104 THE NEW PHYSIOLOGY. 



not to criticise Darwin's account of the probable origin 

 of species, but to consider how far this account gives 

 support to the mechanistic theory of life. 



Darwin's argument, briefly put, is as follows. Among 

 all classes of organisms there occur variations, however 

 slight, from the average type ; and these variations, 

 in accordance with the law of hereditary transmission, 

 tend to be transmitted to offspring. Some of the 

 variations will give the individuals, or their progeny, 

 an advantage in the struggle for existence — a struggle 

 which is constantly going on, and in which, on the whole, 

 but few survive to the reproductive stage out of the 

 germ-cells from each, or each pair, of which the individual 

 develops. As a consequence, the variations which carry 

 with them an advantage in the struggle of the species 

 for existence will tend to survive, and the species will 

 tend to vary as a whole in the corresponding directions. 

 In this way, therefore, a species will, if there is possibility 

 of advantageous alteration, tend to vary as a whole ; 

 and under different local conditions of environment 

 the variations will, of course, take different directions, 

 thus producing a variety of species. 



Darwin supported his argument by a wealth of con- 

 crete observations, taken largely from the experience 

 of breeders of animals and plants under conditions of 

 domestication. It is no wonder that he has convinced 

 the world that species have arisen by development ; 

 and I should be the last to doubt this conclusion. But 

 the Darwinian theory has been taken as a support for 

 the mechanistic theory of life. It seemed to his genera- 

 tion to be a tracing of life back towards the mechanical 

 conditions which are at present pictured as existing in 



