Darwin, and After Darwin Volume I Part 3

[Ill.u.s.tration: FIG. 11.--Rudimentary, or vestigial and useless, muscles of the human ear. (From _Gray's Anatomy_.)]

(2) _Panniculus carnosis._--A large number of the mammalia are able to move their skin by means of sub-cutaneous muscle--as we see, for instance, in a horse, when thus protecting himself against the sucking of flies. We, in common with the Quadrumana, possess an active remnant of such a muscle in the skin of the forehead, whereby we draw up the eyebrows; but we are no longer able to use other considerable remnants of it, in the scalp and elsewhere,--or, more correctly, it is rarely that we meet with persons who can. But most of the Quadrumana (including the anthropoids) are still able to do so. There are also many other vestigial muscles, which occur only in a small percentage of human beings, but which, when they do occur, present unmistakeable h.o.m.ologies with normal muscles in some of the Quadrumana and still lower animals[5].

[5] See especially Mr. John Wood's papers, _Proc. R. S._, xiii to xvi, and xviii; also _Journ. Anat._, i and iii. In this connexion Darwin refers to M. Richard, _Annls. d. Sc. Nat. Zoolg._, tom.

xviii, p. 13, 1852.

(3) _Feet._--It is observable that in the infant the feet have a strong deflection inwards, so that the soles in considerable measure face one another. This peculiarity, which is even more marked in the embryo than in the infant (see p. 153), and which becomes gradually less and less conspicuous even before the child begins to walk, appears to me a highly suggestive peculiarity. For it plainly refers to the condition of things in the Quadrumana, seeing that in all these animals the feet are similarly curved inwards, to facilitate the grasping of branches. And even when walking on the ground apes and monkeys employ to a great extent the outside edges of their feet, as does also a child when learning to walk. The feet of a young child are also extraordinarily mobile in all directions, as are those of apes. In order to show these points, I here introduce comparative drawings of a young ape and the portrait of a young male child. These drawings, moreover, serve at the same time to ill.u.s.trate two other vestigial characters, which have often been previously noticed with regard to the infant's foot. I allude to the incurved form of the legs, and the lateral extension of the great toe, whereby it approaches the thumb-like character of this organ in the Quadrumana. As in the case of the incurved position of the legs and feet, so in this case of the lateral extensibility of the great toe, the peculiarity is even more marked in embryonic than in infant life. For, as Prof. Wyman has remarked with regard to the foetus when about an inch in length, "The great toe is shorter than the others; and, instead of being parallel to them, is projected at an angle from the side of the foot, thus corresponding with the permanent condition of this part in the Quadrumana[6]." So that this organ, which, according to Owen, "is perhaps the most characteristic peculiarity in the human structure,"

when traced back to the early stages of its development, is found to present a notably less degree of peculiarity.

[6] _Proc. Nat. Hist. Soc._, Boston, 1863.

[Ill.u.s.tration: FIG. 12.--Portrait of a young male gorilla (after Hartmann).]

[Ill.u.s.tration: FIG. 13.--Portrait of a young male child.

Photographed from life, when the mobile feet were for a short time at rest in a position of extreme inflection.]

(4) _Hands._--Dr. Louis Robinson has recently observed that the grasping power of the whole human hand is so surprisingly great at birth, and during the first few weeks of infancy, as to be far in excess of present requirements on the part of a young child. Hence he concludes that it refers us to our quadrumanous ancestry--the young of anthropoid apes being endowed with similar powers of grasping, in order to hold on to the hair of the mother when she is using her arms for the purposes of locomotion. This inference appears to me justifiable, inasmuch as no other explanation can be given of the comparatively inordinate muscular force of an infant's grip. For experiments showed that very young babies are able to support their own weight, by holding on to a horizontal bar, for a period varying from one half to more than two minutes[7]. With his kind permission I here reproduce one of Dr. Robinson's instantaneous, and hitherto unpublished, photographs of a very young infant. This photograph was taken after the above paragraph (3) was written, and I introduce it here because it serves to show incidentally--and perhaps even better than the preceding figure--the points there mentioned with regard to the feet and great toes. Again, as Dr. Robinson observes, the att.i.tude, and the disproportionately large development of the arms as compared with the legs, give all the photographs a striking resemblance to a picture of the chimpanzee "Sally" at the Zoological Gardens. For "invariably the thighs are bent nearly at right angles to the body, and in no case did the lower limbs hang down and take the att.i.tude of the erect position." He adds, "In many cases no sign of distress is evinced, and no cry uttered, until the grasp begins to give way."

[7] _Nineteenth Century_, November, 1891.

[Ill.u.s.tration: FIG. 14.--An infant, three weeks old, supporting its own weight for over two minutes. The att.i.tude of the lower limbs, feet, and toes, is strikingly simian. Reproduced from an instantaneous photograph, kindly given for the purpose by Dr. L.

