Page:Popular Science Monthly Volume 60.djvu/373

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THE DESCENT OF MAN.

THE DESCENT OF MAN.
By Professor LINDLEY M. KEASBEY,

BRYN MAWR COLLEGE.

GENERAL evolutionary evidence led anthropologists some time ago to postulate a pliocene precursor of man, but their surmise has only recently been substantiated by particular proof. The search for the so-called missing link was at first confined to the temperate zone. Many discoveries were made, but, as the skulls and implements unearthed were all taken from pleistocene deposits, there was nothing to indicate the existence of man on earth before quaternary times. It was not, indeed, until investigations were transferred to the tropics that earlier vestiges of human life were revealed. In the year 1894 Dr. Eugene Dubois discovered the upper portion of a stall and some skeletal parts of a distinctly human creature buried in the pliocene beds of East Java. These remains have since been subjected to the strictest scientific scrutiny and pronounced genuine. Taking the geological location of the discovery into account, there can be no further doubt, therefore, that in this tropical region the human species was already differentiated from the apes in tertiary times.

Judging from the size and form of the skull, and from such portions of the skeleton as remain, the variation of the human prototype, or to give him his scientific name. Pithecanthropus erectus, was evidently along both psychic and physical lines; the former showing a difference of degree, the latter exhibiting a distinction in kind.

There are two anatomical tests of intellectual superiority: cranial capacity and the convolutions of the brain, both of which can be applied in the present instance. It is a well-known fact that the frontal bone, which forms the vault of the anterior part of the cranium of young men and apes, is divided by a suture. So long as this line of growth remains open, the fore part of the cranium can expand; but if the anterior. sutures of the skull consolidate early in life, the cranium cannot increase in capacity beyond the size reached in early infancy. In consequence of the early closure of these sutures in the anthropoid apes, the cranial capacity of these creatures is restricted, and the fore part of their brain rarely increases beyond the size attained at the end of the first year of life. With man, however, these sutures do not consolidate until a much later period, and, as the anterior lobes of the brain continue to develop, human cranial capacity increases accordingly. As a result, the average human being possesses four times as