carbohydrates, phosphoric 

 esters etc. At one time particular attention was attached to the proteins, now there 

 is a tendency to use the phosphoric esters as the fundamental criterion of life. 

 It is of course perfectly legitimate to say that you do not propose to call any system 

 aUve unless it contains protein. That estabhshes a simple hnguistic rule and it is 

 essentially what Engels did in his celebrated dictum. But it is not a very useful 

 point to make because not all systems containing protein or phosphoric esters 

 are aUve and to say that whatever else a system may be doing, it cannot be called 

 ahve if it does not contain the chosen substance, seems to be as arbitrary as the 

 erection of a colour bar among people. 



All present-day forms of life that have been examined contain protein. The 

 number examined is only a small proportion of the whole but protein-based 

 mechanisms seem to be so efficient that it is Hkely that most or even all the other 

 forms of hfe also use proteins now. If this turns out to be so it will have no more 

 relevance for a discussion about the origins of life than the now almost universal 

 use of paper has for the origin of writing or the use of matches for the original 

 making of fire. The first metal frying pan was probably made of gold because 

 that metal was available and usable though later ousted. The point is worth 



* I have proposed elsewhere [6] the words biopoesis and eobiont for the origination of 

 life and for the first organisms originated and argued the advantages of the new words. 