Robinson.]

(5) _Tail._--The absence of a tail in man is popularly supposed to const.i.tute a difficulty against the doctrine of his quadrumanous descent. As a matter of fact, however, the absence of an external tail in man is precisely what this doctrine would expect, seeing that the nearest allies of man in the quadrumanous series are likewise dest.i.tute of an external tail. Far, then, from this deficiency in man const.i.tuting any difficulty to be accounted for, if the case were not so--i. e. if man _did_ possess an external tail,--the difficulty would be to understand how he had managed to retain an organ which had been renounced by his most recent ancestors. Nevertheless, as the anthropoid apes continue to present the rudimentary vestiges of a tail in a few caudal vertebrae below the integuments, we might well expect to find a similar state of matters in the case of man. And this is just what we do find, as a glance at these two comparative ill.u.s.trations will show.

(Fig. 15.) Moreover, during embryonic life, both of the anthropoid apes and of man, the tail much more closely resembles that of the lower kinds of quadrumanous animals from which these higher representatives of the group have descended. For at a certain stage of embryonic life the tail, both of apes and of human beings, is actually longer than the legs (see Fig. 16). And at this stage of development, also, the tail admits of being moved by muscles which later on dwindle away. Occasionally, however, these muscles persist, and are then described by anatomists as abnormalities. The following ill.u.s.trations serve to show the muscles in question, when thus found in adult man.

[Ill.u.s.tration: FIG. 15.--Sacrum of Gorilla compared with that of Man, showing the rudimentary tail-bones of each. Drawn from nature (_R. Coll. Surg. Mus._).]

[Ill.u.s.tration: FIG. 16.--Diagrammatic outline of the human embryo when about seven weeks old, showing the relations of the limbs and tail to the trunk (after Allen Thomson), _r_, the radial, and _u_, the ulnar, border of the hand and fore-arm; _t_, the tibial, and _f_, the fibular, border of the foot and lower leg; _au_, ear; _s_, spinal cord; _v_, umbilical cord; _b_, branchial gill-slits; _c_, tail.]

[Ill.u.s.tration: FIG. 17.--Front and back view of adult human sacrum, showing abnormal persistence of vestigial tail-muscles. (The first drawing is copied from Prof. Watson's paper in _Journl. Anat. and Physiol._, vol. 79: the second is compiled from different specimens.)]

(6) _Vermiform Appendix of the Caec.u.m._--This is of large size and functional use in the process of digestion among many herbivorous animals; while in man it is not only too small to serve any such purpose, but is even a source of danger to life--many persons dying every year from inflammation set up by the lodgement in this blind tube of fruit-stones, &c.

In the orang it is longer than in man (Fig. 18), as it is also in the human foetus proportionally compared with the adult. (Fig. 19.) In some of the lower herbivorous animals it is longer than the entire body.

Like vestigial structures in general, however, this one is highly variable. Thus the above cut (Fig. 19) serves to show that it may sometimes be almost as short in the orang as it normally is in man--both the human subjects of this ill.u.s.tration having been normal.

[Ill.u.s.tration: FIG. 18.--_Appendix vermiformis_ in Orang and in Man.

Drawn from dried inflated specimens in the Cambridge Museum by Mr.

J. J. Lister. _Il_, ilium; _Co_, colon; _C_, caec.u.m; W, a window cut in the wall of the caec.u.m; X X X, the appendix.]

[Ill.u.s.tration: FIG. 19.--The same, showing variation in the Orang.

Drawn from a specimen in the Museum of the Royal College of Surgeons.]

(7) _Ear._--Mr. Darwin writes:--

The celebrated sculptor, Mr. Woolner, informs me of one little peculiarity in the external ear, which he has often observed both in men and women.... The peculiarity consists in a little blunt point, projecting from the inwardly folded margin, or helix. When present, it is developed at birth, and, according to Prof. Ludwig Meyer, more frequently in man than in woman. Mr. Woolner made an exact model of one such case, and sent me the accompanying drawing.... The helix obviously consists of the extreme margin of the ear folded inwards; and the folding appears to be in some manner connected with the whole external ear being permanently pressed backwards. In many monkeys, which do not stand high in the order, as baboons and some species of macacus, the upper portion of the ear is slightly pointed, and the margin is not at all folded inwards; but if the margin were to be thus folded, a slight point would necessarily project towards the centre.... The following wood-cut is an accurate copy of a photograph of the foetus of an orang (kindly sent me by Dr. Nitsche), in which it may be seen how different the pointed outline of the ear is at this period from its adult condition, when it bears a close general resemblance to that of man [including even the occasional appearance of the projecting point shown in the preceding woodcut]. It is evident that the folding over of the tip of such an ear, unless it changed greatly during its further development, would give rise to a point projecting inwards[8].

