242 INITIATIVE IN EVOLUTION 



nervous integration with growing control over their environments. 

 The long story from the simple central nervous system of a fish, 

 with a few or no association-areas, to that of man with his extensive 

 frontal, parietal, parieto-occipital association-areas, could never 

 be deciphered, even with the light of the laws of genetics turned 

 on full, without a protracted process of construction of fresh arcs. 

 A common illustration of such a series of changes and results may 

 be seen in the building of a house. Bricks, foundation-stones, 

 walls and a roof may serve some of the elementary requirements 

 of a house and much less than these were of use to early man for 

 his shelter. Without them we cannot call any structure a modern 

 house ; but also without floors, staircases, windows, chimneys, 

 division into rooms, some degree of decoration by paint or paper, 

 and a supply of water, we should refuse in these days the name of 

 house to that rough structure, apart from beauty of design, decora- 

 tion, within and without, and some addition of modern appliances 

 of comfort and convenience. In the history of house-building the 

 stages of supply of raw materials, adaptation to needs guided by 

 selection, initiation, trial and error have their counterpart in the 

 construction of higher animals. 



Evidence. 



It will be asked what evidence there is for the view here put 

 forward that such is the order and method of the construction of 

 the central nervous system. There are two classes of evidence. 

 The first direct, and the second indirect and resting on inference. 

 The well-known leads to the less-known and inferred. Direct 

 evidence of the foundation of new reflex -arcs and their organization 

 is of course small. The conditions, such as the duration of human 

 life, preclude any extensive formation under experiment of new 

 reflex -arcs, but enough is known to enable one to follow the back- 

 ward way with some confidence. As to the inheritance of these, 

 the evidence rests on opinion and tremendous probability, but as 

 the only problem with which I am concerned here is that of initiative 

 I think it better to leave the matter of transmission to a dispassionate 

 consideration of the probability of its occurrence. 



Direct Evidence. 



The prolonged researches of over twelve years of Professor 

 Pawlow and his colleagues on dogs afford a body of evidence as to 

 the possibility of producing new reflexes in the life of an individual 

 which have never been questioned. In 1913 at Groningen, before 

 the International Congress of Physiologists, he gave a brief account 



