A comparison of the skulls of the Tertiary mammals and those of our own day indicates that in certain of the important series, and presumably in them all, the brain has increased in size from the earlier to the later times. This increase in brain capacity has doubtless been attended by a decided gain in the measure of intelligence, a gain which has doubtless served to make the modern representatives of the series fitter for man's use than their ancestors were. For, while the number of our very useful domesticated forms may seem at first sight to be dull of wit, none of them are really low in the intellectual scale as we apply it to the brute; in fact, a considerable measure of intelligence is absolutely required as a condition for true subjugation. This is seen by the fact that nothing like a real adoption into our social system has ever been accomplished except with a few of the higher orders of mammals and birds, species which have an intellectual capacity that we recognize as akin to our own. Thus, so far as we can see, man's appearance on this stage was, so far as it relates to the possibility of companionship with the lower life, exceedingly well timed. He came at a period when the life was ready to give him and to receive from him a large measure of help. If his advent had been much earlier, he might have had less trouble in his contests with the larger carnivora; but if there had been a lack of beasts to obey his will, it is doubtful whether he could himself have won his way above that primitive life. DOMESTICATED BIRDS Domestication of Animals mainly accomplished by the Aryan Race; Small Amount of Such Work by American Indians.--Barnyard Fowl: Mental Qualities; Habits of Combat.--Peacocks: their Limited Domestication.--Turkeys: their Origin; tending to revert to the Savage State.--Water Fowl: Limited Number of Species domesticated; Intellectual Qualities of this Group.--The Pigeon: Origin and History of Group; Marvels of Breeding.--Song Birds.--Hawks and Hawking.--Sympathetic Motive of Birds: their AEsthetic Sense; their Capacity for Enjoyment. It is an interesting fact that about all the work of domestication which has been done by man has been accomplished by the peoples of Asia and mainly by the Aryan race. The American Indians tamed the llama and alpaca and a few species of native plants; even where their habits were prevailingly sedentary they domesticated no birds. It was left for Europeans to make use of the wild turkey. Our primitive people had the same chance to tame ducks and geese as the folk of the Old World. They appear, however, to have lacked all capacity for such endeavors. The same lack of disposition to capture and tame wild creatures is noticeable among the characteristic peoples of Africa; all of which serves to show that the domesticating art, at least as applied to animals, is peculiar to the higher-grade folk of the Old World.