CHAPTER VIII 



THE INHERITANCE OF PHYSIC.\L AND MENT.AL TRAITS 

 OF MAN AND THEIR APPLICATION TO EUGENICS 



The general laws of heredity have already been fully 

 explained. But every person has a different way of express- 

 ing them and a little repetition wall do no harm; and so, 

 very briefly, I will recapitulate the principles of heredity. 



First of all, we find useful the principle of the unit- 

 character. Whether it be ultimately accepted or discarded, 

 it is useful today, and so we accept it as a guiding hypothesis. 

 According to this principle characters are, for the most part, 

 inherited independently of each other, and each trait is 

 inherited as a unit or may be broken up into characters 

 that are so inherited. 



Next it must be recognized that characters, as such, are 

 not inherited. Strictly, my son has not my nose, because 

 I still have it; what was transmitted was something that 

 determined the shape of his nose, and that is called in 

 brief a "determiner. " So the second principle is that unit- 

 characters are inherited through determiners in the germ 

 cells. 



And finally, it is recognized that there really is no inherit- 

 ance from parent to child, but that parent and child 

 resemble each other because they are derived from the 

 same germ plasm, they are chips from the same old block; 

 and the son is the half-brother to his father, by another 

 mother. 



These three principles are the three cornerstones of 

 heredity as we know it today, the principles of the inde- 



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