Prehistoric Man

Our knowledge of prehistoric man is based naturally upon the study of certain parts of the human skeleton preserved in a fossil state. In addition to these materials, other evidence is available in the form of certain products of human industry. These include such objects as implements of various kinds, owing their preservation to the almost indestructible nature of their material, or again artistic representations, whether pictorial or glyptic.

The evidence of the bones themselves will be considered first, partly for convenience and partly in view of the cogency possessed by actual remains of the human frame. Other branches of the subject will come under review afterwards.

Of all the discoveries of ancient remains, whether possibly or certainly human, two in particular stand out pre-eminently in marked relief. The specimens thus distinguished are known as the remains of Pithecanthropus erectus, on the one hand, and on the other a jaw-bone which is attributed to a human type described (from the locality of the discovery) as Homo heidelbergensis.

The geological antiquity assigned in each instance is greater than that claimed for any bones acknowledged unreservedly to be human.

It is thus clear that a high value attaches to these specimens if they be regarded as documents testifying to the course of human evolution. When the bones are examined, the contrast they provide with all human remains is so marked as to emphasise at once the necessity for a thorough and critical examination of their structure.

Pithecanthropus erectus.

In the case of these bones, the facts are now so widely known and so easily accessible as to render unnecessary any detailed exposition here. The discoveries were made in the years 1891 and 1892 by Professor Dubois[1], who was engaged at the time on an investigation of the remains of various animals found embedded in a river-bank in Java. As is well known, the actual remains are scanty. They comprise the upper part of a skull, part of a lower jaw (which has never been described), three teeth, and a left thigh-bone.

[1] The numbers refer to the Bibliography at the end of the volume.

Before entering upon any criticism of the results of Professor Dubois' studies, it is convenient to give a general statement of his conclusions. Here we find described a creature of Pliocene age, presenting a form so extraordinary as hardly to be considered human, placed so it seems between the human and simian tribes. It is Caliban, a missing link,-in fact a Pithecanthropus.

With the erect attitude and a stature surpassing that of many modern men were combined the heavy brows and narrow forehead of a flattened skull, containing little more than half the weight of brain possessed by an average European. The molar teeth were large with stout and divergent roots.

The arguments founded upon the joint consideration of the length of the thigh-bone and the capacity of the skull are of the highest interest. For the former dimension provides a means of estimating approximately the body-weight, while the capacity gives an indication of the brain-weight. The body-weight is asserted to have been about 70 kgm. (eleven stone) and the brain-weight about 750 gm. And the ratio of the two weights is approximately 1?94. The corresponding ratios for a large anthropoid ape (Orang-utan) and for man are given in the table following, thus:

Orang-utan 1?183

Pithecanthropus erectus 1?94

Man 1?51

The intermediate position of the Javanese fossil is clearly revealed.

The same sequence is shewn by a series of tracings representative of the cranial arc in the middle line of the head (Fig. 1). And the results of many tests of this kind, applied not only by Professor Dubois but also by Professor Schwalbe, are confirmatory of the 'intermediate' position claimed for Pithecanthropus erectus. The molar teeth are of inadequate size if the skull-cap is that of an ape, whereas they are slightly larger than the corresponding teeth furnished by primitive existing human types. And now some of the objections to this account may be taken.

In the first place, the claim to Pliocene antiquity is contested. So keen an interest was excited by Professor Dubois' discovery that more than one expedition has been dispatched to survey and review the ground. It is now declared in certain quarters that the horizon is lower Quaternary: I do not know that any attempt has been made to reduce the age of the strata further. As the matter stands, the difference is not very material, but Professor Dubois refuses to accept the revised estimate and still adheres to his own determination. Incidentally the more recent work (Blanckenhorn[2], 1910) has resulted in the discovery of a tooth claimed as definitely human (this is not the case with the teeth of Pithecanthropus erectus), and yet of an antiquity surpassing that of the remains found by Professor Dubois. The latter appears unconvinced as to the genuineness of the find, but no doubt the case will be fully discussed in publications now in the course of preparation.

Fig. 1. Outline tracings of skulls reduced in size to a common dimension, viz. the line Gl-Op, representing a base-line of the brain-case. Pe, Pithecanthropus. Papua, a New Guinea native. Hl, Sm, At are from skulls of monkeys. (After Dubois.)

Professor Dubois assigned the bones to one and the same skeleton, and for this he has been severely criticised. Apart from arguments affecting the geological age of the specimens, the question of their forming part of a single individual is very momentous. For if two skeletons are represented, one may be human, while the other is that of an ape. It is admitted that the larger bones were separated by a distance of forty-six feet. By way of meeting this criticism, it is submitted that the distance is by no means so great as to preclude the possibility of the common and identical origin of the various bones. Moreover it is at least curious that if two skeletons are here represented, no further remains should have been detected in the immediate vicinity.

