154 Inside the Living Cell 



to be better to have a continuous stream of new and vigorous persons 

 than to extend the individual life period considerably. If the average 

 life span were, say, 120 or 150 years, the whole tempo of life would be 

 different. Education would continue up to the age of 30 or 40; full 

 maturity from 40 to 100 or 120 and a gradual decline into old age from 

 the age of 100 upwards. It is not at all certain that this would produce 

 any improvement on the present conditions. It would greatly reduce 

 the tempo of change in human Hfe. There would not be the same urge 

 to get things done. Young men would have to wait very much longer 

 for their chances. Many of the eminent people who died during the 

 last fifty years would still be alive and probably, if their health were 

 reasonably good, occupying the same posts which they held in about 

 1910 to 1920. The result would be that in the end the longer life span 

 would produce exactly the same problems and difficulties as the 

 present one. Indeed it seems likely that the present span of life is rea- 

 sonable in relation to and perhaps determined by the speed of human 

 life processes. The normal span is already long enough for individuals 

 to develop their potentialities to a reasonable extent and to give a 

 sufficient balance between initiative and experience, which is required 

 if human society is to be neither stagnant nor juvenile. Of course, it is 

 likely that under existing condhions a great many people do not suc- 

 ceed in developing their full possibilities, but this is a fault of the org- 

 anization of society, which does not offer sufficient opportunities for 

 development, rather than of the time available. The people who have 

 not developed a satisfying life or have not found out how to use their 

 full abilities during their first sixty years are unlikely to do much 

 better with another thirty or forty. 



One other possibility may be mentioned — that one factor which 

 limits the possible development of human beings and therefore their 

 valuable life, is the quantity of brain available. There may be a limit 

 to the number of new impressions which a brain can effectively uti- 

 lize. It seems to be a general experience that the ability to entertain 

 new ideas and absorb new experiences diminishes with advancing 

 age. New experiences have to be assimilated into the accumulated 

 patterns of experience that have been developing throughout life. 

 Older people often find it difficult to adapt their thinking to new con- 

 ditions and to the new ideas of a new generation. This is because their 

 thinking is organized around conceptions which are no longer valid — 

 their brains in fact contain great organizations of experience which 

 are no longer of any value, because the circumstances they were 

 based on have passed away. The structure of their brains does not 

 permit them to cast away all this now useless lumber and start again. 

 The only way in fact in which they could start again is by being re- 



