Page:Popular Science Monthly Volume 46.djvu/547

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531
BRAIN DEVELOPMENT AND EVOLUTION.

another increase in number, variety, and depth, as we have seen in the case of the Bushwoman. And thus these convolutions go on pari passu with increasing manual dexterity and intelligence, multiplying, assuming more varied and complex forms and greater depth, until we reach the most thoughtful and learned members of the highest civilized communities, where the brain surface if smoothed out would measure, on an average, about four square feet.

What immediately concerns us, however, in this connection, is the fact that not only the savage and the primitive man, but the ape and even certain quadrumana, have already found more contriving, thinking, remembering, and other kinds of brain work to do than a head and cranial capacity in due proportion to their bodies will admit of. And thus each and all are preserving and perpetuating by natural selection and heredity all the variations of increased cerebral surface resulting from more numerous, varied, and deeper convolutions.

Is it inconsistent, then, with the theory of evolutionary descent for the savage to have the largest possible cranial capacity and head not out of due and advantageous proportion to his body and the demands of his mode of life? This question is completely answered by the fact, which has now been fully set forth, that the further growth of head and consequent cranial capacity in his case has been already arrested, as in the case of the ape and the quadrumana, at the point of becoming too large for his body and mode of life, while his still increasing and developing mental and emotional powers and activities have already found a substitute for further cranial capacity, or head growth, in more numerous, complex, and deeper convolutions, thus increasing the brain surface.

It is surprising that this objection has not been earlier demurred to on the specific ground of inadequacy. It now appears that as well might the cranial capacity of an ape as that of a savage or a primitive man be made the basis of this objection, since in all three cases further head growth has been checked at the point of undue proportion to the body, and thereafter increasing mental activity has found a physical substitute for further head or brain growth in the preservation, as a fitter adaptation, of every fortuitous variation in the direction of these increased convolutions, first foreshadowed in the quadrumana, reaching the highest complexity in civilized man, and co-ordinated to advancing intelligence at every intermediate step.

Thus we see that this popular objection crumbles at the first touch of a few simple and well-known facts.