16 INBREEDING AND OUTBREEDING 



body politic due to differential fecundity, birth control, 

 and other agencies by which the character of the popula- 

 tion is shifted ; they even have some relevancy to many 

 problems which one might suppose were wholly of an 

 economic nature, such as minimum wages and mothers' 

 pensions. 



The second series of phenomena arousing interest in 

 the results of inbreeding and outbreeding comes from ob- 

 servation upon domestic animals and cultivated plants. 

 Plants are included by courtesy, though in reality intelli- 

 gent plant breeding hardly began until the nineteenth cen- 

 tury, and the methods adopted were taken from the pro- 

 cedures in use by animal breeders, with such modifications 

 and improvements as the peculiarities inherent in vegeta- 

 tive propagation made necessary. Animal breeding, on 

 the other hand, is a very ancient occupation, and more or 

 less accurate data on the effects of interbreeding near 

 relatives as compared with the effects of crossing differ- 

 ent strains must have been collected by all of the old 

 agricultural peoples. Since there is no question that 

 under certain circumstances inbreeding does produce un- 

 desirable results defectives, dwarf-forms, sterile indi- 

 viduals, etc. it may be that their experience was at the 

 base of some of the antagonism toward close-mating in 

 the human race. Or, it is possible that early breeders ob- 

 served the phenomenon, common to both animals and 

 plants, that when two unrelated stocks are crossed the hy- 

 brids thus produced are often more vigorous than either 

 parent the phenomenon of hybrid vigor or heterosis, as 

 it is called at the present time. There is no proof of such a 

 sequence of ideas, but it seems to be a logical hypothesis. 

 At any rate, the views of the animal raisers regarding 