[8] _Descent of Man_, 2nd ed., pp. 15-16.

[Ill.u.s.tration: FIG. 20.--Human ear, modelled and drawn by Mr.

Woolner. _a_, the projecting point.]

[Ill.u.s.tration: FIG. 21.--Foetus of an Orang. Exact copy of a photograph, showing the form of the ear at this early stage.]

The following woodcut serves still further to show vestigial resemblances between the human ear and that of apes. The last two figures ill.u.s.trate the general resemblance between the normal ear of foetal man and the ear of an adult orang-outang. The other two figures on the lower line are intended to exhibit occasional modifications of the adult human ear, which approximate simian characters somewhat more closely than does the normal type. It will be observed that in their comparatively small lobes these ears resemble those of all the apes; and that while the outer margin of one is not unlike that of the Barbary ape, the outer margin of the other follows those of the chimpanzee and orang. Of course it would be easy to select individual human ears which present either of these characters in a more p.r.o.nounced degree; but these ears have been chosen as models because they present both characters in conjunction. The upper row of figures likewise shows the close similarity of hair-tracts, and the direction of growth on the part of the hair itself, in cases where the human ear happens to be of an abnormally hirsute character. But this particular instance (which I do not think has been previously noticed) introduces us to the subject of hair, and hair-growth, in general.

[Ill.u.s.tration: FIG. 22.--Vestigial characters of human ears. Drawn from nature.]

(8) _Hair._--Adult man presents rudimentary hair over most parts of the body. Wallace has sought to draw a refined distinction between this vestigial coating and the useful coating of quadrumanous animals, in the absence of the former from the human back. But even this refined distinction does not hold. On the one hand, the comparatively hairless chimpanzee which died last year in the Zoological Gardens (_T. calvus_) was remarkably denuded over the back; and, on the other hand, men who present a considerable development of hair over the rest of their bodies present it also on their backs and shoulders. Again, in all men the rudimentary hair on the upper and lower arm is directed towards the elbow--a peculiarity which occurs nowhere else in the animal kingdom, with the exception of the anthropoid apes and a few American monkeys, where it presumably has to do with arboreal habits. For, when sitting in trees, the orang, as observed by Mr. Wallace, places its hands above its head with its elbows pointing downwards: the disposition of hair on the arms and fore-arms then has the effect of thatch in turning the rain. Again, I find that in all species of apes, monkeys, and baboons which I have examined (and they have been numerous), the hair on the backs of the hands and feet is continued as far as the first row of phalanges; but becomes scanty, or disappears altogether, on the second row; while it is invariably absent on the terminal row. I also find that the same peculiarity occurs in man. We all have rudimentary hair on the first row of phalanges, both of hands and feet: when present at all, it is more scanty on the second row; and in no case have I been able to find any on the terminal row. In all cases these peculiarities are congenital, and the total absence or partial presence of hair on the second phalanges is constant in different species of Quadrumana. For instance, it is entirely absent in all the chimpanzees, which I have examined, while scantily present in all the orangs. As in man, it occurs in a patch midway between the joints.

[Ill.u.s.tration: FIG. 23.--Hair-tracts on the arms and hands of Man, as compared with those on the arms and hands of Chimpanzee. Drawn from life.]

Besides showing these two features with regard to the disposition of hair on the human arm and hand, the above woodcut ill.u.s.trates a third.

By looking closely at the arm of the very hairy man from whom the drawing was taken, it could be seen that there was a strong tendency towards a whorled arrangement of the hairs on the backs of the wrists.

This is likewise, as a general rule, a marked feature in the arrangement of hair on the same places in the gorilla, orang, and chimpanzee. In the specimen of the latter, however, from which the drawing was taken, this characteristic was not well marked. The downward direction of the hair on the backs of the hands is exactly the same in man as it is in all the anthropoid apes. Again, with regard to hair, Darwin notices that occasionally there appears in man a few hairs in the eyebrows much longer than the others; and that they seem to be representative of similarly long and scattered hairs which occur in the chimpanzee, macacus, and baboons.

Lastly, it may be here more conveniently observed than in the next chapter on Embryology, that at about the sixth month the human foetus is often thickly coated with somewhat long dark hair over the entire body, except the soles of the feet and palms of the hands, which are likewise bare in all quadrumanous animals. This covering, which is called the lanugo, and sometimes extends even to the whole forehead, ears, and face, is shed before birth. So that it appears to be useless for any purpose other than that of emphatically declaring man a child of the monkey.

(9) _Teeth._--Darwin writes:--

It appears as if the posterior molar or wisdom-teeth were tending to become rudimentary in the more civilized races of man. These teeth are rather smaller than the other molars, as is likewise the case with the corresponding teeth in the chimpanzee and orang; and they have only two separate fangs.... They are also much more liable to vary, both in structure and in the period of their development, than the other teeth. In the Melanian races, on the other hand, the wisdom-teeth are usually furnished with three separate fangs, and are usually sound [i. e. not specially liable to decay]; they also differ from the other molars in size, less than in the Caucasian races.

