almost any other bird with which they are associated." Moreover, there are failures and imperfections in the nesting of birds that are not compatible with the theory of instinct, which is supposed to be infallible, but are quite so with the theory of intelligence and imitation. Furthermore, in their manner of building, birds adapt themselves to circumstances and frequently alter and improve. The theory of instincts in man is likewise in the wrong. The sucking of the child, which is said to be instinctive, is merely one of those _simple_ acts dependent on organization, like breathing or muscular motion. "So walking is evidently dependent on the arrangement of the bones and joints, and the pleasurable exertion of the muscles, which lead to the vertical posture becoming gradually the most agreeable one; and there can be little doubt that an infant would learn of itself to walk, even if suckled by a wild beast." The theory of instinct "implies innate ideas[25] of a very definite kind, and if established, would overthrow Mr. Mill's Sensationalism and all the modern philosophy of experience." The reason why natural selection acts so powerfully upon animals, is to be found mainly in their individual isolation. "A slight injury, a temporary illness, will often end in death, because it leaves the individual powerless against its enemies.... There is, as a rule, no mutual assistance between adults, which enables them to tide over a period of sickness. Neither is there any division of labor; each must fulfil _all_ the conditions of its existence, and therefore natural selection keeps all up to a pretty uniform standard." But in man as we now behold him, this is different. He is social and sympathetic; and in society, a division of labor takes place that leaves the physically defective still something to do by which he may sustain life, and saves him from the extreme penalty which falls upon animals so defective. By his skill in constructing for himself tools and clothing and in planting his own food, man has an immense advantage over the animals, in whom a change of structure must take place in adaptation to changed conditions. Moreover, he not only escapes natural selection himself, but "is actually able to take away some of that power from nature, which, before his appearance, she universally exercised," establishing so his supremacy by means of that subtle force we term mind. "We can anticipate the time when the earth will produce only cultivated plants and domestic animals, when man's selection shall have supplanted natural selection."