Sumtnarv and General Discussion 363 



later it continues primarily by an environmental social, Lamarckian 

 kind. I shall return to this shortly, but must first examine the 

 last major topic, the fixation of information. 



For experience to be fixed or information to be stored, there 

 must be a material change of some kind. If a system is to retain 

 an enduring difference induced by the environment, not just a 

 relatively ephemeral change in dynamic state, as a spinning top, 

 the different responsiveness must rest on a morphological differ- 

 ence. Such a material change can be only in the number or kind 

 or position of units, suc'i as ions, molecules, organelles, cells, or 

 perhaps all of these. One is tempted to look at the macromolecules 

 because, at least at that level, they are the only units that have 

 considerable endurance in cells. It is by no means excluded that 

 the lipids, which endure very well (some of them, once formed, 

 apparently have no turnov^er during the life of the brain), or the 

 proteins might be involved; but most investigators interested 

 in this field have a strong predilection for the polynucleotides. 

 Moreover, as pointed out earlier in this symposium, there is 

 growing evidence that implicates them, and there is an especially 

 intriguing reason for interest in RNA and memory. 



DNA molecules produce another generation of DNA, these 

 produce another generation, and so on. For a series of generations, 

 the important thing, of course, is that means of replication do 

 exist and that they are precise enough to give both great stability 

 and appropriate freedom for change. Change is produced very 

 gradually over generations with the environment acting primarily 

 by means of selection. The environment normally does not alter 

 the DNA molecules, although it is ultimately responsible for the 

 rare and random genetic mutations. Rather, it selects one or 

 another set of these molecules in terms of the phenotypes produced 

 and of the relative degree of their adaptation to the environment. 

 This is Darwinian evolution — natural selection of certain molecules 

 from an array of possible DNA molecules or groups of molecules. 

 But when a given DNA molecule starts to operate in a given 

 organism, it produces messenger RNA and ribosome RNA and 

 proteins and enzymes and all tlie rest; and somehow or other this 

 sequence is under pretty direct control of the environment. Indeed, 

 it looks as if there is here a Lamarckian kind of influence by the 