The fact that the thigh-bone might easily have passed as that of a man, while the skull-fragment is so divergent from all modern forms as to be scarcely human, is of great interest. The contrast between the indications provided by the two bones was remarked at once. Some writers, rejecting certain other evidence on the point, then drew the inference that the human thigh-bone had been evolved and had arrived at the distinctive human condition in advance of the skull. The importance of this conclusion lies in the fact that the human thigh-bone bears indications of an erect attitude, while the form of the skull gives guidance as to the size of the brain, and consequently to some extent provides a clue to the mental endowment of the individual. Whether the erect attitude or the characteristic brain-development was first obtained by man has been debated for many years. In this case, the evidence was taken to shew that the assumption of the erect attitude came as a means of surmounting the crux of the situation. Thenceforth the upper limb was emancipated entirely from its locomotor functions. Upon this emancipation followed the liberation of jaws and mouth from their use as organs of prehension. Simultaneously the mechanism whereby the head is attached to the neck and trunk became profoundly modified. This alteration gave to the brain an opportunity of growth and increase previously denied, but now seized, with the consequent accession of intellectual activity so characteristic of the Hominidae.

The story thus expounded is attractive from several points of view. But while possessing the support of the Javan fossil remains, it is not confirmed in the embryonic history of Man, for there the growth of the brain is by far the most distinctive feature. Nor did those who adopted this opinion (in 1896), take into account all the characters of the ancient human remains even then available. For the evidence of those remains points to an order exactly the reverse of that just stated, and it indicates the early acquisition of a large and presumably active brain. And now that additions have been lately made to those older remains (other than the Javan bones), the same 'reversed' order seems to be confirmed. On the whole therefore, the soundest conclusion is that following a preliminary increment of brain-material, the erect attitude came as a further evolutionary advance.

But to return from this digression to the objections against the Pithecanthropus erectus, it must now be explained that the very contrast between the thigh-bone and the skull-cap in respect of these inferences, has been used as an argument against the association of these bones as part of one skeleton.

The objection may be met in two ways at least. For instance, the thigh-bone may yet possess characters which lessen its resemblance to those of recent men, but are not recognised on a superficial inspection. Careful investigation of the thigh-bone seems to shew that such indeed is the case (indeed the human characters are by some absolutely denied). But together with this result comes the discovery that the characters of straightness and slenderness in the shaft of the bone from which the inference as to the erect attitude was largely drawn, do not give trustworthy evidence upon this point. In fact, a human thigh-bone may be much less straight and less slender than that of arboreal animals such as the Gibbon, the Cebus monkey, or the Lemurs (especially Nycticebus). The famous Eppelsheim femur is straighter than, and as slender as that of Pithecanthropus. It was regarded at first as that of a young woman, but is now ascribed to an anthropoid ape. And in fact, even if the skull-cap and thigh-bone of Pithecanthropus should be retained in association, it seems that the title 'erectus' is not fully justified.

Another method of rebutting the objection is based on the suggestion that Pithecanthropus is not a human ancestor in the direct line. Thus to describe an uncle as a parent is an error not uncommon in palaeontology, and it was treated leniently by Huxley. To my mind this position can be adopted without materially depreciating the value of the evidence yielded by the conjoint remains, provided only that their original association be acknowledged. Should this assumption be granted, the claims put forward on behalf of his discovery by Professor Dubois seem to be justified. On the other hand, should the association of skull-cap and thigh-bone be rejected, the former has not lost all claim to the same position. For the most recent researches of Professor Schwalbe[3] of Strassburg, and the further elaboration of these by Professor Berry[4] and Mr Cross[5] of Melbourne, support Professor Dubois' view. And though the objections may not have been finally disposed of, a review of the literature called forth by Professor Dubois' publications will shew a slight margin of evidence for, rather than against his view.

The Heidelberg or Mauer Jaw[6].

Professor Dubois' Javanese researches were carried out in the years 1891 and 1892. Fifteen years separate the discovery of the Pithecanthropus erectus from that of the second great find mentioned in the introductory paragraph of this chapter. This period was by no means barren in respect of other additions to the list of human fossils. But the other results (including even the finds at Taubach) are regarded as of subsidiary importance, so that their consideration will be deferred for the present. In 1907 a lower jaw, known now as the Heidelberg or Mauer jaw, was discovered by workmen in the sand-pit of Mauer near Heidelberg.

The Mauer jaw is indeed a most remarkable specimen. The first general outcome of an inspection of the photographs or of the excellent casts (which may now be seen in many museums) is a profound impression of its enormous strength (Figs. 2, 13, and 15c). By every part of the specimen save one, this impression is confirmed. This massiveness, together with the complete absence of any prominence at the chin, would have caused great hesitation in regard to the pronouncement of a decision as to the probable nature of the fossil. The one paradoxical feature is the relatively small size of the teeth. All of these have been preserved, though on the left side the crowns of four have been removed by accident in the process of clearing away some adherent earth and pebbles. The net result shews that the teeth are actually within the range of variation provided by human beings of races still extant, though commonly regarded as 'primitive,' if not pithecoid (such as the aboriginal race of Australia). Yet these teeth are implanted in a jaw of such size and strength as render difficult the reference of the specimen to a human being.

Fig. 2. A outline tracing of a cast of the Mauer Jawbone. B a similar tracing from an unusually large jaw of an ancient Briton. (From specimens in the Cambridge Museum.)

