Anthropology

7. The “Missing Link”

No modern zoölogist has the least doubt as to the general fact of organic evolution. Consequently anthropologists take as their starting point the belief in the derivation of man from some other animal form. There is also no question as to where in a general way man’s ancestry is to be sought. He is a mammal closely allied to the other mammals, and therefore has sprung from some mammalian type. His origin can be specified even more accurately. The mammals fall into a number of fairly distinct groups, such as the Carnivores or flesh-eating animals, the Ungulates or hoofed animals, the Rodents or gnawing animals, the Cetaceans or whales, and several others. The highest of these mammalian groups, as usually reckoned, is the Primate or “first” order of the animal kingdom. This Primate group includes the various monkeys and apes and man. The ancestors of the human race are therefore to be sought somewhere in the order of Primates, past or present.

The popular but inaccurate expression of this scientific conviction is that “man is descended from the monkeys,” but that a link has been lost in the chain of descent: the famous “missing link.” In a loose way this statement reflects modern scientific opinion; but it certainly is partly erroneous. Probably not a single authority maintains to-day that man is descended from any species of monkey now living. What students during the past sixty years have more and more come to be convinced of, was already foreshadowed by Darwin: namely that man and the apes are both descended from a common ancestor. This common ancestor may be described as a primitive Primate, who differed in a good many details both from the monkeys and from man, and who has probably long since become extinct.

The situation may be clarified by two diagrams (Fig. 1). The first diagram represents the inaccurate view which puts the monkey at the bottom of the line of descent, man at the top, and the missing link in the middle of the straight line. The illogicality of believing that our origin occurred in this manner is apparent as soon as one reflects that according to this scheme the monkey at the beginning and man at the end of the line still survive, whereas the “missing link,” which is supposed to have connected them, has become extinct.

Clearly the relation must be different. Whatever the missing link may have been, the mere fact that he is not now alive on earth means that we must construct our diagram so that it will indicate his past existence as compared with the survival of man and the apes. This means that the missing link must be put lower in the figure than man and the apes, and our illustration therefore takes on the form shown in the right half of figure 1, which may be described as Y-shaped. The stem of the Y denotes the pre-ancestral forms leading back into other mammalian groups and through them—if carried far enough down—to the amphibians and invertebrates. The missing link comes at the fork of the Y. He represents the last point at which man and the monkeys were still one, and beyond which they separated and became different. It is just because the missing link represented the last common form that he was the link between man and the monkeys. From him onwards, the monkeys followed their own course, as indicated by the left-hand branch of the Y, and man went his separate way along the right-hand branch.

8. Family Tree of the Primates

While this second diagram illustrates the most essential elements in modern belief as to man’s origin, it does not of course pretend to give the details. To make the diagram at all precise, the left fork of the Y, which here stands for the monkeys as a group—in other words, represents all the living Primates other than man—would have to be denoted by a number of branching and subdividing lines. Each of the main branches would represent one of the four or five subdivisions or “families” of the Primates, such as the Anthropoid or manlike apes, and the Cebidæ or South American monkeys. The finer branches would stand for the several genera and species in each of these families. For instance, the Anthropoid line would split into four, standing respectively for the Gibbon, Orang-utan, Chimpanzee, and Gorilla.

The fork of the Y representing man would not branch and rebranch so intricately as the fork representing the monkeys. Many zoölogists regard all the living varieties of man as constituting a single species, while even those who are inclined to recognize several species limit the number of these species to three or four. Then too the known extinct varieties of man are comparatively few. There is some doubt whether these human fossil types are to be reckoned as direct ancestors of modern man, and therefore as mere points in the main human line of our diagram; or whether they are to be considered as having been ancient collateral relatives who split off from the main line of human development. In the latter event, their designation in the diagram would have to be by shorter lines branching out of the human fork of the Y.

This subject quickly becomes a technical problem requiring rather refined evidence to answer. In general, prevailing opinion looks upon the later fossil ancestors of man as probably direct or true ancestors, but tends to regard the earlier of these extinct forms as more likely to have been collateral ones. This verdict applies with particular force to the earliest of all, the very one which comes nearest to fulfilling the popular idea of the missing link: the so-called Pithecanthropus erectus. If the Pithecanthropus were truly the missing link, he would have to be put at the exact crotch of the Y. Since he is recognized, however, as a form more or less ancestral to man, and somewhat less ancestral to the apes, he should probably be placed a short distance up on the human stem of the Y, or close alongside it. On the other hand, inasmuch as most palæontologists and comparative anatomists believe that Pithecanthropus was not directly ancestral to us, in the sense that no living men have Pithecanthropus blood flowing in their veins, he would therefore be an ancient collateral relative of humanity—a sort of great-great-granduncle—and would be best represented by a short stub coming out of the human line a little above its beginning (Fig. 2).

