The foregoing considerations make it evident that the problem of domestication shades into the question as to the preservation of the life which is now on the earth, and this with a view to the advantage which the arts, the sciences, or general culture may obtain from the preservation of the useful, the instructive, and the beautiful things in the realm of nature from the swift destruction which our rude subjugation of the earth threatens to inflict. To deal with this problem in an adequate manner we must ask ourselves what limits are to be set to the displacement of the ancient order which is now going on. We see that wherever civilization enters, and even where its first influences are felt, the olden societies of nature are disturbed or broken up. All the nobler members of these associations, the greater mammals, many of the larger birds, and a host of the lesser forms, are expelled or destroyed. In the condition of organic life when the supremely predatory creature man rose to domination, the species were grouped in those vast organizations which were of old termed faunae and florae, but which are now better known as biological fields or provinces. In each of these hosts the several species were, as regards their external life, so balanced with their neighbors that the assemblage from the point of view of these relations might well be compared with the polities or states of man's construction. Such an organic society represents the result of a series of trials and balances which began to be made in the immeasurably remote past and have been continued through the geologic ages, each age adding something to the accord. The plants give and take from the animals; the insects are equated with the birds, and each species in every group has set up an accord with its rivals. From time to time the host has by the changes of sea and land been compelled to migrate, moving this way and that to find its fit station. In these movements species are rapidly extinguished, much as the weaker soldiers of an army perish in forced marches. Into their places new forms hasten to take their place, so that every position of advantage is filled. At a less rapid rate, but perpetually, even without the change of abode, which it is often by climatic changes compelled to make, the organic host is slowly changing in character; old kinds give way in the endless contest to new varieties which have managed to establish a better relation to the environment. Still the legions press on towards the great accomplishment of a higher and nobler life.