Artificial Creation of Species 177. 



New Creations 



We have learned in recent times a great deal about the 

 effects of hybridizing and the reasons for the apparent in- 

 stability of hybrid types (see page 254). A part of this 

 understanding enables us at least to anticipate the behavior 

 of seemingly new plant or animal forms which are the result 

 of hybridization. They enable us with greater certainty to 

 establish pure lines in which a desired character — for ex- 

 ample the absence of horns in cattle — may be assured 

 in successive generations. We have then at hand a means 

 of controlling plant and animal breeding so that not only 

 can new qualities that present themselves be preserved but 

 new combinations of qualities can be produced to order. 



To say that variation may result from hybridizing is 

 to point to one method by which variation is brought about : 

 it does not affect the significance of the variation as a possi- 

 ble step in evolution. It does raise again, however, the ques- 

 tion of the traditional assumption that distinct species are 

 sterile when mated. We have seen (page 68) that animals 

 of distinct species, even of distinct genera, may be made to 

 breed together. The same is true of many distinct types of 

 plants. On the other hand, cultivated varieties of what are 

 commonly accepted to be the sa^ne species are often sterile 

 when mated. 



When it comes to the variations observed among do- 

 mesticated animals and the establishment of new breeds by 

 selection and segregation, we are not distracted by the ques- 

 tion of propagation. These animals all reproduce sexually 

 and we are not long left in doubt whether given characteris- 

 tics reproduce themselves in succeeding generations. We are 

 familiar with new breeds of dogs and cats, cows and horses, 

 sheep and pigs, poultry and pigeons, to say nothing of the 

 numerous breeds of fancy or pet animals that have no direct 

 economic importance. These indicate that, starting with 

 variations, it is possible to establish numerous strains from a 

 common ancestry. Animals that differ more from each other 



