EVOLUTION 17 



be looked for from the co-operation of the chemist and 

 physicist. 



From the evolutionary standpoint may not a chemical 

 compomid be regarded as the analogue of a biological 

 ' species ' ? The chemist may be looked upon as a select- 

 ing agent acting in the present state of knowledge as 

 a more or less unconscious agent. He is as dependent for 

 his ' species ' upon intra-molecular dynamical conditions 

 as is natural or artificial selection upon the congenital 

 variations offered by the Hving organism. Moreover, the 

 compounds which he isolates are adaptations to a par- 

 ticular environment — they consist of molecules capable 

 of existence only under the particular environmental 

 conditions imposed. Change the conditions, such for 

 example as by raising the temperature, and a different 

 order of chemical combination becomes possible. Out of 

 various possible combinations of particular atoms in 

 particular ways the chemist therefore can only produce 

 such compounds as are capable of survival under his 

 laboratory conditions. The * fittest ' that here survives 

 is the product of chemical skill only in the same sense 

 that a race is the product of artificial selection, or a species 

 the product of natural selection. Darwin's prime con- 

 ditions of organic evolution — ^the nature of the organism 

 and the nature of the environment — are complied with 

 if for ' organism ' we substitute ' atomic configuration ', 

 and if by ' environment ' we mean physical and chemical 

 environment. The analogy between a chemical compound 

 and a species is also borne out by the circumstance that 

 in reaching the final stage intermediate unstable stages 

 are frequently if not generally passed through — ^the 

 • unfit ' with respect to the final environmental conditions. 

 Furthermore, in some cases the internal mechanism is so 

 evenly balanced that the final product may be said to 

 possess a power of responsivity, being capable of existing 

 in one or another of certain distinct modifications accord- 

 ing to its chemical or physical environment. This is what 

 chemists know as * tautomerism ', ' dynamical isomerism ', 



c 



