Page:Popular Science Monthly Volume 72.djvu/79

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URING the last hundred years man has persistently and skilfully practised artificial selection on domestic animals. He has thus sometimes increased tenfold their value to him. Setting aside for reproduction those cows only which gave the greatest amount of milk, and those bulls, the mothers of which participated in the same characteristic, milk-making animals were evolved out of the former indifferent races of cows. The lean, hardy hog of the eighteenth century has been transformed into a wonderful machine for the quick making of fat. Selection practised for speed only has created races of horses which can for a short time compete with a locomotive.

While, in most cases of selection, man had in view the modification of certain physical characteristics, it can not be said that this was always his main purpose. The intellectual selection of animals has also been practised to some extent. Breeders of hunting dogs are as much concerned about what mothers and fathers thought and did in given circumstances as about their shape and color. The results of their work have been races the hunting propensities of which are quite as strong and not altogether unlike the blind impulse which prompts a New York clerk to spend one hundred dollars on hunting implements to get a few birds worth a few cents. The main difference between the hunting dog and the hunting clerk is that the former is mostly a recent product of artificial selection, while the latter is exclusively a result of paleolithic natural selection: at a time when agriculture was unknown, those families whose heads found no pleasure in hunting were slowly but steadily and surely eliminated by hunger and consequent diseases. The others remained.

And the most notable mental transformation undergone by dogs is not the developing of their hunting inclinations nor the creating of their doorkeeping and watching propensities. The dog is to-day the only animal which unmistakably loves his master, which expresses intense joy when shown some kindness or intense grief when told a harsh word. During the the long prehistoric ages, domestic dogs were treated as they are nowadays in savage tribes. Although each family kept a number of them, very little food was ever given them. Hunger killed every year many of them. Those which survived out of every generation were mostly those which had received from their masters some food in time of famine, and they were of course the most affectionate and demonstrative.