Even this figure is not complete, since it is possible that some of the fossil types which succeeded Pithecanthropus in point of time, such as the Heidelberg and Piltdown men, were also collateral rather than direct ancestors. Some place even the later Neandertal man in the collateral class. It is only when the last of the fossil types, the Cro-Magnon race, is reached, that opinion becomes comparatively unanimous that this is a form directly ancestral to us. For accuracy, therefore, figure 2 might be revised by the addition of other short lines to represent the several earlier fossil types: these would successively spring from the main human line at higher and higher levels.

In order not to complicate unnecessarily the fundamental facts of the case—especially since many data are still interpreted somewhat variously—no attempt will be made here to construct such a complete diagram as authoritative. Instead, there are added reproductions of the family tree of man and the apes as the lineages have been worked out independently by two authorities (Figs. 3, 4). It is clear that these two family trees are in substantial accord as regards their main conclusions, but that they show some variability in details. This condition reflects the present state of knowledge. All experts are in accord as to certain basic principles; but it is impossible to find two authors who agree exactly in their understanding of the less important data.

9. Geological and Glacial Time

A remark should be made here as to the age of these ancestral forms. The record of life on earth, as known from the fossils in stratified rocks, is divided into four great periods. The earliest, the Primary or Palæozoic, comprises about two-thirds of the total lapse of geologic time. During the Palæozoic all the principal divisions of invertebrate animals came into existence, but of the vertebrates only the fishes. In the Secondary or Mesozoic period, evolution progressed to the point where reptiles were the highest and dominant type, and the first feeble bird and mammal forms appeared. The Mesozoic embraces most of the remaining third or so of the duration of life on the earth, leaving only something like five million years for the last two periods combined, as against thirty, fifty, ninety, or four hundred million years that the Palæozoic and Mesozoic are variously estimated to have lasted.

These last five million years or so of the earth’s history are divided unequally between the Tertiary or Age of Mammals, and the Quaternary or Age of Man. About four million years are usually assigned to the Tertiary with its subdivisions, the Eocene, Oligocene, Miocene, and Pliocene. The Quaternary was formerly reckoned by geologists to have lasted only about a hundred thousand years. Later this estimate was raised to four or five hundred thousand, and at present the prevailing opinion tends to put it at about a million years. There are to be recognized, then, a four million year Age of Mammals before man, or even any definitely pre-human form, had appeared; and a final period of about a million years during which man gradually assumed his present bodily and mental type. In this Quaternary period fall all the forms which are treated in the following pages.

The Quaternary is usually subdivided into two periods, the Pleistocene and the Recent. The Recent is very short, perhaps not more than ten thousand years. It represents, geologically speaking, the mere instant which has elapsed since the final disappearance of the great glaciers. It is but little longer than historic time; and throughout the Recent there are encountered only modern forms of man. Back of it, the much longer Pleistocene is often described as the Ice Age or Glacial Epoch; and both in Europe and North America careful research has succeeded in demonstrating four successive periods of increase of the ice. In Europe these are generally known as the Günz, Mindel, Riss, and Würm glaciations. The probable American equivalents are the Nebraskan, Kansan, Illinoian, and Wisconsin periods of ice spread. Between each of these four came a warmer period when the ice melted and its sheets receded. These are the “interglacial periods” and are designated as the first, second, and third. These glacial and interglacial periods are of importance because they offer a natural chronology or time scale for the Pleistocene, and usually provide the best means of dating the fossil human types that have been or may hereafter be discovered (Fig. 5).

10. Place of Man’s Origin and Development

Before we proceed to the fossil finds themselves, we must note that the greater part of the surface of the earth has been very imperfectly explored. Africa, Asia, and Australia may quite conceivably contain untold scientific treasures which have not yet been excavated. One cannot assert that they are lying in the soil or rocks of these continents; but one also cannot affirm that they are not there. North and South America have been somewhat more carefully examined, at least in certain of their areas, but with such regularly negative results that the prevailing opinion now is that these two continents—possibly through being shut off by oceans or ice masses from the eastern hemisphere—were not inhabited by man during the Pleistocene. The origin of the human species cannot then be sought in the western hemisphere. This substantially leaves Europe as the one continent in which excavations have been carried on with prospects of success; and it is in the more thoroughly explored western half of Europe that all but two of the unquestioned discoveries of ancient man have been made. One of these exceptional finds is from Africa. The other happens to be the one that dates earliest of all—the same Pithecanthropus already mentioned as being the closest known approach to the “missing link.” Pithecanthropus was found in Java.

