Page:Popular Science Monthly Volume 46.djvu/545

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BRAIN DEVELOPMENT AND EVOLUTION.

which the brain surface is increased, do furnish a better index. Second, that this physical co-ordination with increased mental and emotional activity, this physical manifestation of developing mind, has already taken place in the brains of apes, and is foreshadowed in the lower species of quadrumana.[1] Furthermore, from an intelligent standpoint this is precisely what might have been expected.

Let us bear in mind that out of all the innumerable, almost infinite number of variations, eccentricities, and oddities, however slight, found by examining each individual microscopically (if such a thing were possible), those minute changes and peculiarities, and those only, will be preserved in the long run, and after many generations, which are of such a character as to secure for their possessors more vigor and longevity than those without them can possibly have, simply because vigor and longevity vastly increase the opportunities of heredity.

Now the size and weight of the brain in proportion to the size and weight of the body is just one of those important proportions of parts which would make for or against the vigor and long life of the individual in a marked degree. One other concurrent condition, however, would perhaps be of even greater importance, and it is this: that the height, size, form, and weight of the whole body should have the fittest adaptation to its circumstances and to the work required of it, in order to secure the greatest vigor and longest life, and so at last to become the characteristic of every member of the species. So it is plain that the brain as to size and weight must stand two tests. It must not only bear the best possible proportion to the body, but that body must be of the fittest size and weight to meet successfully, and for the longest period, all that it is compelled to encounter, and thus to succeed above all other less fortunate individuals in finally making this double due proportion the property and the universal characteristic of the species. Within these limitations and conditions, but not otherwise, the size and weight of the brain and consequent cranial capacity are doubtless subject to the amount of mental instinctive, receptive and emotional activity demanded of it, and carried on within it. In shorter phrase,


  1. Functions of the Brain, by David Terrier, M. D., F. R. S., Professor of Forensic Medicine, King's College, London, published by Smith, Elder & Co., 51 Waterloo Place, London, p. 297: "The brain of man is constructed on the same type as that of the monkey, and essentially the same primary fissures and convolutions are recognizable in both, the chief differences consisting in the greater complexity of the convolutional arrangement of the human brain, caused by the development of the numerous secondary and tertiary gyri, which tend to obscure the simple type of the simian brain. These differences are more marked in the adult and highly developed brain, but are less pronounced in the fœtal human brain." See, also, Ecker on the Convolutions of the Human Brain, translated by Gallon, etc.