Their progress has been gradual. The greatness of nations, even when it seems to blaze forth in history most suddenly, ever finds its true origin in numerous steps of slow preparation. A hardy, frugal tribe of warriors is nursed in some obscure mountain cradle. The struggle for existence fosters their preservative virtues. A line of rulers is evoked, forced by the circumstances of their tenure to acquire, as their leading qualities, cunning, prudence, self-control, fertility of resource, promptitude of action, till at length the hour and the man coincide, and a handful of barbarians give their name to a great empire. The same rule prevails with languages, and the literatures that adorn them. So fully is this established in regard to literature, that men who examine the subject deeply are almost led to disbelieve in originality of genius altogether, from the invariable indebtedness of the noblest authors to the thoughts and imaginings of earlier minds. There is, therefore, no antecedent improbability that can fairly be pleaded against the gradual development of the human mind. On the contrary, every possible analogy is in its favour. A supposition so favoured becomes at least a lawful and reasonable subject of enquiry. If it be true that the theory of evolution applies to the mind of man, we should expect to find in that mind itself traces of the earlier steps, or grades of development, through which it has passed, and also in the world around creatures lower than humanity in some sort representing those earlier stages of slowly unfolding reason. In other words, we should expect to find in human nature itself those very inequalities, that very conflict of the higher and the lower elements on which moralists so urgently insist, and we should expect to find affinities and resemblances, more or less close, pervading the whole animal creation, and exhibiting human reason and brute intelligence as, upon a broad view, one in kind, however different in degree.