62 BASIS OF INVESTIGATION. 



occur chronologically, or take them in any other manner that does 

 not partake of selection in the biological sense, and from this one 

 thousand determine the kind and extent of variations, then the 

 standard so established will be a very accurate index of the kind 

 and extent of variations in any other one thousand births selected 

 from any class of people in any part of the world. It would be as 

 true for the lower class as for the higher class, because the extent 

 of variation arising at a birth would be measured from the class in 

 which the birth occurred, and there is no reason for thinking that 

 variations would occur more frequently in one class than in an- 

 other. In nine-tenths of the cases the variations would be very 

 slight and not depart from the ancestral standard in a noticeable de- 

 gree. In one-tenth the variations would be quite noticeable and 

 would be divided equally between variations above and variations 

 below the ancestral standard. In one case in one hundred the va- 

 riation would be great, and in one in one thousand the variation 

 would be extraordinary. Variations in one direction are usually 

 followed by variations in the opposite direction, so that a class of 

 people having a given standard of mental power will persist in 

 maintaining that standard through many generations. 



DIFFERENT CLASSES. 



When, in any community, there exist two classes of individuals, 

 if one class increase in numbers faster than the other class, either 

 through earlier marriages, more prolific marriages, or both, then 

 it is only a question of time when the rapidly increasing class will 

 absorb the less rapidly increasing one. This may be illustrated by 

 a few figures. Assuming a community composed of one thousand 

 blacks, and one thousand whites, if the whites increase in numbers 

 at the rate of ten per cent during each decade, and the blacks increase 