Now, in addition to these there are other respects in which the dwindling condition of wisdom-teeth is manifested--particularly with regard to the pattern of their crowns. Indeed, in this respect it would seem that even in the anthropoid apes there is the beginning of a tendency to degeneration of the molar teeth from behind forwards. For if we compare the three molars in the lower jaw of the gorilla, orang, and chimpanzee, we find that the gorilla has five well-marked cusps on all three of them; but that in the orang the cusps are not so p.r.o.nounced, while in the chimpanzee there are only four of them on the third molar.

Now in man it is only the first of these three teeth which normally presents five cusps, both the others presenting only four. So that, comparing all these genera together, it appears that the number of cusps is being reduced from behind forwards; the chimpanzee having lost one of them from the third molar, while man has not only lost this, but also one from the second molar,--and, it may be added, likewise partially (or even totally) from the first molar, as a frequent variation among civilized races. But, on the other hand, variations are often met with in the opposite direction, where the second or the third molar of man presents five cusps--in the one case following the chimpanzee, in the other the gorilla. These latter variations, therefore, may fairly be regarded as reversionary. For these facts I am indebted to the kindness of Mr. C. S. Tomes.

[Ill.u.s.tration: FIG. 24.--Molar teeth of lower jaw in Gorilla, Orang, and Man. Drawn from nature, nat. size (_R. Mus. Coll. Surg._).]

(10) _Perforations of the humerus._--The peculiarities which we have to notice under this heading are two in number. First, the supra condyloid foramen is a normal feature in some of the lower Quadrumana (Fig. 25), where it gives pa.s.sage to the great nerve of the fore-arm, and often also to the great artery. In man, however, it is not a normal feature.

Yet it occurs in a small percentage of cases--viz., according to Sir W.

Turner, in about one per cent., and therefore is regarded by Darwin as a vestigial character. Secondly, there is inter-condyloid foramen, which is also situated near the lower end of the humerus, but more in the middle of the bone. This occurs, but not constantly, in apes, and also in the human species. From the fact that it does so much more frequently in the bones of ancient--and also of some savage--races of mankind (viz.

in 20 to 30 per cent. of cases), Darwin is disposed to regard it also as a vestigial feature. On the other hand, Prof. Flower tells me that in his opinion it is but an expression of impoverished nutrition during the growth of the bone.

[Ill.u.s.tration: FIG. 25.--Perforation of the humerus (supra-condyloid foramen) in three species of Quadrumana where it normally occurs, and in Man, where it does not normally occur. Drawn from nature (_R.

Coll. Surg. Mus._).]

(11) _Flattening of tibia._--In some very ancient human skeletons, there has also been found a lateral flattening of the tibia, which rarely occurs in any existing human beings, but which appears to have been usual among the earliest races of mankind hitherto discovered. According to Broca, the measurements of these fossil human tibiae resemble those of apes. Moreover, the bone is bent and strongly convex forwards, while its angles are so rounded as to present the nearly oval section seen in apes. It is in a.s.sociation with these ape-like human tibiae that perforated humeri of man are found in greatest abundance.

On the other hand, however, there is reason to doubt whether this form of tibia in man is really a survival from his quadrumanous ancestry.

For, as Boyd-Dawkins and Hartmann have pointed out, the degree of flattening presented by some of these ancient human bones is _greater_ than that which occurs in any existing species of anthropoid ape. Of course the possibility remains that the unknown species of ape from which man descended may have had its tibia more flattened than is now observable in any of the existing species. Nevertheless, as some doubt attaches to this particular case, I do not press it--and, indeed, only mention it at all in order that the doubt may be expressed.

Similarly, I will conclude by remarking that several other instances of the survival of vestigial structures in man have been alleged, which are of a still more doubtful character. Of such, for example, are the supposed absence of the genial tubercle in the case of a very ancient jaw-bone of man, and the disposition of valves in human veins. From the former it was argued that the possessor of this very ancient jaw-bone was probably speechless, inasmuch as the tubercle in existing man gives attachment to muscles of the tongue. From the latter it has been argued that all the valves in the veins of the human body have reference, in their disposition, to the incidence of blood-pressure when the att.i.tude of the body is horizontal, or quadrupedal. Now, the former case has already broken down, and I find that the latter does not hold. But we can well afford to lose such doubtful and spurious cases, in view of all the foregoing unquestionable and genuine cases of vestigial structures which are to be met with even within the limits of our own organization--and even when these limits are still further limited by selecting only those instances which refer to the very latest chapter of our long ancestral history.

CHAPTER IV.