mode of locomotion in harmony with an adaptation instinctively and organically fixed.
One hypothesis among others would be the destruction, more or less complete, of the forests on an island inhabited by anthropoids capable of taking, when necessary, the biped attitude. The ancient volcanoes of Java might have accomplished this destruction and have rendered necessary the adaptation to the upright position under pain of extinction of the race.
It would be impossible to explain easily the disappearance of an anthropomorphous species as much superior to all others as was that of the individual from Trinil; for it was strongly built with a cerebrum superior to all known species of the order of Primates. It possessed, then, excellent chances of survival in the struggle for life. But, on the hypothesis here considered, the species Pithecanthropus erectus would not have disappeared. Having become a human race, it could not remain at the same time a race anthropoid. If the Pithecanthropus was only a simple precursor, it was superior enough to the other animals to survive unless the human species, springing up all of a sudden, "from the clay of the earth," did not hasten to annihilate this dangerous competitor. But if the Pithecanthropus was an ancestor, its species lives yet in its human descendants.
The difference between the Pithecanthropus and existing man is so small that there is no call to search for an intermediate link. The link is sufficiently represented by the lowest of our savage races; for example, the isolated human skulls, Australian and others, that have already been shown to be very little different in many respects from that of Trinil.
Supposing that among several species of gibbon, Gx, Gy, Gz; this latter species evolved toward the human type and became finally, in assuming the upright position, the Pithecanthropus erectus=H1, then that it, by virtue of the multiple consequences of the upright position, became progressively H2, a stage corresponding to the lowest existing races, we obtain in simplifying:
Gibbon x
Gibbon y
Gibbon z—H0—(P.E.=H1)—H2.
There ought to be then in the existing fauna a hiatus formed by the transformation of the gibbon z into H0, then of H0 into H1, so that, in this existing fauna, the species nearest to H2 ought to be a species very inferior, issue of gibbon x or y. The gap here ought to be all the greater in that it is not only a question of a transformation such as that of one quadruped into another, conserving the generic characters of its ancestor;
