CHAPTER X 

 THE MECHANISM OF EVOLUTION 



1. The Evolution without Natural Selection 



An alteration of the environment results in a change in the char- 

 acter of the organism. The change thus raised is mostly favourable 

 for the organism and will be advanced as long as the environmental 

 factor to induce the change continues to exist, until at last the changed 

 character becomes fixed and inheritable. For example, if a mammal 

 is kept under the environment of a high temperature, its tail and ears 

 will become long and expanded as shown by the Sumner's experiment 

 Avith rats as above cited. Such a change is indeed significant for the 

 temperature regulation, and hence the mammal is said to have adapted 

 itself to the high temperature. If the mammal is kept under such a 

 high temperature for successive generations, the acquired character 

 will become hardly reversible and fixed so as to be inheritable. 



According to the experiment of Sumner, some of the rats exposed 

 to high temperatures for only one generation tended to transmit the 

 character to the progeny. The phenomenon, known as Allen's rule, 

 that mammals of the warmer climates expand body surfaces by the 

 development of parts, such as ears and tails, may be the result of this 

 adaptation fixed by Nature. Here, it should be realized that such 

 adaptive evolution is possible to occur without any natural selection, 

 that is, organisms can evolve without natural selection in adapting 

 themselves to environments. 



The evolution must be far more rapid and easier if the effect of 

 use is added to the environmental factor. Thus, if a tail, lengthened 

 by a high temperature, can be used to grasp objects and if its use is 

 required, the animal will use it repeatedly and this effect of use will 

 be added to the influence of the temperature to develop the tail ex- 

 tensively. In such a way, tails of certain animals such as monkeys 

 and rats have probably developed. 



The stimulus resulting from the use would become greater, the 

 higher the organ was advanced, because of the more unusual and 

 incessant use, and therefore the development of the organ would be 

 advanced unlimitedly unless it ceased to be used. Orthogenesis may 

 be thus established. Natural selection may help more or less the 



