458 TKADITION AND HEKEDITY 



and others speak of differential fertility as the origin of the 

 cyclical course of civilization, what they in fact attribute to this 

 cause are the periods of decline. Other causes are sought for 

 to account for the equally remarkable periods of advance. 

 Mr. McDougall, for instance, attributes the rise of Greek civiliza- 

 tion to a ' happy blending ' of two races. 1 It may be said, on the 

 other hand, that the facts point strongly to the conclusion that 

 both the * ups ' and the ' downs ' are part of the same pheno- 

 menon. The ' ups ' are as remarkable as the ' downs ' ; one 

 process seems just the reverse of the other. No one proposes to 

 explain the ' ups ' as due to the favourable results of differential 

 fertility, and before we can accept unfavourable differential 

 fertility as the chief cause of the * downs ' we may ask if the 

 fundamental cause of both processes is not of another kind. If 

 we should find this to be the case, it of course by no means implies 

 that germinal change does not play a contributory part. 



13. The greater part of the discussion in this chapter has been 

 devoted to an attempt to estimate the importance of germinal 

 differences and of germinal changes ; it is clear that in order to 

 arrive at more definite conclusions we have to consider in rather 

 more detail traditional differences and traditional changes. The 

 influence of the direct effect of the environment must not be 

 forgotten, as it frequently enters as a contributory factor into the 

 moulding of the course of history. It may conveniently be con- 

 sidered here. 



Temperament is a characteristic of great importance. Just as 

 among men around us temperament is seen to influence each 

 man's achievement, and largely to determine failure or success, 

 so racial temperament is important in determining racial achieve- 

 ment. This characteristic is peculiarly sensitive to the direct 

 effect of the environment, and it may very well be that 

 changes in diet and so on may have influenced the course 

 of history through their bearing upon temperament. At the 

 present day the urban conditions under which so large a percentage 

 of the members of western nations live smoke, noise, vibration, 

 and so on may have a bearing upon temperament and so upon 

 achievement. 



Such considerations are somewhat speculative. More clear are 

 the results of disease upon temperament. It is a remarkable fact 

 1 McDougall, Group Mind, p. 247. 



