HUMAN INFANCY: ITS CAUSES, SIGNIFICANCE, 

 AND THE LIMITS OF ITS PROLONGATION 



By Joseph Hershey Bair 



By a study of comparative psychology and anatomy it will be found 

 that there is a correlation between higher mental functions and the size 

 of the cerebral hemispheres of the brain. As memory, discrimination 

 and the power to learn by experience, as well as all the higher psychical 

 factors, develop in animals, so does also the size of the cerebral cortex. 

 In the primitive vertebrates the cerebrum and cerebellum do not exist 

 as separate structures. In fishes they are very small. In the halibut, 

 e. g., a fish weighing over one hundred pounds, the cerebral hemispheres 

 are no bigger than peas, not nearly as large as the optic lobes. In 

 birds and mammals the cerebrum becomes more and more conspicuous, 

 until in the higher apes the brain pushes forward. This same process 

 is continued in man until it attains its normally enormous size. The 

 size of the cortex also increases by a process of furrowing which makes 

 its area almost four times as great as if it were smooth. The higher 

 up in the series we go, the deeper and more numerous these folds become, 

 and these, too, are an index to general intelligence and mental capacity. 



In the struggle for existence, the animal favored by variation with a 

 larger and more deeply fissured brain than his fellows, is more intelli- 

 gent, and consequently abler in the struggle for existence. This animal 

 is maintained at the expense of his less intelligent fellows who do not 

 survive. Natural selection operates in the direction of increased size 

 of brain cortex. The gulf by which man is separated from the ape 

 consists in the increase of his cerebral surface. 



Psychical variations came tq be of more use to animals in the history 

 of the race than physical variations, and were seized upon and main- 

 tained. As a result the being possessing them had greater power of 

 adapting himself to the conditions of life. He was enabled by his 

 mental powers to keep, with an unchanged body, in harmony with an 

 ever-changing environment. The being that varied most rapidly 



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