The power of adaptation to varieties in external condition, which renders Man to a great extent independent of them, is one of the most remarkable peculiarities of his economy. He is capable of sustaining the lowest as well as the highest extremes of temperature and of atmospheric pressure. In the former of these particulars he is strikingly contrasted with the anthropoid apes ; the Chimpanzee being restricted to the hottest parts of Africa, and the Orang outan to the tropical portions of the Indian Archipelago'; and neither of these animals being capable of living in temperate climates without the assistance of artificial heat, even with the aid of which they have not hitherto survived their second dentition. So, again, although Man's diet seems naturally of a mixed character, he can support himself in health and strength either on an exclusively vegetable diet, or, under particular circumstances, on an almost exclusively animal diet. It is in thus adapt ing himself to the conditions of his existence, in providing himself with food, shelter, wea pons of attack and defence, &c., that man's intellectual powers are first called into active operation ; and when thus aroused, their development has no assignable limit. The will, guided by the intelligence, and acted on by the desires and emotions, takes the place in man of the instinctive propensities which are the usual springs of action in the lower animals ; and although, among the most ele vated of these, the intelligent will is called into exercise to a certain extent, yet it never acquires among them, the dominance which it possesses in man. The capacity for intel lectual progress is a remarkable peculiarity of man's psychical nature. The instinctive habits of the lower animals are limited, and peculiar to each species, and have immediate reference to their bodily wants. Where a particular adaptation of means to ends, of actions to circumstances, is made by an indi vidual (as is frequently the case, when some amount of intelligence or rationality exists), the rest do not seem to profit by it ; so that, although (as will be shown hereafter) the in stincts of particular animals may be modified by the training of man, or by the education of circumstances, so as to show themselves after a few generations under new forms, no elevation in intelligence appears ever to take place spontaneously, no psychical im provement is manifested in the species at large. One of the most important aids in the use and development of the human mind, is the capacity for articulate speech ; of which, so far as we know, man is the only animal in possession. There is no doubt that many other species have certain powers of com munication between individuals; but these are probably very limited, and of a kind more allied to the " language of signs," than to a proper verbal language. In fact it is obvious that the use of a language composed of a cer certain number of distinct sounds, combined into words in a multitude of different modes, requires a certain degree of that power of abstraction and generalisation, in which (as elsewhere remarked*) it appears that the lower animals are altogether deficient. The correspondence between the psychical endow ments of the Chimpanzee and those of the Human infant before it begins to speak, is extremely close ; and those who have perused the interesting narrative given by Dr. Howe,
of his successful training of Laura Bridgeman, will remember how marked was the improve ment in her mental condition, from the time when she first apprehended the idea that she could give such expression to her thoughts, feelings and desires, as should secure their being comprehended by others.
Now, this capacity for progress is con nected with another element in Man's nature, which it is difficult to isolate and define, but which interpenetrates and blends with his whole psychical character. " The soul," it has been remarked, "is that side of our nature which is in relation with the infinite ;" and it is the existence of this relation, in whatever way we may describe it, which seems to con stitute the most distinctive peculiarity of man. It is in the desire 'for an improvement in his condition, occasioned by an aspiration after something nobler and purer, that the main spring of human progress may be said to lie; among the lowest races of mankind, the capa city exists, but the desire seems dormant. When once thoroughly awakened, however, it seems to " grow by what it feeds on ;" and the advance once commenced, little external stimulus is needed ; for the desire increases at least as fast as the capacity. In the higher grades of mental development, there is a con tinual looking upwards, not (as in the lower) towards a more elevated human standard, but at once to something beyond and above man and material nature. This seems the chief source of the tendency to believe in some unseen existence ; which may take various forms, but seems never entirely absent from any race or nation, although, like other innate tendencies, it may be deficient in individuals. Attempts have been made by some travellers to prove that particular nations are destitute of it ; but such assertions have been based only upon a limited acquaintance with their habits of thought, and with their outward observances ; for there are probably none who do not possess the idea of some invisible power, external to themselves, whose favour they seek, and whose anger they deprecate, by sacrifice and other ceremonials. It re quires a higher mental cultivation than is commonly met with, to conceive of this power as having a spiritual existence ; but wherever the idea of spirituality can be de fined, it seems connected with it. The vulgar readiness to believe in demons, ghosts, &c. is only an irregular or depraved manifestation of the same tendency. Closely connected with it, is the desire to participate in this spiritual existence, which has been implanted in the mind of man, and which, developed as it is by the mental cultivation that is almost necessary for the formation of the idea, has been regarded by philosophers in all ages as one of the chief natural arguments for the immortality of the soul. By this immortal soul, Man is connected with that higher order of being, in which Intelligence exists, un restrained in its exercise by the imperfections of that corporeal mechanism through which it here operates ; and to this state, — a state of more intimate communion of mind with mind, and of creatures with their Creator,— he is encouraged to aspire, as the reward of his improvement of the talents here committed to his charge.