108 A Century of Science 



being developed and his form is taking on its out- 

 lines. During prenatal life there is not time 

 enough for all these nervous registrations, and so 

 by degrees it comes about that he is born with his 

 nervous system perfectly capable only of making 

 him breathe and digest food, of making him do 

 the things absolutely requisite for supporting life ; 

 instead of being born with a certain number of 

 definite developed capacities, he has a number of 

 potentialities which have got to be roused accord- 

 ing to his own individual experience. Pursuing 

 that line of thought, it began after a while to seem 

 clear to me that the infancy of the animal in a very 

 undeveloped condition, with the larger part of his 

 faculties in potentiality rather than in actuality, 

 was a direct result of the increase of intelligence, 

 and I began to see that now we have two steps : 

 first, natural selection goes on increasing the intel- 

 ligence ; and secondly, when the intelligence goes 

 far enough, it makes a longer infancy, a creature 

 is born less developed, and therefore there comes 

 this plastic period during which he is more teach- 

 able. The capacity for progress begins to come 

 in, and you begin to get at one of the great 

 points in which man is distinguished from the 

 lower animals, for one of those points is undoubt- 

 edly his progressiveness ; and I think that any one 



