EVOLUTION OF MAN loi 



acters which it causes to survive in the struggle for 

 existence shall be maintained at a fairly general level 

 of efficiency. This is so because excessive variation 

 from the common standard must result either in de- 

 ficiency or in disturbance of organic balance; and 

 either of these results will cause non-survival in the 

 struggle. This law holds good in the lower species, 

 the vigorous members of which do not vary in their 

 characters more than one-sixth to one-fifth from a 

 common standard. But the case is quite otherwise 

 with human beings. Men are found to vary to an 

 astonishing degree, both in the positive and in the 

 negative direction, in their possession of the higher 

 faculties; and this excessive variation usually has no 

 visible effect upon the persistent vitality of either the 

 individual members of the species or of the species as 

 a whole. These higher faculties, therefore, seem to be 

 independent of the law of natural selection in their 

 origin and development.^ The force of these two 

 arguments depends to some extent, of course, upon the 

 Darwinian supposition that in natural evolution species 

 are chiefly formed by natural selection. The argu- 

 ments which I am about to mention are valid in relation 

 to any purely physical theory of evolution. 



In passing, however, permit me to state Mr. Wallace's 

 general conclusion. He discovers three stages in evo- 

 lution, at which variations occur that are too great and 

 too sudden to be accounted for by the accumulation 

 of slight and continuous variations and the working of 



^ Op. cit., pp. 269-272. 



