XII. THE EVOLUTION OF MANKIND AND ITS FUTURE 421 



the inactivation progresses rapidly at first, but later distinctly slows 

 down presumably because of the increase in the intensity of the repul- 

 sive force. 



The bending force of the inactivating agents, on the other hand, 

 should be determined by the kind of the agents, and in one and the 

 same agent, the higher the concentration the more rapid and the more 

 extensive may be the change. The change of rennin due to antiserum 

 or tannin in low concentrations appears usually to cease to proceed 

 after some periods of progress, whereas the inactivation due to heat 

 proceeds without diminishing the velocity until the inactivation be- 

 comes completed. Thus heat is regarded as an agent strong enough to 

 be able to ignore the repulsive force. 



In the case of phage, formalin acts as a strong agent, so that 

 almost no diminution in the velocity is observed as already shown in 

 Fig. 35, whereas some diminution is seen with HgClj or with heat, 

 and in both cases of antiserum and tannin diminution is usually mani- 

 fest (62). It may be said, therefore, that, if the force to push forward 

 the change is much greater than the repulsive force, the change will 

 proceed without decreasing, whilst if the former force is weak, the 

 repulsive force will be revealed to diminish the changing velocity. 



Presumably this holds true for the change of genes. The effect 

 of environment including climate seems to exert its action comparatively 

 rapidly on human genes as shown in the above cited observations of 

 Boas, but a considerable span of time may be necessary for the immi- 

 grants from various parts to become an entirely similar type, if possible, 

 which is to be determined by the environment of the settlement. 



Here a great question may arise. If the repulsive force of the 

 genes becomes greater as the change proceeds, the change is expected 

 to be suspended sooner or later. If so, evolution is impossible unless 

 the environmental factor is strong enough to disregard the force. Is 

 this ever the case ? 



Here again we should remember the nature of the reversibility of 

 protein structure. The reversibility depends upon the memory of the 

 former structure. Therefore, the loss of the memory may result in 

 the disappearance of the repulsive force, and consequently if a gene is 

 left for a long time in the same changed state under the same en- 

 vironment causing the change, its former structure will be forgotten 

 with the disappearance of the repulsive force, the change thus being 

 gradually pushed forward. This seems not only the case with genes, 

 but also with elastic substances in general. The organic evolution as 

 already stated cannot take place unless the memory of the former 

 structure is lessened or lost. 



Proteins can thus be looked upon as an elastic substance and the 



