170 THE FIRST PRINCIPLES OF HEREDITY 



" We see," says Pearson, " selection is not checked by 

 regression. Regression is merely the result of mediocre 

 ancestry ; the moment we give selected ancestry, the 

 regression begins to diminish, and in a few generations is 

 hardly sensible." 



If, however, selection stops and general inbreeding of 

 the selected stock takes place, decline at once sets in. 

 The ratios have been calculated by Pearson as follows, 

 according as selection stops after the first, second, third, 

 or tenth generation of selection. We give the values for 

 the first and last cases above mentioned : 



Last. 

 Generation. 



0*92 h. 



0-86 h. 

 o-8i h. 

 077 h. 

 0-51 h. 



A most important conclusion follows from the considera- 

 tion of the above results. While we have seen that an 

 exceptional characteristic arising from mediocre ancestry 

 is bound to revert within a few generations to the general 

 level of mediocrity displayed by those ancestors, it becomes 

 apparent that, if the characteristic be selected for a number 

 of generations, it will, with continued selection, breed true 

 in all successive generations within i per cent, of its 

 original value. 



As Galton has expressed it : "A fundamental distinction 

 may exist between two couples whose personal faculties are 

 naturally alike. If one of the couples consists of two 

 gifted members of a poor stock, and the other of two 

 ordinary members of a gifted stock, the difference between 

 them will betray itself in their offspring. The children 

 of the former will tend to regress, those of the latter will 

 not. \ The value of a good stock to the well-being of future 

 generations is therefore obvious." It follows from this 



