Sexual and Artificial Selection. 117 



ance. The disappearance of an old dominant type is hastened not only 

 by the adverse effects of new climatic and food conditions, but by the 

 natural hostility of the incoming new t3 r pe. If the old one is good for 

 food it will be eaten ; if it uses the same sort of food it will be in competi- 

 tion with the new comer and if less vigorous will be rapidly destroyed, 

 and in the process the victorious party will itself undergo modification. 

 If a race of animals suitable for the food of another is entirely consumed 

 and exterminated by it, the survivors must adopt a new bill of fare, 

 which may tend to still further modification of themselves. 



The action of man upon other animal races is probably more effectual 

 than that of any dominant type that has gone before, although in the 

 same direction. He has exterminated or contributed to the extermina- 

 tion of almost all the great herbivores and carnivores that ranged over 

 Europe and America in Tertiary times, and it is only a question of time 

 when he will do the same in Asia and Africa. But lie has selected for 

 survival a great number of tribes that he finds he can make useful to 

 himself the Horse, Ass, Camel, Elephant, Dog, Lama, Deer, Sheep, 

 Goat, Hog, Buffalo, Ox, Cat, Chicken, Goose, Pea-fowl, Guinea-fowl, 

 Turkey, Duck, Pigeon, Rabbit, Ferret, Falcon, Cormorant, &c. , have all 

 been domesticated wholly or partially, and made to contribute to the 

 needs of the dominant race. Many of these have been subjected to ar- 

 tificial differentiating causes, and then to repeated and long continued 

 selection, by which numerous varieties and breeds have been produced, 

 differing greatl} T from their original stocks and from each other. The 

 art of breeding cattle, horses, sheep, dogs and various fowls has been 

 known and practiced from time immemorial. The patriarch Jacob un- 

 derstood both the causes of variation and the theory of selection ac- 

 cording to Genesis, chapter thirty more than 3600 years ago. Great 

 stimulus has been given within the present century to artificial selection, 

 and rapid progress has been made both in actual results and in the 

 theory of it. It is now said that a breeder of sheep, for example, ma} T 

 chalk out on a wall such form as he prefers, and may, by selection, in a 

 few generations, copy the pattern in the form of his animals. Of 

 pigeons a skillful breeder said he could produce any given feather in 

 three years, and a given form of head or beak in six years. Darwin as- 

 serts that there are not less than twenty varieties of domestic pigeons 

 which if wild would be classed as so many species, which have all been 

 artificially differentiated by selection from the single species of Rock- 

 pigeon Columba livia. The variations from the original stock are 

 very great, extending to form, size, color, habits, and anatomical struc- 

 ture. The Fan tail has thirty or forty tail feathers, while the original 

 number is twelve or fourteen. "The Jacobin has the feathers so much 

 reversed along tho back of the neck that they form a hood." The 



