Darwin was particularly impressed by the way mankind has dealt with the various species of domesticated animals, and he was the first naturalist to point out the correspondence between the breeder’s method of “artificial selection,” and the world-wide process of natural selection.  As every one knows, the breeder of race horses finds that colts vary much in their speed; discarding the slower animals, he uses only the swifter for breeding purposes, and so he perfects one type of horse.  With other objects in view, the heavy draught horse, the spirited hackney, and the agile polo pony have been severally bred by exactly the same method.  Among cattle many kinds occur, again the products of an artificial or human selection; hornless breeds have been originated, as well as others with wide-spreading or sharply curved horns; the Holstein has been bred for an abundant supply of milk as an object, while Jerseys and Alderneys excel in the rich quality of their milk.  Various kinds of domesticated sheep and rabbits and cats also owe their existence to the employment of the selfsame method, unconsciously copied by man from nature; for men have found variations arising naturally among their domesticated animals, and they have simply substituted their practical purposes or their fancy for nature’s criterion of adaptive fitness, preserving those that they wish to perfect and eliminating those unfitted to their requirements or ideas.

In the case of many of these and other examples, wild forms still occur which seem to be like the ancestral stock from which the domesticated forms have been produced.  All the varied forms of dogs—­from mastiff to toy-terrier, and from greyhound to dachshund and bulldog—­find their prototypes in wild carnivora like the wolf and jackal.  In Asia and Malaysia the jungle fowl still lives, while its domesticated descendants have altered under human direction to become the diverse strains of the barnyard, and even the peculiar Japanese product with tail feathers sometimes as long as twenty feet.  That far-reaching changes can be brought about in a relatively short time is proved by the history of the game cock, which has nearly doubled in height since 1850, while at the same time its slender legs, long spurs, and other qualities have been perfected for the cruel sport for which it has been bred.  Again, the wild rock pigeon seems to be the ancestral form from which the fantail and pouter and carrier-pigeon with their diverse characters have taken their origin.

It is true that some biologists have urged certain technical objections to the employment of domesticated animals and their history as analogies to the processes and results in wild nature.  To my mind, however, artificial selection is truly a part of the whole process of natural selection.  Man is but one element of the environment of tame forms, and his fancy or need is therefore one of the varied series of external criteria that must be met if survival is to be the result; failing this, elimination follows as surely as under the conditions of an area uninhabited or uninfluenced by mankind.  Congenital variation is real, selection is real and the heredity of the more fit modification is equally real.  Surely Darwin was right in contending that the facts of this class amplify the conception of natural selection developed on the basis of an analysis of wild life.