Problem of Human Heredity 149 



ability mated with ability tends to repro- 

 duce ability. The expert dairyman carefully 

 inquires into the purity of strain and ancestral 

 performance of the animal he mates with his 

 choice cows. The farmer insists on a hog with 

 certified ancestors. We have sense enough to 

 apply such knowledge of heredity as we possess 

 to our farm stock. It seems little enough to ask 

 that we should exercise as much good sense in 

 producing children as we do in the production 

 of hogs and corn. That does not mean that we 

 can apply the method of the cattle pen to 

 human relations, but merely that we adopt 

 caution and intelligent foresight in founding a 

 family commensurate with that used by the wise 

 breeder of plant or animal stock. 



Briefly, the knowledge now at our command 

 for this pmpose may be summarized as foUows. 

 Whenever plants or animals differing from each 

 other in one or more particulars are interbred, 

 the transmission of those factors, whose inter- 

 play determines the hereditary characters, is in 

 accordance (generation after generation) with 

 the simple MendeUan laws. Even those cases 



