372 BIOLOGY AND ITS MAKERS 



mals, it has been determined that there was in that geological 

 period a marked increase in the size of the brain. This cir- 

 cumstance was of the greatest importance both for progress 

 and for perpetuity of certain kinds of animals. Those in 

 particular whose increased intelligence enabled them to cope 

 more successfully with the conditions of their existence, and 

 to turn natural forces to their advantage, were continued and 

 improved. In pre-humans the increase in brain surface led 

 to the power of storing up mental impressions and experi- 

 ences, and, finally, brought about a condition of educability 

 which formed the starting point for marked improvement. 



Mental Evolution. — Already the horizon is being wid- 

 ened, and new problems in human evolution have been opened. 

 The evidences in reference to the evolution of the human 

 body are so compelling as to be already generally accepted, 

 and we have now the question of evolution of mentality to 

 deal with. The progressive intelligence of animals is shown 

 to depend upon the structure of the brain and the nervous 

 system, and there exists such a finely graded series in this 

 respect that there is strong evidence of the derivation of hu- 

 man faculties from brute faculties. 



Sweep of the Doctrine of Evolution. — The great sweep 

 of the doctrine of evolution makes it "one of the greatest 

 acquisitions of human knowledge." There has been no 

 point of intellectual vantage reached which is more inspiring. 

 It is so comprehensive that it enters into all realms of thought. 

 Weismann expresses the opinion that "the theory of descent 

 is the most progressive step that has been taken in the devel- 

 opment of human knowledge," and says that this position 

 "is justified, it seems to me, even by this fact alone: that the 

 evolution idea is not merely a new light on the special region 

 of biological sciences, zoology and botany, but is of quite 

 general importance. The conception of an evolution of life 

 upon the earth reaches far beyond the bounds of any sin- 