Now it might conceivably prove true that man originated in Europe and that this is the reason that the discoveries of his most ancient remains have to date been so largely confined to that continent. On the other hand, it does seem much more reasonable to believe that this smallest of the continents, with its temperate or cold climate, and its poverty of ancient and modern species of monkeys, is likely not to have been the true home, or at any rate not the only home, of the human family. The safest statement of the case would be that it is not known in what part of the earth man originated; that next to nothing is known of the history of his development on most of the continents; and that that portion of his history which chiefly is known is the fragment which happened to take place in Europe.

11. Pithecanthropus

Pithecanthropus erectus, the “erect ape-man,” was determined from the top part of a skull, a thigh bone, and two molar teeth found in 1891 under fifty feet of strata by Dubois, a Dutch surgeon, near Trinil, in the East Indian island of Java. The skull and the thigh lay some distance apart but at the same level and probably are from the same individual. The period of the stratum is generally considered early Pleistocene, possibly approximately contemporary with the first or Günz glaciation of Europe—nearly a million years ago, by the time scale here followed. Java was then a part of the mainland of Asia.

The skull is low, with narrow receding forehead and heavy ridges of bone above the eye sockets—“supraorbital ridges.” The capacity is estimated at 850 or 900 cubic centimeters—half as much again as that of a large gorilla, but nearly one-half less than the average for modern man. The skull is dolichocephalic—long for its breadth—like the skulls of all early fossil men; whereas the anthropoid apes are more broad-headed. The jaws are believed to have projected almost like a snout; but as they remain undiscovered, this part of the reconstruction is conjectural. The thigh bone is remarkably straight, indicating habitual upright posture; its length suggests that the total body stature was about 5 feet 7 inches, or as much as the height of most Europeans.

Pithecanthropus was a terrestrial and not an arboreal form. He seems to have been slightly more similar to modern man than to any ape, and is the most primitive manlike type yet discovered. But he is very different from both man and the apes, as his name indicates: Pithecanthropus is a distinct genus, not included in Homo, or man.

12. Heidelberg Man

Knowledge of Heidelberg man rests on a single piece of bone—a lower jaw found in 1907 by Schoetensack at a depth of nearly eighty feet in the Mauer sands not far from Heidelberg, Germany. Like the Pithecanthropus remains, the Heidelberg specimen lay in association with fossils of extinct mammals, a fact which makes possible its dating. It probably belongs to the second interglacial period, so that its antiquity is only about half as great as that of Pithecanthropus (Fig. 5).

The jaw is larger and heavier than any modern human jaw. The ramus, or upright part toward the socket, is enormously broad, as in the anthropoid apes. The chin is completely lacking; but this area does not recede so much as in the apes. Heidelberg man’s mouth region must have projected considerably more than that of modern man, but much less than that of a gorilla or a chimpanzee. The contour of the jaw as seen from above is human (oval), not simian (narrow and oblong).

The teeth, although large, are essentially human. They are set close together, with their tops flush, as in man; the canines lack the tusk-like character which they retain in the apes.

Since the skull and the limb bones of this form are wholly unknown, it is somewhat difficult to picture the type as it appeared in life. But the jaw being as manlike as it is apelike, and the teeth distinctly human, the Heidelberg type is to be regarded as very much nearer to modern man than to the ape, or as farther along the line of evolutionary development than Pithecanthropus; as might be expected from its greater recency. This relationship is expressed by the name, Homo Heidelbergensis, which recognizes the type as belonging to the genus man.

13. The Piltdown Form

This form is reconstructed from several fragments of a female brain case, some small portions of the face, nearly half the lower jaw, and a number of teeth, found in 1911-13 by Dawson and Woodward in a gravel layer at Piltdown in Sussex, England. Great importance has been ascribed to this skull, but too many of its features remain uncertain to render it safe to build large conclusions upon the discovery. The age cannot be fixed with positiveness; the deposit is only a few feet below the surface, and in the open; the associated fossils have been washed or rolled into the layer; some of them are certainly much older than the skull, belonging to animals characteristic of the Pliocene, that is, the Tertiary. If the age of the skull was the third interglacial period, as on the whole seems most likely, its antiquity might be less than a fourth that of Pithecanthropus and half that of Heidelberg man.

