L 



40 J. D. BERNAL 



and metabolism of the nucleated cell. A common pattern underlies all modifica- 

 tions. Not only was life on this Earth one at that level, but also it has not divided 

 into branches ever since. It cannot be just because all hving organisms are part 

 of the food chains of others that they are biochemically compatible. For green 

 plants that do not depend on complex molecules made by other organisms it 

 would be a great biological advantage to be inedible and resistant to fungal 

 and bacterial decay. Yet no plant has achieved this isolation from the rest of the 

 living world. It is precisely because of this biochemical and structural inertia, 

 that we have some reasonable hope of being able to trace back origins by the 

 comparative methods used by Darwin and his followers for gross morphological 

 features in the latter stages of evolution. We may expect patterns of reactions 

 as well as structures to accumulate with modifications and subsequent fusion 

 into more complicated ones and so on until and beyond those found in living 

 things today. The unravelling of protein structure, discussed in my later paper, 

 has shown evidence of several stages of such redupHcations and compUcations or 

 foldings in the most literal sense. Formally the chemical evolutionary process 

 may be likened to the evolution of a drainage for newly emerged lands. Com- 

 paratively trivial variations may determine the location of bends but once the 

 main pattern is cut it deepens and fixes itself only to be changed by the effects of 

 its own actions. A too successful utilization of some component can, as Horowitz 

 [13] has pointed out, lead to the holding up of some activity and the employment 

 of an alternative source. An increase of efficiency in another part may render 

 certain earlier steps urmecessary, but in the main the original pattern will be 

 preserved. We should, as time goes on, be able to trace it even more accurately. 



We may define life, for the sake of this discussion only, as the embodiment 

 within a certain volume of self -maintaining chemical processes. Our central problem 

 is not here to explain how such a system works but how it can establish itself 

 starting from available inorganic materials and subsequently reproduce and 

 evolve de novo. This can be divided into four inter-related but distinct problems : 



(i) the problem of the external source of free energy to keep the system going; 



(2) the problem of the facilitation of the energy interchanges within the system, 

 where an isothermal condition implies some catalysis ; 



(3) the problems of the means of holding the system together and in the more 

 complicated cases, such as bacterial and nucleated cells, of how all parts of the 

 organism can maintain their individuality while being in constant chemical 

 relation with each other; 



(4) the problems of reproduction with its almost, but never quite exact, 

 duplication of organisms as shown in evolving species, pose the further problem 

 of the normal transference, with occasional modification, of specific guiding 

 patterns. 



All these problems are being discussed in various sections of this Symposium. 

 I list them here simply to provide a general background for a tentative establish- 

 ment of stages in biopoesis. Although they overlap, the four conditions for life 

 listed above form a natural order. The energy source must come first, there must 

 be some reactions or mere coherence would not imply life and there can be no 

 reproduction without something to reproduce. An analysis of biopoesis can be 



