418 EVIDENCES OF EVOLUTION 



widely separated, as in the case of the family of camels, 

 past migrations with the extinction of individuals in the 

 intervening territory are responsible. In short, all of 

 the facts of geographical distribution are satisfactorily 

 explained by evolution. Otherwise they are a senseless 

 jumble. 



Artificial Selection. — That animals and plants are 

 not rigidly fixed but on the contrary are capable of change 

 is known to every breeder. (Chap. XXXIII) He decides 

 upon some character — a special form, color, or quality — 

 and selects those individuals which manifest it in the 

 highest degree. The survivors in the selection process 

 are then bred, the most desirable members are again 

 selected and bred, and so on, generation after generation. 

 " It would seem as if they had just chalked on the wall 

 a form perfect in itself and then had given it existence. " 



The two hundred and more breeds of the domestic 

 pigeon have been derived from the rock pigeon of Europe 

 and Asia by artificial selection. The many varieties of 

 domesticated fowls are the artificially selected descend- 

 ants of the jungle fowl of India, which has been bred for 

 more than three thousand years. Sheep, cattle, and hogs, 

 pansies, tulips, dahlias, and many other cultivated flowers 

 as well as numerous garden vegetables, are likewise 

 greatly altered descendants of the original wild stocks. 

 But while man is thus able to mold a species into many 

 distinct varieties, there is a wide diff'erence in one respect 

 between his results and those obtained under natural con- 

 ditions. If these domesticated breeds are allowed to es- 

 cape and come into competition with wild species, they 

 are usually exterminated. Evidently, the characters de- 

 sired by man are not necessarily those that best fit their 

 possessors to compete successfully with wild forms. 

 There is, however, a general similarity between the arti- 

 ficial and natural production of species, as will appear 

 in the next chapter. And furthermore, the evidence 

 supplied by these breeding operations not only demon- 



