104 A Century of Science 



blem, nor did he anywhere show clearly why 

 natural selection might not have gone on forever 

 producing one set of beings after another distin- 

 guishable chiefly by physical differences. But 

 Darwin's co-discoverer, Alfred Russel Wallace, at 

 an early stage in his researches, struck out a most 

 brilliant and pregnant suggestion. In that one 

 respect Wallace went further than ever Darwin 

 did. It was a point of which, indeed, Darwin 

 admitted the importance. It was a point of which 

 nobody could fail to understand the importance, 

 that in the course of the evolution of a very highly 

 organized animal, if there came a point at which it 

 was of more advantage to that animal to have vari- 

 ations in his intelligence seized upon and improved 

 by natural selection than to have physical changes 

 seized upon, then natural selection would begin 

 working almost exclusively upon that creature's 

 intelligence, and he would develop in intelligence 

 to a great extent, while his physical organism would 

 change but slightly. Now, that of course applied 

 to the case of man, who is changed physically but 

 very slightly from the apes, while he has traversed 

 intellectually such a stupendous chasm. 



As soon as this statement was made by Wallace, 

 it seemed to me to open up an entirely new world 

 of speculation. There was this enormous antiquity 



