APPLICATION OF STATISTICAL METHODS 311 



connects them. Thus, while every one Lnows that the stature 

 attained by a thousand young men depends upon a multitude 

 of dimensions of different parts of the body, and that these 

 dimensions depend on numerous conditions, of which food is one, 

 climate another, and parentage a third, we owe it to statistical 

 methods that we are able to say definitely what relation 

 the average height of these thousand sons bears to the average 

 height of their fathers, that we are able to say, furthermore, 

 that their stature depends more on the stature of their fathers 

 than on that of their mothers. Thus we get a solid foundation 

 for further inquiries of a deeper sort. 



Again, to take another illustration, we know enough in regard 

 to the results of four thousand throws of approximately sym- 

 metrical dice, to be able to say dogmatically, in regard to the 

 quite divergent results of four thousand throws of other dice, 

 that the latter must have been loaded. Similarly, as our know- 

 ledge of the laws of the random grows, we become able to detect 

 when Nature's dice are loaded. 



It should be clearly understood that the generalisation 

 "Like begets like" may be much truer for the race at any 

 given time than for any one relation of parents and offspring. 

 Processes of selection in many forms tend to prune off pecu- 

 liarities — operating even before birth, operating in very early 

 stages of independent life, and never ceasing to operate — and 

 thus one generation of a race may be very like the preceding 

 generation, although in cases of individual heredity there may 

 be marked differences between offspring and their parents. In 

 short, it is very important to realise the distinction between 

 individual heredity and race-heredity. The statistical study of 

 inheritance enables us to do this. 



§ 2. Historical Note 



In order to appreciate the statistical point of view and the 

 general ideas underlying its methods, the reader is advised to 



