HERITAGE OF THE INDIVIDUAL 



301 



each of which contributes its slight and variable quota to the 

 expression in a given individual. (Figs. 154, 155.) 



The question is, what results are obtained by breeding from 

 individuals which exhibit such a fluctuating variation to, 

 let us say, a greater degree than that of the mean of a mixed 

 population? The reader with Galton's theory of filial regres- 



A B 



Fio. 154. Model to illustrate the law of probability, or chance. A, shot field in 

 the funnel at the top of the board; B, the shot, released by opening the mouth of the 

 funnel, have fallen through the series of hazards (pins), and been deflected by 'chance' 

 into the vertical compartments at the bottom. The curve connecting the tops of the 

 columns of shot is the normal probability, or frequency, curve. (After Kellicott.)- 



sion in mind will naturally expect, and rightly, that the off- 

 spring usually will exhibit the character to a less degree than 

 the parents but to a greater degree than the population. The 

 top (mode) of the curve will have moved, so to speak, slightly 

 in the direction of selection. Now, by continuing generation 

 after generation to select as parents the extreme individuals, 

 is it possible, with due allowance for some regression, to take 

 one step after another indefinitely, or until the character in 

 question is expressed to a degree which did not exist previ- 



