FACTORS OF DARWIN'S THEORY 421 



four hundred years after the beginning of the revival of 

 learning naturalists had accumulated a vast amount of 

 unrelated information in many different fields, and had 

 developed to a considerable degree the modern sciences of 

 anatomy, embryology, physiology, geographical distri- 

 bution, classification, and microscopy. In the more re- 

 mote departments of history, language, religion, politics, 

 etc., there was also a huge mass of unrelated observations, 

 unrelated for the reason that the underlying fact of evolu- 

 tion had not been proved and accordingly was not gener- 

 ally considered to be even a remote- possibility. 



At the present time it is difficult to picture the influ- 

 ence upon human thought of Darwin's theory of evolu- 

 tion. His first work, " The Origin of Species," appeared 

 in 1859. It was based upon more than twenty years of 

 careful observation, was clearly and fairly presented, with 

 proofs at every stage, and in the face of bitter opposition 

 was accepted by the open-minded student. Under its in- 

 fluence very many questions of the most puzzling charac- 

 ter were made plain, and the flood of light which was let 

 in on the intellectual world at that period has increased 

 with each successive year. The time was more than ripe 

 for the fact of evolution to be recognized, and it is not 

 to be marvelled at that Darwin is hailed as the greatest 

 scientist the world has ever known. 



Factors of Darwin's Theory. — The Darwinian the- 

 ory of evolution, which is also termed Natural Selection 

 or the Survival of the Fittest, involves several different 

 factors. The first of these is (a) over-production. All 

 animals and plants produce a far greater number of off- 

 spring than can survive, owing to lack of space or food. 

 Since (b) the number of individuals remains about the 

 same from century to century, it follows that (c) there 

 is a struggle for existence. Furthermore, there is (c?) 

 variation (i.e., mutation) and (e) heredity. No two or- 

 ganisms are exactly alike, and many of these differences 

 are transmitted from one generation to the next. The 



