18 WHAT IS EUGENICS? 



from their grandparents. Hereditary qualities, when 

 transmitted to another generation, remain unchanged ; 

 though they may be sorted out differently. Somewhat the 

 same bodily and mental qualities will often keep cropping 

 out in successive generations, and yet members of the same 

 family will differ considerably amongst themselves. Fact 

 and theory hang together perfectly. 



The fact that each hereditary quality of any individual 

 is passed on to some but not to all of his descendants shows 

 its results in the following way also. We have seen that 

 we cannot foretell what will be the qualities of a man 

 before he is born. But if we know the qualities of his near 

 relations we can tell a good deal about what his qualities 

 will probably be. This means that, though we should 

 make many bad shots, we should be generally far nearer 

 the truth than if we went by chance. 



Perhaps a single example may make this point clearer. 

 Let a thousand fathers be selected, all four inches above the 

 average height of the nation as a whole. Now, we cannot 

 know what will be the height of any one of the sons of these 

 fathers. We do know, however, with considerable accuracy 

 that if a large number of these sons were to be measured, 

 they would prove to be on the average two inches above the 

 average height of the nation, or about half the excess of 

 their parents. And this is true of most or all other qualities 

 that can be measured. This being the case, when a farmer 

 is breeding cattle, he is often disappointed in regard to 

 particular beasts. He never doubts, however, that by care 

 in breeding he will raise the qualities of his stocks to some 

 extent. And this is equally true as regards the breeding 

 of men. 



We have seen that the sons of fathers selected on account 

 of their height, though tall, will not be as tall as their 

 fathers. This fact is known as the regression to the mean. 

 Now, this regression does not continue beyond a certain 

 point. It does not destroy the benefits arising from 

 selection in breeding. If a number of tall sons and daughters 

 of a selected group of parents were to be kept as a caste 



