§ 1. Two Theories of Descent

Two theories have been formulated regarding the alleged bestial origin of the human body: (1) the theory of lineal descent from some known species (living or fossil) of ape or monkey; (2) the theory of collateral descent from a hypothetical bestial ancestor common to apes and men. The theory of lineal descent is that to which Darwin himself stands committed. This theory, however, soon fell into disrepute among scientists, who came to prefer the theory of collateral descent, although signs of a return to the older theory are not wanting in our day. At all events, Darwin came out flatly in favor of the monkey origin of man. This, it is true, has been indignantly denied by loyal partisans anxious to exonerate their idol from the reproach of having advanced a crude and now obsolete theory of human descent. But Darwin’s own words speak for themselves: “The Simiadae,” he says, “then branched off into two great stems, the New World and Old World monkeys; and from the latter, at a remote period of time, Man, the wonder and glory of the Universe, proceeded.” (“Descent of Man,” 2nd ed., ch. VI, pp. 220, 221.) Note that he does not say “probably”; his language is not the language of hypothesis, but of categorical affirmation.

The theory, however, which is most generally favored at the present time holds that, assuming the universality of the evolutionary process, all existing types must be of equal antiquity, and none prior or ancestral to any other. Hence it regards man, not as the direct descendant of any known type of ape, but as the offspring of an as yet undiscovered Tertiary ancestor, from which men and apes have diverged in two distinct lines of descent. “Monkeys, apes, and men,” says Conklin, “have descended from some common but at present extinct ancestor. Existing apes and monkeys are collateral relatives of man but not his ancestors; his cousins but not his parents.... The human branch diverged from the anthropoid stock not less than two million years ago, and since that time man has been evolving in the direction represented by existing human races, while the apes have been evolving in the direction represented by existing anthropoids. During all this time men and apes have been growing more and more unlike and conversely the farther back we go, the more we should find them converging until they meet in a common stock which should be intermediate between these two stocks.” (“Evolution and the Bible,” pp. 12, 13—italics his.)

Barnum Brown’s recent discovery of three jaws of the fossil ape Dryopithecus in the Siwalik Hills of India has, as previously intimated, resulted in a return on the part of certain scientists, e.g. Wm. K. Gregory and Dudley J. Morton, to views that more nearly approximate those of Charles Darwin. According to these men, the fossil anthropoid Dryopithecus is to be regarded as the common ancestor of men, chimpanzees, and gorillas. (Cf. Science, April 25, 1924, Suppl. XII.)

Many considerations, however, militate against the direct derivation of man’s bodily frame from any known species of ape, whether living or fossil. Dana has pointed out that, as regards the mechanism of locomotion, man belongs to a more primitive type than the ape. The earliest and lowest type of vertebrates are the fish, and these, according to the above-mentioned author, are urosthenic (tail-strong), inasmuch as they propel themselves by means of their tails. Next in point of organization and time came the merosthenic vertebrates, which have their strength concentrated in the hind-limbs, e.g. reptiles like the dinosaurs. In the last place come the prosthenic vertebrates, whose strength is concentrated in the fore-limbs, e.g. the carnivora and apes. Now man belongs to the merosthenic type, and his mode of progression, therefore, is more primitive than that of apes, which are prosthenic, all anthropoid apes, such as the gorilla, the chimpanzee, the orang-utan and the gibbon having longer fore-limbs than hind-limbs.

The striking anatomical differences between apes and men, though not of sufficient importance to exclude the possibility of collateral relationship, are so many solid arguments against the theory of direct descent. We will content ourselves with a mere enumeration of these differences. In the ape, the cranium has a protruding muzzle and powerful jaws equipped with projecting canine teeth, but the brain-case is comparatively small; in man, on the contrary, the facial development is insignificant and the teeth are small and vertical, while the brain-case is enormous in size, having at least twice the capacity of that of an ape. “The face of man,” to quote Ranke, “slides, as it were, down from the forehead and appears as an appendix to the front half of the skull. But the gorilla’s face, on the contrary, protrudes from the skull, which in turn slides almost entirely backward from the face. By a cross-cut one may sever the whole face from the skull, except a very small part near the sockets, without being forced to open up the interior of the skull. It is only on account of its protruding, strongly developed lower parts that the skull-cap of the animal can simulate a kind of human face.” (“Der Mensch,” vol. II, p. 401.) These differences may be summarized by saying that the head of the ape is specialized for mastication and defense, whereas the head of man is specialized for psychic functions. Again, as we have seen, the fore-limbs of the ape are long, and its hind-limbs short, the extremities of both the latter and the former being specialized primarily for prehension and only secondarily for progression. This is due to the ape’s adaptation to arboreal life. In man, however, the arms are short and specialized for prehension alone, while the legs are long and terminate in broad plantigrade feet specialized for progression alone. Man, consequently, is not adapted to arboreal life. In the ape, the spine has a single curve, and the occipital foramen (the aperture through which the spinal cord enters the brain-case) is eccentrically located in the floor of the cranial box; in man, the spine has a double curve, and the occipital foramen is centrally located, both features being in adaptation to the upright posture peculiar to man—“die zentralle Lage dieser Oeffnung,” says Ranke alluding to the occipital foramen of man, “in der Schädelbasis ist für den Menschenschädel im Unterschied gegen den Tierschädel eine in hohem Masse typische.” (“Der Mensch,” vol. I, p. 378.) In the ape, therefore, the vertebræ have an adaptation producing convexity of the back, precluding a normal upright posture, and enforcing progression on all fours. It has, moreover, powerful muscles at the back of the neck to carry the head in the horizontal position necessitated by this mode of progression. In man “the skull has the occipital condyles placed within the middle fifth, in adaptation to the vertical position of the spine” (Nicholson), the spinal cord enters the cranial box at a perpendicular, and the head balances on the spinal column as on a pivot, all of which ensures the erect posture and bipedal progression in man. There are, moreover, no neck muscles to support the head in any other than the vertical position. There are many other differences, besides: the ape, for example, has no chin, while in man there is a marked mental protuberance; man has a slender waist, but the ape has a barrel-like torso without any waist; the ape has huge bony ridges for the attachment of muscles, e.g. the sagittal crest, the superciliary ridges, etc., while in man such features are practically absent.

