In the foregoing ontogenetic mirror will be found the key to the unfolding of the great mystery of the evolution of mind in the animal kingdom. We have only to take the geological periods one after the other, and study the various life-forms found in each to see at once that, with the race, the order of sequence in the appearance of the intellectual and emotional faculties is precisely the same as with the individual. We may place the new-born infant intellectually on a par with the lowly molluscs or the vermiform little animals which existed in the Cambrian period, in which little organisms probably pain first made its entry upon the earth, followed by the appearance of pleasure, memory (conscious), and association of ideas in the lowly crustaceans of the later Cambrian and early Silurian periods. With the spiders, fishes, and crabs of the later Silurian and Devonian periods we have brought before us the faculty of recognising places of which these animals are capable, which places them intellectually on a level with a child of four or five months old.
The recognition of individuals next made its appearance in the reptiles of the Carboniferous and Permian epochs; while the birds of the Oölitic and Cretaceous periods were the first to dream, and are thus placed on an intellectual level with a child of five or six months. The emotional development coincides with the intellectual, just as in the case of the infant, for we find fear manifesting itself among the lower molluscs, pugnacity among the crustaceans, play among spiders and crabs, anger among reptiles, and emulation, jealousy, joy, and grief among birds. We now rise in the palæontological scale to the Tertiary period, and find in the Eocene age equine and other mammal forms, such as cats and pigs, which are capable of understanding words and signs, and among which we notice a manifestation of sympathy, curiosity, revenge, and gratitude. In the early Meiocene age we have monkeys, dogs, and elephants exhibiting the clearest signs of true reason, as may be observed at the present day, and at the same time manifesting such emotional signs as pride, shame, deceitfulness, passionateness, cruelty, and ludicrousness, which places them on an intellectual par with the infant of less than a year old.
In the later Meiocene age we have anthropoid apes, which may be placed on a level with one-year-old infants, and from which evolved apes of a higher order, which acquired the faculty of articulation, and, afterwards becoming more human, the knowledge of the use of simple instruments, thus reaching the intellectual level of the child of fifteen months old. As the apes became more and more human in the later Meiocene and early Pleistocene ages, they gradually acquired the faculty of acting in concert and of speech; and when, having arrived at that stage of development in which they partook more of the character of savage man than human ape, judgment, recollection, self-consciousness, and, lastly, definite morality manifested themselves, thus raising the ape-like man to the level of the child of two and a half years. In the lowest savages of to-day, as well as in the old descendants of the ape-like men, superstition developed to a large extent at the same time that the emotional unfolding proceeded in the direction of avarice, envy, hate, hope, vanity, mirth, a love of the beautiful, and afterwards art appreciation, awe, reverence, remorse, courtesy, melancholy, and ecstasy, precisely as with the child of from five to ten years of age. As the race improved, becoming in turn semi-savage, semi-civilised, civilised, and cultured, the intellectual powers, of course, developed similarly, until, at the present day, we find men possessed of the most wonderful mental grandeur, we might almost say, conceivable. But this would be saying too much, for we must not forget that, just as evolution has continued in the past from eternity, so will it continue in the future to eternity; and who can tell to what heights the human mind may soar in the future?
Lofty as is the human intellect at the present time, as compared with the mental powers of those we have left far behind in the march of evolution, it is yet very far from being able to grasp many of the great problems of the universe, such as that of existence. Perhaps at some future time, in millions of ages to come, these great questions may be answered; but at present we know they baffle the wisest men, and continually remind us of the finite and limited character of our intellectual faculties.
This comparison of the mental development of the individual with that of the whole race is extremely interesting, and provides ample material for thought. By such comparison, and by it alone, can the science of psychology ever be based on a sure and enduring foundation. It is all very well for theologians and other biased people to declare that animal intelligence has nothing in common with the reasoning powers of man; but let them honestly look at the facts as they are, thanks to the indefatigable energy and indomitable perseverance of lovers of science and truth, now presented to us. Candid observers cannot fail to notice that the difference between the intelligence of man and that of the lower animals is one only of degree, and not of kind. When we see the order of sequence being followed in the development of the individual so like that of the whole race, not only as regards the bodily structure, but also as regards the mental functions, can we help arriving at the conclusion that the one is but the epitome of the other, and that the superior intellect of man is but a higher development of the so-called instincts of the lower animals? Have we not at the present day, among members of the human family itself, various degrees of intelligence, from the almost barren brains of the lowest races of savages to the brilliant mental achievements of a Newton or a Spencer?