The skull capacity has been variously estimated at 1,170, nearly 1,300, and nearly 1,500 c.c.; the pieces do not join, so that no certain proof can be given for any figure. Except for unusual thickness of the bone, the skull is not particularly primitive. The jaw and the teeth, on the other hand, are scarcely distinguishable from those of a chimpanzee. They are certainly far less human than the Heidelberg jaw and teeth, which are presumably earlier. This human skull and simian jaw are an almost incompatible combination. More than one expert has got over the difficulty by assuming that the skull of a contemporary human being and the jaw of a chimpanzee happened to be deposited in the same gravel.

In view of these doubts and discrepancies, the claim that the Piltdown form belongs to a genus Eoanthropus distinct from that of man is to be viewed with reserve. This interpretation would make the Piltdown type more primitive than the probably antecedent Heidelberg man. Some authorities do regard it as both more primitive and earlier.

14. Neandertal Man

The preceding forms are each known only from partial fragments of the bones of a single individual. The Neandertal race is substantiated by some dozens of different finds, including half a dozen nearly complete skulls, and several skeletons of which the greater portions have been preserved. These fossils come from Spain, France, Belgium, Germany, and what was Austro-Hungary, or, roughly, from the whole western half of Europe. They are all of similar type and from the Mousterian period of the Palæolithic or Old Stone Age (§ 70-72, Fig. 17); whereas Pithecanthropus, Heidelberg, and perhaps Piltdown are earlier than the Stone Age. The Mousterian period may be dated as coincident with the peak of the last or Würm glaciation, that is, about 50,000 to 25,000 years ago. Its race—the Neandertal type—was clearly though primitively human; which fact is reflected in the various systematic names that have been given it: Homo Neandertalensis, Homo Mousteriensis, or Homo primigenius.

The Most Important Neandertal Discoveries

Neandertal man was short: around 5 feet 3 inches for men, 4 feet 10 inches for women, or about the same as the modern Japanese. A definite curvature of his thigh bone indicates a knee habitually somewhat bent, and probably a slightly stooping or slouching attitude. All his bones are thickset: his musculature must have been powerful. The chest was large, the neck bull-like, the head hung forward upon it. This head was massive: its capacity averaged around 1,550 c.c., or equal to that of European whites and greater than the mean of all living races of mankind (Fig. 6). The head was rather low and the forehead sloped back. The supraorbital ridges were heavy: the eyes peered out from under beetling brows. The jaws were prognathous, though not more than in many Australians and Negroes; the chin receded but existed.

Some Neandertal Measurements

The artifacts found in Mousterian deposits show that Neandertal man chipped flint tools in several ways, knew fire, and buried his dead. It may be assumed as almost certain that he spoke some sort of language.

15. Rhodesian Man

Quite recent is the discovery of an African fossil man. This occurred in 1921 at Broken Hill Bone Cave in northern Rhodesia. A nearly complete skull was found, though without lower jaw; a small piece of the upper jaw of a second individual; and several other bones, including a tibia. The remains were ninety feet deep in a cave, associated with vast quantities of mineralized animal bones. Their age however is unknown. The associated fauna is one of living species only; but this does not imply the same recency as in Europe, since the animal life of Africa has altered relatively little since well back in the Pleistocene.

Measurements of Rhodesian man have not yet been published. The available descriptions point to a small brain case with low vault in the frontal region; more extremely developed eyebrow ridges than in any living or fossil race of man, including Pithecanthropus; a large gorilla-like face, with marked prognathism and a long stretch between nose and teeth—the area covered by the upper lip; a flaring but probably fairly prominent nose; an enormous palate and dental arch—too large to accommodate even the massive Heidelberg jaw; large teeth, but without the projecting canines of the apes and of the lower jaw attributed to Piltdown man; and a forward position of the foramen magnum—the aperture by which the spinal cord enters the brain—which suggests a fully upright position. The same inference is derivable from the long, straight shin-bone.

