Pleistocene Man.
Pithecanthropus erectus.
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.)
Mauer jaw. Homo Heidelbergensis.
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].
GENEALOGICAL TREE OF MAN'S ANCESTRY.
(A. Keith, The Antiquity of Man, 1915; fig. 187, p. 501.)