PREFACE vii 



lation of neutrality (the concentration of ion- 

 ized hydrogen and hydroxyl at the neutral 

 point). 



One does not like to accept a fact of such 

 far-reaching importance as mere chance, and 

 yet no other explanation was at hand. For, 

 after the briefest consideration, it was obvious 

 that here, at least, natural selection could not 

 be involved. But it was also certain t hat th is 

 is no unique instance of a property of a simple 

 substance automatically serving a very u sefu l 

 purpose in the processes of life. Like every 



one who has received a chemical^ training, I 

 was vaguely conscious of numerous other simi- 

 lar cases ; like every one_who has any acquaint- 

 ance with the general properties of m atterTT 

 knew that the remarkable thermal properties, 

 of water are of great importance to living or- 

 ganisms. However, in spite of the fact that 

 I had been brought face to face with a definite 

 problem whose solution now appears to be 

 perfectly patent, so great is the natural inertia 

 of the mind, and so firmly established was the 

 belief th at naturalsele ction is, on the wKbTe, 

 quite adequate to account" for biological fit- 

 ness, that for a number of years I made no 

 further progress. 



Then, finally, after a long period of uncer- 

 tainty, came the realization of the reciprocal 



