210 SCIENCE AND THE HUMAN MIND 



burgh with the idea of medicine, and at Christ's 

 College, Cambridge, when he intended to take Holy 

 Orders, Darwin got his best training as a naturalist 

 on the five years' voyage of the Beagle in South 

 American waters. In tropical and subtropical lands, 

 teeming with life, Darwin received the impression of 

 the interdependence of all living things, and within 

 a year of his return he began to compile the first of 

 his note-books on the facts bearing on the transmuta- 

 tion of species, led thereto by his study of South Ameri- 

 can fossils. Fifteen months later he read Malthus' 

 book, and found the clue which enabled him to frame 

 a theory of the means whereby new species might 

 develop. 



The individuals of a race differ from each other in 

 innate qualities. If the pressure of existence or the 

 competition for mates be great, any quality which 

 is of use in the struggle for life or mate has " survival 

 value," and gives its possessor an advantage which 

 carries with it an improved chance of prolonging life, 

 or of securing a mate and of rearing successfully a pre- 

 ponderating number of offspring to inherit the favour- 

 able variation. That particular quality therefore tends 

 to spread throughout the race by the progressive 

 elimination of those individuals who do not possess it. 

 The race is modified, and a different and permanent 

 variety may slowly be established. This was the 

 new conception ; and it was well put by Thomas Henry 

 Huxley, who by his power of exposition, skill in 

 dialectic and courage in controversy did more than 

 any other man to compel general acceptance for the 

 views of Darwin and Wallace : " The suggestion that 

 new species may result from the selective action of 



