Nothing in human development is more impressive than the origin of the cerebrum and its development by passing through successive stages which are counterparts in the main of the adult brains of other and lower animals. The alteration of a tissue-mechanism constructed in one way into a tissue-mechanism of a more complex nature, provides the most conclusive evidence of the reality of brain evolution, because the process of transformation actually takes place.
But in the present connection we are more interested in the dynamic or functional aspects of mental evolution, which it must be remembered are inseparably bound up with the physical structures and their modifications. After a human infant is born its activities are reflex and mechanical like those of the adult members of lower groups. As it grows it performs instinctive acts because its inherited nervous system operates in the purely mechanical manner of a lower mammal's nervous system. For these reasons an eminent psychologist has said that the mental ability of an infant six months old is about that of a well-bred fox terrier. The same infant at nine months displays an intelligence of a higher order equal to that of a well-trained chimpanzee; it has become what it was not, and in so far it has truly evolved in mental respects. At two years of age the child is incapable of solving problems of the calculus, for its reasoning powers are elementary and restricted, but these same powers change and intensify so as to render the older mind quite capable of grasping the highest of human conceptions and ideas. In my judgment the unbroken transformation of a child's mind that exhibits only instinct and intelligence into an adult's mind with its power of reasoning, is far more conclusive as proof of mental evolution than the inference drawn from the comparisons we have made above of the adult psychological phenomena of man, ape, cat, and fish. It is surely natural for such mental transformations to take place, for they do take place in the vast majority of human beings; when they do not, in cases where the brain fails to mature, we speak of unnatural or diseased minds.
The third division of our evidence relating to mental evolution constitutes what we have called the palæontology of mind. By this term we mean the study of human minds of the past as we may know them through the many varied relics and documents which indicate their characters. It is only too obvious to every one that human knowledge has advanced in the course of time and that every department of human thought and mental activity has participated in this progress. No one would have the temerity to assert that we know nothing more than our ancestors of 5000 or even 1000 years ago. Our common-sense teaches us even before the man of science produces the full body of evidence at his disposal that human faculties have evolved. With regard to reasoning powers, which form one of the four distinguishing characteristics of the human species as contrasted with other animals, the case has already been reviewed, and we now turn to speech and language and other departments of human mentality. When we compare the attainments of present day men with the abilities and ideas of their ancestors we will do for mental phenomena precisely what was done when we compared the skeletons of modern animals with those of creatures belonging to bygone geological ages; in this reason is found the justification for the phrase employed in the present connection.
Written history furnishes a wealth of material for interpreting the mental conditions of ancient peoples, but beside documentary evidence the anthropologist learns to use inscriptions of prehistoric times, the primitive graphic representations on tombs and monuments, and even the characteristics of crude implements like axes and arrow-heads. The layman finds it difficult at first to regard such relics as indications of the mental stature of the people who made and possessed them; but a little thought will show that a man who used a rough stone ax in the time of the ancient Celts could not possibly have had a mind which included the conception of a finished iron tool or modern mechanism. So in all departments of human culture, the evolution of material objects may be justly employed in interpreting and estimating the mental abilities of ancient peoples.
Language is undoubtedly the most important single intellectual possession of mankind, for it constitutes, as it were, the very framework of social organization. Without a ready means of communication the myriad human units who perform the varied tasks necessary for the economic well-being of a body-politic would be unable to coordinate their manifold activities with success, and the structure of civilized societies at least would collapse. It needs no legend of a Tower of Babel to make this plain. So fundamental is this truth that although we may not have recognized it explicitly, we unconsciously form the belief that speech and language are exclusive properties of the human species, and even more characteristic of man alone than the power of reason itself. While organized language is clearly something that as such we do not share with the lower animals, nevertheless we cannot regard the communication of ideas or states of feeling by sound as an exclusive property of mankind. All are familiar with the difference between the whine and the bark of a dog and with the widely different feelings that are expressed by these contrasted sounds. And we know too that dogs can understand what many of their master's words signify, as when a shepherd gives directions to his collie. We could even go further down in the scale and find in the shrill chirping of the katydid at the mating season a still more elementary combination of significant instinctive sound elements. To the comparative student the speech of man differs from these lower modes of communication only in its greater complexity, and in its employment of more numerous and varied sounds,—in a word, only in the higher degree of its evolution. And it is even more evident that the diverse forms of speech employed by various races have gradually grown to be what they now are.
