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.
Fig. 7. Indices and angles of special significance in the change from fossil to living man. Calvarial height index, BX: GI. Bregma position index, GX: GI. Bregma angle, BGI. Frontal angle, FGI.
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
| Calvarial Height Index | Bregma Angle | Bregma Position Index | Frontal Angle | |
|---|---|---|---|---|
| Maximum for modern man | 68 | 66 | ||
| Average for modern man | 59 | 58 | 30.5 | 90 |
| 90 Central Europeans | 60 | 61 | 31 | |
| 28 Bantu Negroes | 59 | 59 | 31 | |
| 7 Greenland Eskimos | 56 | 58 | 30 | |
| 43 Australian natives | 56 | 57.5 | (33) | |
| 8 Tasmanian natives | 56 | 57 | ||
| Minimum for modern man | 47.5 | 46 | 37 | 72 |
| Chancelade | 57 | 60 | ||
| Combe-Capelle | 54.5 | 58 | ||
| Aurignac | 54.5 | |||
| Cro-Magnon I | 50 | 54 | 33 | |
| Brünn I | 51 | 52 | 75 | |
| Galley Hill | 48 | 52 | 82 | |
| Brüx | 48 | 51? | 75? | |
| Le Moustier | 47 | |||
| Krapina C | 46 | 52 | 70 | |
| Spy II | 44 | 50 | 35 | 67 |
| Krapina D | 42 | 50 | 32 | 66 |
| Chapelle-aux-Saints | 40.5 | 45.5 | 36.5 | 65 |
| Spy I | 41 | 45 | 35 | 57.5 |
| Gibraltar | 40 | 50 | 73? | |
| Neandertal | 40 | 44 | 38 | 62 |
| Pithecanthropus | 34 | 38 | 42 | 52.5 |
| Maximum for any Anthropoid ape | 38 | 39.5 | 63 | |
| Chimpanzee | 32 | 34 | 47 | 56 |
| Gorilla | 20 | 22 | 42 | |
| Orang-utan | 27 | 32 | 45 | |
| Summarized Averages | ||||
| Modern races | 59 | 58 | 31 | 90 |
| Cro-Magnon race | 54 | 57 | 33 | |
| Brünn race | 49 | 52 | 77 | |
| Neandertal man | 42 | 48 | 35 | 66 |
| Pithecanthropus | 34 | 38 | 42 | 52 |
| Anthropoid apes | 26 | 30 | 45 | |
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.
CHAPTER III
LIVING RACES
[20.] Race origins.—[21.] Race classification.—[22.] Traits on which classification rests.—[23.] The grand divisions or primary stocks.—[24.] Caucasian races.—[25.] Mongoloid races.—[26.] Negroid races.—[27.] Peoples of doubtful position.—[28.] Continents and oceans.—[29.] The history of race classifications.—[30.] Emergence of the threefold classification.—[31.] Other classifications.—[32.] Principles and conclusions common to all classifications.—[33.] Race, nationality, and language.