24 GENETIC VARIATIONS 



the same combination of genes, all having the same hereditary 

 characteristics. 



It is through this method that is produced much of the 

 astonishing variety seen in cultivated plants. This is the 

 reason v^^hy the horticulturist is able to progress so much more 

 rapidly than the animal breeder in developing new types. By 

 mating together different strains he produces a great num- 

 ber of diverse combinations, some of them differing very 

 greatly from the original stocks. These combinations he 

 multiplies and makes permanent through reproduction from 

 the single parents — by cuttings, bulbs, and similar methods. 



But this method cannot be used w^ith the higher animals 

 and man. Here reproduction from two parents is the only 

 method. Every combination produced in one generation is 

 taken apart in the next. A slow and inefficient substitute for 

 uniparental reproduction in making the new combinations 

 permanent is found in inbreeding — the mating of close rela- 

 tives. Individuals having the same, or nearly the same combi- 

 nations of genes, are mated. Their offspring necessarily differ 

 much less from their parents and from one another in their 

 combinations of genes than in the usual case of mating be- 

 tween parents with very diverse sets of genes. By continuing 

 for many generations the mating of close relatives, stocks may 

 be produced that are nearly uniform and permanent — until 

 they are again crossed with other stocks. In this way even in 

 the higher animals stocks are producible that are lasting, and 

 that differ greatly from the stocks from which they took 

 origin. By selecting and isolating the best of these, great im- 

 provement can be brought about. Some time, some ruthless 

 race, like the Japanese, will apply this procedure to man, with 

 possibly startling results. 



Biparental reproduction and inheritance thus plays an im- 

 portant role in evolution. It brings about transformism, it 



