8 I The Process of Evolution 



teinoids). Proteinoids in water tend to form spherules of varying 

 size and shape, depending upon their interaction with substances 

 mixed with them. These spherules, in some respects, resemble co- 

 acervates and other cell models. Among other things, the proteinoid 

 spherules retain their integrity for rather long periods and are not 

 destroyed by high-speed centrifugation. 



ORIGIN OF SELF-REPLICATING 

 SYSTEMS 



Thus it can be seen that there were diverse ways in which organic 

 compounds may have been produced on the primitive earth. It is 

 not unreasonable to assume, therefore, that the primitive ocean was 

 comparable to a thin soup of organic materials. There is little agree- 

 ment as to how the first self-replicating systems developed in this 

 "soup. " Obviously, what was first required was the selective con- 

 struction of molecules. Calvin has pointed out that the phenomenon 

 of autocatalysis has the nature of a selective process. Autocatalysis 

 occurs whenever the product of a chemical reaction has the property 

 of influencing catalytically the rate of its own formation. There 

 follows a progressive build-up of products in a sequence of in- 

 creasingly complex compounds formed from simpler ones. An early 

 selection of this nature (for complexity) must have gone on in the 

 organic soup. 



Autocatalytic reactions are only partly analogous to a self-replicat- 

 ing living system. No presently known substance, when isolated, will 

 replicate itself. Only systems have the ability to replicate. The living 

 systems familiar to us are composed of proteins and nucleic acids, 

 together with some means of energy mobilization. Polypeptide 

 chains, the backbones of protein molecules, are formed by the link- 

 age of amino acids in linear series. The linkage is accompanied by 

 the elimination of water as the amino acid chain lengthens. The 

 bonds between the amino acid units are known as peptide bonds. 

 The spontaneous formation of even a small protein in a solution of 

 amino acids requires outside energy and is a very improbable event. 

 But in the absence of free oxygen and predatory organisms, the life 

 of an amino acid "soup" could be extremely long, long enough to 

 turn the improbable into the probable. ( The chance of being struck 

 by lightning in a 70-year life span is very slight, but if one lives for 

 700 million years it becomes almost a certainty. ) 



However, as Wald points out, the spontaneous generation of 

 protein molecules is opposed by their tendency toward spontaneous 

 dissolution. Indeed, the equilibrium point in the reversible, spon- 