On the whole, this seems to be a form most closely allied to Neandertal man, though differing from him in numerous respects, and especially in the more primitive type of face. It is well to remember, however, that of none of the forms anterior to Neandertal man—Pithecanthropus, Heidelberg, Piltdown—has the face been recovered. If these were known, the Rhodesian face might seem less impressively ape-like. It is also important to observe that relatively primitive and advanced features exist side by side in Rhodesian man; the face and eyebrow ridges are somewhat off-set by the prominent nose, erect posture, and long clean limb bones. It is therefore likely that this form was a collateral relative of Neandertal man rather than his ancestor or descendant. Its place in the history of the human species can probably be fixed only after the age of the bones is determined. Yet it is already clear that the discovery is important in at least three respects. It reveals the most ape-like face yet found in a human variety; it extends the record of fossil man to a new continent; and that continent is the home of the two living apes—the gorilla and chimpanzee—recognized as most similar to man.

16. The Cro-Magnon Race

The Cro-Magnon race is not only within the human species, but possibly among the ancestors of modern Europeans. While Neandertal man is still Homo Neandertalensis—the genus of living man, but a different species—the Cro-Magnon type is Homo sapiens—that is, a variety of ourselves. The age is that of the gradual, fluctuating retreat of the glaciers—the later Cave period of the Old Stone Age: the Upper Palæolithic, in technical language, comprising the Aurignacian, the Solutrean, and the Magdalenian (§ 70). In years, this was the time from 25,000 to 10,000 B.C.

Some Important Remains of Cro-Magnon Type

The Cro-Magnon race of Aurignacian times, as represented by the finds at Cro-Magnon and Grimaldi,[2] was excessively tall and large-brained, surpassing any living race of man in both respects.

The adult male buried at Cro-Magnon measured 5 feet 11 inches in life; five men at Grimaldi measured from 5 feet 10½ inches to 6 feet 4½ inches, averaging 6 feet 1½ inches. The tallest men now on earth, certain Scots and Negroes, average less than 5 feet 11 inches. A girl at Grimaldi measured 5 feet 5 inches. This race was not only tall, but clean-limbed, lithe, and swift.

Their brains were equally large. Those of the five male skulls from Grimaldi contain from over 1,700 to nearly 1,900 c.c.—an average of 1,800 c.c.; that of the old man of Cro-Magnon, nearly 1,600 c.c.; of a woman there, 1,550 c.c. If these individuals were not exceptional, the figures mean that the size and weight of the brain of the early Cro-Magnon people was some fifteen or twenty per cent greater than that of modern Europeans.

The cephalic index is low—that is, the skull was long and narrow, as in all the types here considered; but the face was particularly broad. The forehead rose well domed; the supraorbital development was moderate, as in recent men; the features must have been attractive even by our standards.

Three of the best preserved skeletons of the Magdalenian period are those of women. Their statures run 4 feet 7 inches, 5 feet 1 inch, 5 feet 1 inch, which would indicate a corresponding normal height for men not far from that of the average European of to-day. The male from Obercassel attained a stature of about 5 feet 3 inches, a cranial capacity of 1,500 c.c., and combined a long skull with a wide face. The general type of the Magdalenian period might be described as a reduced Cro-Magnon one.

The Cro-Magnon peoples used skilfully made harpoons, originated a remarkable art, and in general attained a development of industries parallel to their high degree of bodily progress.

17. The Brünn Race

Several remains have been found in central Europe which have sometimes been considered as belonging to the Neandertal race and sometimes to the subsequent Cro-Magnon race, but do not belong clearly with either, and may perhaps be regarded as distinct from both and possibly bridging them. The type is generally known as the Brünn race. Its habitat was Czecho-Slovakia and perhaps adjacent districts; its epoch, postglacial, in the Solutrean period of the Upper Palæolithic (§ 70). The Brünn race, so far as present knowledge of it goes, was therefore both preceded and succeeded by Cro-Magnon man.

The Brünn race belongs with modern man: its species is no longer Homo Neandertalensis, but Homo sapiens, to which we also belong. The heavy supraorbital ridges of the earlier type are now divided by a depression over the nose instead of stretching continuously across the forehead; the chin is becoming pronounced, the jaws protrude less than in Neandertal man. The skull is somewhat higher and better vaulted. In all these respects there is an approach to the Cro-Magnon race. But the distinctively broad face of the Cro-Magnon people is not in evidence.

A skull of uncertain geologic age, found in 1888 at Galley Hill, near London, is by some linked with the Brünn race. The same is true of an unusually well preserved skeleton found in 1909 at Combe-Capelle, in Périgord, southern France. The period of the Combe-Capelle skeleton is Upper Palæolithic Aurignacian. This was part of the era of the Cro-Magnon race in western Europe; and as the Combe-Capelle remains do not differ much from the Cro-Magnon type, they are best considered as belonging to it.

