THE PROGRESSION OF LIFE ON EARTH
apes, they must be regarded as the ancestors of both the modern apes and man. Not all the stages between the ape and man have yet been found, because the higher the brain power the more wary the animals would become in avoiding accidents by which their remains could be buried in the earth; but the few fragments that are known show that the links certainly existed. The teeth and jaws of fossil apes suggest that they belonged to animals which may have been ancestral to man as well as to modern apes, and the oldest known fossil human skulls and jaws exhibit more ape characters than any human skull and jaw of the present day.
The oldest jaws of apes thus far discovered are from the early Tertiary (Oligocene) deposits of Egypt and belong to animals smaller even than the existing gibbons, the smallest living apes. They have a short, bony chin and small canine teeth. By a very slight reduction of the canine teeth and equally slight changes in the molar teeth the heads of these apes would approach in form the modern human head. By an enlargement of the canine teeth and a lengthening of the bony chin they would acquire the jaw of an existing ape.
The jaws of the next higher apes, from the middle Tertiary (Upper Miocene and Lower Pliocene) of Europe, represent larger animals, equalling in size a modern chimpanzee. The so-called "forest-ape" (Dryopithecus) now has powerful canine teeth, and so is approaching the modern apes rather than man; but its molar teeth are remarkably human in appearance, and the short, bony chin was less prominent than that of the chimpanzee and gorilla.
Teeth and fragments of jaws of several other apes from rocks of the same age in India show that in this region there must have been more variety among apes than is seen anywhere at the present day. There is, in fact, good reason for supposing that these animals may have included some of the
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