At the outset it is well to distinguish between writing, as the conventional mode of symbolizing words, and spoken language itself; the two have been more independent in their evolution than we may be wont to believe. Speech came first in historical development, just as a child now learns to talk before it can understand and use printed or written letters. Furthermore, many races still exist who have a well-developed form of language without any concrete way of recording it. It is true, of course, that back of the conventions of speech and writing are the ideas themselves that find expression in the one way or the other, or even by the still more primitive use of signs and gestures. But it is not with these ultimate elements of thought that we are now concerned; our task is to learn, first, what evidences are discoverable which show that the property of human language in general has originated by evolution, and then, in the second place, to perceive how this development proves an evolution of one group of ultimate ideas, namely, human concepts of the modal value of words and symbols as expressions of ideas themselves.
A simple common-sense treatment of obvious facts will greatly facilitate our progress. We know very well that the English we speak to-day differs in many ways from the language of Elizabethan times, and that the former is a direct descendant of the other. The latter, in turn, was a product of Norman French and Anglo-Saxon,—a combination of certain elements of both, but identical with neither of its immediate parents. The Saxon tongue itself has a history that leads back to King Alfred's time and earlier. Thus we are already aware of the fact that our speech has truly evolved, like the physical structure of the men who employ it; and we know, too, how readily new words are adopted into current English, like tabu from Polynesia, or garage from the French, showing that language is even now in process of evolution.
The sounds that make up spoken words can be resolved into a single element with its modifications; this basic element is the brute-like call or shout made with the mouth and throat opened wide—a sound we may have heard uttered by men under the stress of pain or terror. All of the various vowels are simply modifications of this element by altering the shape of the mouth cavity and orifice, while the consonants are produced by interrupting the sound-waves with the palate or lips or tongue. Like the cell as a unit of structure throughout the organic world, this elemental utterance proves to be the basic unit of all human languages, which vary so widely among races of to-day no less than they have in the history of any single people.
One of the first steps in the making of spoken words was taken by human beings when they imitated the calls or other sounds produced by living things, and tacitly agreed to recognize the imitation as a symbol of the creature making it. Thus the names for the cuckoo and the crow in many languages besides our own are simply copies of the calls uttered by these birds; a Tahitian calls a cat mimi; the name for a snake almost invariably includes the hissing attributed to that creature. After a time words which were at first simply imitations and which referred only to the things that made these sounds came to refer to certain qualities of the things imitated, so that the naming of other than natural objects, such as qualities, began, leading ultimately to the use of words for qualities belonging to many and different objects in the way of abstractions.
Much light upon the evolution of language is obtained when we treat the speech of various races as we did the skeletal structures of cats and seals and whales. When we compare the Italian, Spanish, Portuguese, and French languages, they reveal the same general structure in thousands of their words,—a common basis which in these cases is due to their derivation from the same ancestor, the Latin tongue. The Latin word for star is stella, and the Italian word of to-day is an identical and unchanged descendant, like a persistent type of shark which lives now in practically the same form as did its ancestor in the coal ages. The Spanish word is estrella, a modified derivative, but still one that bears in its structure the marks of its Latin origin; the French word étoile is a still more altered product of word evolution. Even in the German stern, Norse stjern, Danish starn, and English star we may recognize mutual affinities and common ancestral structure. Choosing illustrations from a different group, the Hebrew salutation "Peace be with you," Shalom lachem, proves to be a blood cousin of the Arabic Salaam alaikum, indicating the common ancestry of these diverse languages. Among Polynesian peoples the Tahitian calls a house a fare, the Maori of New Zealand uses whare, while the Hawaiian employs the word hale, and the Samoan, fale. Whenever we classify and compare human languages, we find similar consistent anatomical evidences of their relationships and evolution. We can even discern counterparts of the vestigial structures like the rudimentary limbs of whales. In the English word night certain letters do not function vocally, though in the German counterpart Nacht their correspondents still play a part. In the word dough as correctly pronounced the final letters are similarly vestigial, although in the phonetic relative tough they are still sounded.