Ranke has given a very good summary of the chief anatomical differences between man and the anthropoid apes: “The gorilla’s head leaning forward, hangs down from the spinal column, and his chinless snout, equipped with powerful teeth, touches the breastbone. Man’s head is round, and resting on a free neck, balances unrestrained upon the spinal column. The gorilla’s body, without a waist, swells out barrel-shaped, and when straightened up finds no sufficient support on the pelvis; the back-bone, tailless as in man, but almost straight, loses itself without nape or neck formation properly so-called in the rear part of the head and without protuberance of the gluteal region in the flat thighs. Man’s body is slightly molded, like an hour-glass, the chest and abdomen meeting to form a waist where they are narrowest; the abdominal viscera are perfectly supported in the pelvis as in a plate; and elegance is decidedly gained by the double S-line, which, curving alternately convex and concave, passes from the crown through the neck and nape, down the back to the base of the spine and the gluteal region. The normal position of the gorilla shows us a plump, bear-like trunk, carried by short, crooked legs and by arms which serve as crutches and touch the ground with the knuckles of the turned-in fingers. The posture of the body is perfectly straight in man, it rests on the legs as on columns when he stands upright, and his hands hang down on both sides always ready for use. The gorilla is thickly covered with hair, while man’s body on the whole is naked.” (Op. cit., vol. II, p. 213.)

In conclusion, we may say that, while there is a general resemblance between the human body and that of an anthropoid ape, there is, likewise, a particular divergence—“there is no bone, be it ever so small, nay, not even the smallest particle of a bone, in which the general agreement in structure and function would pass over into real identity.” (Ranke, op. cit., vol. I, p. 437.) Hence Virchow declares that “the differences between man and monkey are so wide that almost any fragment is sufficient to diagnose them.” (Smithson. Inst. Rpt. for 1889, p. 566.) These differences are so considerable as to preclude the possibility of a direct genealogical connection between man and any known type of ape or monkey—“The testimony of comparative anatomy,” to quote Bumüller, “is decidedly against the theory of man’s descent from the ape.” (“Mensch oder Affe?” p. 59.) Ranke has somewhere called man a brain-animal, and this sums up the chief difference, which marks off the human body from all bestial organisms. In the ape the brain weighs only 100th part of the weight of its body, whereas in man the brain has a weight equivalent to the 37th part of the weight of the human body. The cranial capacity of the largest apes ranges from 500 to 600 c.cm., while the average cranial capacity in man is 1500 c.cm. Moreover, the human brain is far more extensively convoluted within the brain-case than that of an ape, so much so that the surface or cortical area of the human brain is four times as great as that of the ape’s brain. Thus Wundt, in his “Grundzüge der physiologischen Psychologie,” cites H. Wagner as assigning to man a brain surface of from 2,196 to 1,877 sq. cm., but a cortical area of only 535 sq. cm. in the case of an orang-outang. (Cf. English Translation by Titchener, vol. I, p. 286.)

Another difficulty in the way of the Darwinian theory of direct descent is the fact that the best counterparts of human anatomy are not found united in any one species of ape or monkey, but are scattered throughout a large number of species. “Returning to the old discussion,” says Thomas Dwight, “as to which ape can boast of the closest resemblance to man, Kohlbrugge brings before us Aeby’s forgotten book on the skull of man and apes. His measurements show that the form nearest to man among apes is the gibbon, or long-armed ape, but that the South American monkey Crysothrix is nearer still. Aeby recognized what modern anatomists have forgotten or wilfully ignored: that any system of descent is inadequate which does not recognize that the type of man is not in any one organ, but in all the physical and psychological features. He declared that while we are far from having this universal knowledge, we have learned enough about the various parts of the body to make it impossible for us to sketch any plan of descent. ‘It almost seems as if every part had its own line of descent, different from that of others.’ ... Kohlbrugge now introduces Haacke, who denies any relationship between man and apes, the latter being instances of one-sided development. He even dares to declare anyone who speaks of an intermediate form between man and apes to be ignorant of the laws of development governing the race history of mammals. He believes man came from some lemuroid form, which may have descended from the insectivora.” (“Thoughts of a Catholic Anatomist,” pp. 188-190.)

All known types, then, of apes and monkeys are too specialized to have been in the direct line of human descent. Man, as Kohlbrugge ironically remarks, appears to have come from an ancestor much more like himself than any species of ape we know of. Moreover, no species of apes or monkeys monopolizes the honors of closest resemblance to man. In many points, the South American monkeys, though more primitive than the anthropoid apes, are more similar to man than the latter.