though not necessarily sprung of a single pair, he must have had, in homely language, a single cradle-land, from which the peopling of the earth was brought about by migration, not by independent developments from different species in so many independent geographical areas.

It follows further, and this point is all-important, that, since the world was peopled by pleistocene man, it was peopled by a generalised proto-human form, prior to all later racial differences. The existing groups, according to this hypothesis, have developed in different areas independently and divergently by continuous adaptation to their several environments. If they still constitute mere varieties, and not distinct species, the reason is because all come of like pleistocene ancestry, while the divergences have been confined to relatively narrow limits, that is, not wide enough to be regarded zoologically as specific differences.

The battle between monogenists and polygenists cannot be decided until more facts are at our disposal, and much will doubtless be said on both sides for some time to come[2]. Among the views of human origins brought forward in recent years should be mentioned the daring theory of Klaatsch[3]. Recognising two distinct human types, Neandertal and Aurignac (see pp. 8, 9 below), and two distinct anthropoid types, gorilla and orang-utan, he derives Neandertal man and African gorilla from one common ancestor, and Aurignac man and Asiatic orang-utan from another. Though anatomists, especially those conversant with anthropoid structure[4], are not able to accept this view, they admit that many difficulties may be solved by the recognition of more than one primordial stock of human ancestors[5]. The questions of adaptation to climate and environment[6], the possibilities of degeneracy, the varying degrees of physiological activity, of successful mutations, the effects of crossing and all the complicated problems of heredity are involved in the discussion, and it must be acknowledged that our information concerning all of these is entirely inadequate.

Nevertheless all speculations on the subject are not based merely on hypotheses, and three discoveries of late years have provided solid facts for the working out of the problem.

These discoveries were the remains of Pithecanthropus erectus[7] in Java, in 1892, of the Mauer jaw[8], near Heidelberg, in 1907, and of the Piltdown skull[9] in Sussex in 1912. Although the Mauer jaw was accepted without hesitation, the controversy concerning the correct interpretation of the Javan fossils has been raging for more than twenty years and shows no sign of abating, while Eoanthropus Dawsoni is too recent an intruder into the arena to be fairly dealt with at present. Certain facts however stand out clearly. In late pliocene or early pleistocene times certain early ancestral forms were already in existence which can scarcely be excluded from the Hominidae. In range they were as widely distributed as Java in the east to Heidelberg and Sussex in the west, and in spite of divergence in type a certain correlation is not impossible, even if the Piltdown specimen should finally be regarded as representing a distinct genus[10]. Each contributes facts of the utmost importance for the tracing out of the history of human evolution. Pithecanthropus raises the vexed question as to whether the erect attitude or brain development came first in the story. The conjunction of pre-human braincase with human thighbone appeared to favour the popular view that the erect attitude was the earlier, but the evidence of embryology suggests a reverse order. And although at first the thighbone was recognised as distinctly human it seems that of late doubts have been cast on this interpretation[11], and even the claim to the title erectus is called in question. The characters of straightness and slenderness on which much stress was laid are found in exaggerated form in gibbons and lemurs. The intermediate position in respect of mental endowment (in so far as brain can be estimated by cranial capacity) is shown in the accompanying diagram in which the cranial measurements of Pithecanthropus are compared with those of a chimpanzee and prehistoric man. The teeth strengthen the evidence, for they are described as too large for a man and too small for an ape. Thus Pithecanthropus has been confidently assigned to a place in a branch of the human family tree.

POSITION OF P. ERECTUS.
(Manouvrier, Bul. Soc. d'Anthrop. 1896, p. 438.)

The Mauer jaw, the geological age of which is undisputed, also represents intermediate characters. The extraordinary strength and thickness of bone, the wide ascending ramus with shallow sigmoid notch (distinctly simian features) and the total absence of chin[12] would deny it a place among human jaws, but the teeth, which are all fortunately preserved in their sockets, are not only definitely human, but show in certain peculiarities less simian features than are to be found in the dentition of modern man[13].