It is beyond doubt that the intellectual superiority of civilised man over his savage brethren is due to the greater multiplicity of his objects of thought, and it follows that savage man’s intellectual superiority over the lower animals is due to the same cause. The actions of both have the same aim—viz., the supplying of the wants of the physical nature and the gratifying of the desires aroused in the mind. It is frequently asserted that man differs from the lower animals in possessing the power of reflection; but this I hold to be an exploded argument, and at variance with all recent teaching. Dogs, elephants, and monkeys most certainly possess the faculty of reflection, and it is not difficult to find races belonging to the human family whose powers of reflection transcend hardly in the least degree those possessed by the higher apes; while the difference between the reflective capacity of the lowest savage, which is of the simplest conceivable kind, and that of the civilised European, which has developed into genius, is enormous. Then, again, it is often said that only man is emotional; but one need only have an ordinary acquaintanceship with domestic animals to at once see the absurdity of this argument, for dogs are frequently observed to laugh, to cry, to express joy and gratitude by their actions, and to betray feelings of shame and remorse; while horses and elephants have been observed to punish their cruel keepers in the most cunning manner and then to laugh at the poor fellows’ discomfiture. As to the “conscience argument,” so frequently brought forward, by religionists especially, all I have to say here is that conscience, or the knowledge of the distinction between right and wrong, is not an inherent quality of the human mind, being merely a result of the operation of the reflective faculty aided by experience, as is quite evident from the fact that the ideas of morality vary according to the age in which we live. The same may be said about the greatest of all the arguments against evolution—viz., that of language; for, just as conscience is but a product of reflection and experience, so is language also. It is a mistake to imagine that the power of speech is possessed by man alone, and that his language differs altogether from the cries and signals of the lower animals, for such is not the case. Many animals possess the faculty of speech, and human language differs from that of the lower animals only in its degree of development, and in no sense in its origin. Probably all language originated in interjection, or the “instinctive expression of the subjective impressions derived from external nature,” as Mr. Farrar puts it. And, just as the reflective powers of the race were developed and shone more brilliantly as each stage in the evolutionary march of intellect was passed, so did language pass from the simple monosyllabic cries to the complex dialects of modern civilisation; and it is worthy of notice that, at the present day, or at any rate very recently, there were races of savage men inhabiting this earth who possessed no language at all, and could not, on account of their mode of living, be placed on a higher intellectual level than the higher apes; while we have the authority of the leading philologists of the times in support of the fact that the monosyllabic cries of some of the lower human tribes are quite within the grasp of the ape’s voice.
Human beings have been discovered in wild and hitherto unexplored regions who have not the remotest idea of what we should term civilisation. They lead a wandering and useless life, sleeping at nights, not in huts, nor in caves, but squatting among the branches of tall trees, where they are placed out of the reach of savage animals. They do not appear capable of expressing their thoughts in sentences, but make use of exclamatory grunts, which serve the purposes of speech quite sufficiently for their limited requirements; and their general appearance approaches to a remarkable extent that of the higher apes, in that they are almost completely covered with hair, possess a dirty brown skin, short legs, long arms, and full abdomens, can pick up stones, sticks, etc., with their toes as well as their fingers, and show few if any signs of intellectual powers. Let any one visit the Zoological Gardens, in London, and carefully observe the apes exhibited there, and then say whether there is a vast difference between some of them and the human beings who answer to the above description. One need but visit the travelling menagerie of Messrs. Edmunds, and view their “missing link,” an excellent sample of the chimpanzee troglodyte, to see that the difference between man and the lower animals is one only of degree, quite as much as regards intellect as bodily form. I once saw exhibited in the Jardin d’Acclimatation, in Paris, a lot of Patagonian or Fuegan (I forget which) natives, who were very little superior intellectually to the chimpanzee. They were stark naked, in a wretchedly dirty condition, and appeared quite incapable of anything like sustained mental effort. But these are by no means the lowest among the human species.
In conclusion, I need only re-state my opinion that all so-called living things are but products of the development of protoplasm, whether belonging to the animal or vegetable kingdoms; that this protoplasm possesses the property of vitality, or the power of perceiving stimuli of various kinds and responding to them by definite movements; that the phenomena of mind are but functional manifestations of this protoplasmic development; and that the highest intellectual product of the human mind exists and has existed from eternity in a state of latent potentiality in every atom of protoplasm, as well as in every particle of matter in the universe.