The most striking features of the Mauer jaw have been mentioned already. Before entering upon a further discussion of its probable nature, it will be well to note some of the other distinctive characters. Thus the portion Fig. 2 (a) known technically as the ascending ramus is of great size, and particularly wide, surpassing all known human specimens in this respect. The upper margin of this part is very slightly excavated, a slight depression (b) replacing the very definite 'sigmoid' notch found in almost all human jaws (though the relative shallowness of this notch has been long recognised as distinctive of the lowest human types). The difference in vertical height between the uppermost points of the condyle (c) and the coronoid process (d) is therefore unusually small. On the other hand, the lower margin of the bone is undulating, so that it presents a hollow on each side, as well as one near the middle line in front. The two halves of the bone are definitely inclined to one another and this convergence is faintly marked in the two rows of teeth behind the canines. The latter teeth do not project markedly above the level of those adjacent to them. The incisor teeth are remarkably curved in their long axes, with a convexity in front. The prominences called 'genial tubercles' behind the chin are replaced by a shallow pit or fossa.

In one sense the reception accorded by palaeontologists to the fossil jaw of Mauer differs remarkably from most of the comparable instances. That difference consists in the comparative absence of controversy excited by its discovery. This must not be ascribed to any lack of ardour on the part of archaeologists. More probable is it that with the lapse of time, the acceptance of an evolutionary interpretation of the origin of man has gained a wider circle of adherents, so that the claims of even so sensational a specimen as this, are sifted and investigated with a judicial calm much more appropriate and certainly more dignified than the fierce outbursts occasioned by some of the earlier discoveries.

It remains to institute brief anatomical comparisons between the Mauer jaw and those of the highest apes on the one hand, and of the most primitive of human beings on the other.

(a) Of the three larger anthropoid apes available for comparison, it is hard to say which presents the closest similarity. The Gibbons do not appear to approach so nearly as these larger forms. Among the latter, no small range of individual variations occurs. My own comparisons shew that of the material at my disposal the mandible of an Orang-utan comes nearest to the Mauer jaw. But other mandibles of the same kind of ape (Orang-utan) are very different. The chief difficulty in assigning the possessor of the Mauer jaw to a pithecoid stock has been mentioned already. It consists in the inadequate size of the teeth. In addition to this, other evidence comes from the results of an examination of the grinding surfaces (crowns) of the molar teeth. These resemble teeth of the more primitive human types rather than those of apes. Finally the convergence of the two rows when traced towards the canine or eye-tooth of each side, points in the same direction.

(b) If the apes be thus rejected, the next question is, Would the Mauer jaw be appropriate to such a cranium as that of Pithecanthropus? I believe an affirmative answer is justifiable. It is true that an excellent authority (Keith[7]) hesitates on the ground that the mandible seems too massive for the skull, though the same writer recognises that, in regard to the teeth, the comparison is apt. This is a difficult point. For instance the H. moust. hauseri (cf. Chapter II) has a mandible which is far 'lower' than the capacity of the brain-case would lead one to expect. Therefore it seems that the degree of correlation between mandible and capacity is small, and to predict the size of the brain from evidence given by the jaw is not always safe. It is to be remembered that special stress was laid by Professor Dubois (cf. p. 4) on the fact that the teeth of Pithecanthropus when compared with the skull-cap are inadequately small, if judged by the ape-standard of proportion. The characters of the teeth, in so far as upper and lower molars can be compared, present no obstacle to such an association, and in fact provide some additional evidence in its favour. The crucial point seems therefore to be the massiveness of the jaw. With regard to this, the following remarks may be made. First, that the skull-cap of Pithecanthropus is on all sides admitted to shew provision for powerful jaw-muscles. And further, in respect of actual measurements, the comparison of the transverse width of the Javanese skull-cap with that of the Mauer jaw is instructive. For the skull-cap measures 130 mm. in extreme width, the jaw 130 mm. The association of the two does not, in my opinion, make an extravagant demand on the variability in size of either part. A curious comparison may be instituted between the Mauer jaw and the corresponding bone as represented by Professor Manouvrier (cf. Dubois[8], 1896) in an attempted reconstruction of the whole skull of Pithecanthropus. Professor Manouvrier's forecast of the jaw differs from the Mauer specimen chiefly in regard to the size of the teeth, and the stoutness of the ascending ramus. The teeth are larger and the ascending ramus is more slender in the reconstruction than in the Mauer specimen.

(c) Passing from the consideration of Pithecanthropus to that of human beings, the general results of the comparisons that can be made will shew that the gap separating the jaw of Mauer from all modern human representatives is filled by human jaws of great prehistoric antiquity.

The progress of an evolutionary development is accordingly well-illustrated by these specimens. And although Homo heidelbergensis is seen to be separated from his modern successors by great differences in form as well as a vast lapse of time, still the intervening period does provide intermediate forms to bridge the gulf. Not the least interesting of many reflections conjured up by the Mauer jaw, is that this extraordinary form should be met with in a latitude so far north of that corresponding to the Javanese discoveries. This difference, together with that of longitude, suggests an immense range of distribution of these ancestral types. Some of their successors are considered in the next chapter.