410 V. THE NATURE OF EVOLUTION 



trifling, if exists, and the Echinodermata which may be the oldest pri- 

 mary organisms are being adopted by them as the host (83). 



3. The Survival of the Fittest 



As we have seen above, natural selection appears not so important 

 for the evolution of the higher organisms as customarily believed, but 

 the selection may play sometimes a prominent role in the determination 

 of the direction of evolution. 



The genes are provided with the property to achieve the gradual 

 change in a certain direction. However, as the genes have the indivi- 

 duality, even under the same environmental effect every gene will 

 behave differently, changing in different rates and in different directions. 

 Nature will select the- gene which has been changed in the most fitted 

 way to the environment. As the gene thus selected may have the 

 property to continue the change favourable for the organisms, the or- 

 ganisms having the gene will continue the favourable change as long 

 as the environmental effect in question remains in existence. 



For example, if a colour change brought about in an insect under 

 a certain envii-onment becomes significant as a mimicry, the insect will 

 be selected and separated from other individuals, and since the insect 

 thus selected has the property to advance the colour change and, in 

 addition, since the selection will continue without resting, the mimicry 

 will sooner or later be completed, although it may be possible that the 

 change may go so far as becomes useless as mimicry. 



If herbivorous animals need fleetness in order to escape from their 

 enemies, by which the slower-footed individuals are to be devoured up, 

 the swifter-footed individuals will be selected and separated from the 

 original type. Since the selected individuals may have the tendency 

 to develop the character, the fleetness will gradually increase even 

 without further selection, but the continual enforcement to the use and 

 the successive selection in each generation will no doubt accelerate the 

 development. Thus, swift-footed animals like horses have presumably 

 been created. 



The phenomenon known as vernalization can be regarded as result- 

 ing from the natural selection by which a character fitted to a peculiar 

 environment has been adopted and developed. As is well recognized, 

 spring rye, in common with other spring cereals, requires no low tem- 

 peratures during germination for normal flowering, vv'hereas winter 

 rye, unless exposed to low temperatures during germination, as is 

 known as vernalization, shows a great delay in ear formation and 

 emergence. 



