12 Heredity and Eugenics 



reached in a thoroughly scientific way, Darwin 's conception 

 was based upon an amount and range of observation hitherto 

 unapproached; so that if Lamarck's approach was scien- 

 tific, Darwin's was still more scientific. In fact, Darwin's 

 announcement came at a psychological moment, which 

 enormously reinforced his message; and this is not detract- 

 ing in the least from the power and beauty of its presenta- 

 tion. Whether Darwin's explanation stands or falls, his 

 supreme contribution must be regarded as the introduction 

 of a point of view and a method of attack that not only 

 ushered in modern biology, but also revolutionized thought 

 in general. 



Natural selection is too familiar to need extended expla- 

 nation. The ratio of increase of organisms, leading to 

 over-production and a struggle for existence, resulting in 

 the survival of the fittest, is a series of exceedingly familiar 

 phrases, not all of which should be attributed to Darwin. 

 That plants and animals can be led along in any desired 

 direction was proved by experimental evidence obtained 

 from the operations of plant and animal breeders ; and since 

 this guidance of plants and animals by man was by means 

 of selection, it was most appropriate to call the guidance 

 by nature "natural selection." 



The most significant fact connected with this theory 

 remains to be mentioned, and that is the fact of variation. 

 Nothing is more clear than that any machinery of evolution 

 must depend upon this fact. Darwin greatly enlarged the 

 horizon of our knowledge in reference to variation. It is 

 variation that gives rise to individuality among plants and 

 animals, so that no two plants or animals are exactly alike. 

 We have accustomed ourselves to individuality among 

 human beings, for we have been trained to note the dis- 