18. The Grimaldi Race: Neolithic Races

The Grimaldi race is to date represented by only two skeletons, those of a woman and a youth—possibly mother and son—found in 1906 in a grotto at Grimaldi near Mentone, in Italy, close to the French border. They reposed in lower layers, above which subsequent Cro-Magnon burials of Aurignacian date had been made. Their age is therefore early Aurignacian: the beginning of the Upper Palæolithic or later Cave period of the Old Stone Age. The statures are 5 feet 2 inches and 5 feet 1 inch—the youth was not fully grown; the skull capacities 1,375 and nearly 1,600 c.c.

The outstanding feature of both skeletons is that they bear a number of Negroid characteristics. The forearm and lower leg are long as compared with the upper arm and thigh; the pelvis high and small; the jaws prognathous, the nose flat, the eye orbits narrow. All these are Negro traits. This is important, in view of the fact that all the other ancient fossils of men are either more primitive than the living races or, like Cro-Magnon, perhaps ancestral to the Caucasian race.

No fossil remains of any ancestral Mongolian type have yet been discovered.

The New Stone Age, beginning about 10,000 or 8,000 B.C., brings the Grenelle and other types of man; but these are so essentially modern that they need not be considered here. In the Neolithic period, broad heads are for the first time encountered, as they occur at present in Europe and other continents, alongside of narrow ones. The virtual fixity of the human type for these last ten thousand years is by no means incredible. Egyptian mummies and skeletons prove that the type of that country has changed little in five thousand years except as the result of invasions and admixture.

19. The Metric Expression of Human Evolution

The relations of the several fossil types of man and their gradual progression are most accurately expressed by certain skull angles and proportions, or indexes, which have been specially devised for the purpose. The anthropometric criteria that are of most importance in the study of living races, more or less fail in regard to prehistoric man. The hair, complexion, and eye-color are not preserved. The head breadth, as indicated by the cephalic index, is substantially the same from Pithecanthropus to the last Cro-Magnons. Stature on the other hand varies from one to another ancient race without evincing much tendency to grow or to diminish consistently. Often, too, there is only part of a skull preserved. The following proportions of the top or vault of the skull—the calvarium—are therefore useful for expressing quantitatively the gradual physical progress of humanity from its beginning.

Three anatomical points on the surface of the skull are the pivots on which these special indexes and angles rest. One is the Glabella (G in figure 7), the slight swelling situated between the eyebrows and above the root of the nose. The second is the Inion (I), the most rearward point on the skull. The third is the Bregma (B) or point of intersection of the sutures which divide the frontal from the parietal bones. The bregma falls at or very near the highest point of the skull.

If now we see a skull lengthwise, or draw a projection of it, and connect the glabella and the inion by a line GI, and the glabella and the bregma by a line GB, an acute angle, BGI, is formed. This is the “bregma angle.” Obviously a high vaulted skull or one that has the superior point B well forward will show a greater angle than a low flat skull or one with its summit lying far back.

Next, let us drop a vertical from the bregma to the line GI, cutting it at X. Obviously the proportion which the vertical line BX bears to the horizontal line GI will be greater or less as the arch or vault of the brain case is higher or lower. This proportion BX: GI, expressed in percentages, is the “calvarial height index.”

The Skull of Modern and Fossil Man

If now we compute the proportion of the GX part of the line GI to the whole of this line, we have the “bregma position index”; that is, a numerical indication of how far forward on the skull the highest point B lies. A sloping or retreating forehead naturally tends to have the bregma rearward; whereas if the frontal bone is nearly vertical, resulting in a high, domed expanse of forehead, the bregma tends to be situated farther forward, the point X shifts in the same direction, the distance GX becomes shorter in comparison to the whole line GI, and the “bregma position index” falls numerically.

The “frontal angle,” finally, is determined by drawing a line GF from the glabella tangent to the most protruding part of the frontal bone and measuring the angle between this and the horizontal GI. A small frontal angle obviously means a receding forehead.

All these data can be obtained from the mere upper fragment of a skull; they relate to that feature which is probably of the greatest importance in the evolution of man from the lower animals—the development of the brain case and therefore of the brain, especially of the cerebrum or fore-brain; and they define this evolution rather convincingly. The table, which compiles some of the most important findings, shows that progress has been fairly steadily continuous in the direction of greater cerebral development.