386 



The Journal of Heredity 



why this should be so. The mere proc- 

 ess of learning to execute any act of 

 skill necessarily involves the cultivation, 

 not only of the muscles which jjroduce 

 the movement, and the cortical area 

 which excited the actions of these 

 muscles, but in even greater measure 

 the sensory mechanisms of the neopal- 

 lium which are receiving imjjressions 

 from the skin, the muscles, and the 

 eyes, to control the movements at the 

 moment, and incidentally are educating 

 these cortical areas, stimulating their 

 growth, and enriching the mental struc- 

 ture with new elements of experience. 

 Out of the experience gained in con- 

 stantly performing acts of skill the 

 knowledge of cause and effect is even- 

 tually acquired. Thus the high sj^ecial- 

 ization of the motor area, which made 

 complicated actions possible, and the 

 great expansion of the temporo-parietal 

 area, which enabled the ape-man to 

 realize the "meaning" of events occur- 

 ring around it, reacted one upon the 

 other, so that the creature came to 

 understand that a particular act would 

 entail certain consequences. In other 

 words, it gradually acquired the faculty 

 of shaping its conduct in anticii)ation 

 of results. 



MAN LEAVES THE TREES. 



Long ages ago. possibly in the 

 Miocene, the ancestors common to man, 

 the gorilla, and the chimjjanzee became 

 separated into groups, and the different 

 conditions to which they became exposed 

 after they parted company were in the 

 main responsible for the contrasts in 

 their fate. In one group the distinc- 

 tively primate process of growth and 

 specialization of the brain, which had 

 been going on in their ancestors for 

 many thousands, even millions, of years, 

 reached a stage when the more venture- 

 some mcmlxTs of the grou]), stimulated 

 perhaps by some local failure of the 

 customary food, or maybe led forth by 

 a curiosity bred of their growing realiza- 

 tion of the possibilities of the unknown 

 world beyond the trees which hitherto 

 had been their home, were im])elled to 

 issue forth from their forests, and seek 

 new sources of food and new surround- 



ings on hill and jjlain wherever they 

 could obtain the sustenance they needed. 

 The other group, j^erhaps because they 

 happened to be more favorably situated 

 or attuned to their surroundings, living 

 in a land of plenty which encouraged 

 indolence in habit and stagnation of 

 effort and growth, were free from this 

 ■ glorious unrest, and remained apes, 

 continuing to lead very much the same 

 kind of life (as gorillas and chimpanzees) 

 as their ancestors had been living since 

 the Miocene or even earlier times. That 

 both of these unenterprising relatives 

 of man happen to live in the forests of 

 tropical Africa has always seemed to me 

 to be a strong argument in favor of 

 Darwin's view that Africa was the 

 original home of the first creatures 

 definitely committed to the human 

 career; for while man was evolved 

 amidst the strife with adverse condi- 

 tions the ancestors of the gorilla and 

 chimpanzee gave up the struggle for 

 mental supremacy simply because they 

 were satisfied with their circumstances; 

 and it is more likely than not that they 

 did not change their habitat. 



The erect attitude, infinitely more 

 ancient than man himself, is not the 

 real cause of man's emergence from the 

 simian stage; but it is one of the factors 

 made use of by the expanding brain as 

 a prop still further to extend its growing 

 dominion, and by fixing and establish- 

 ing in a more decided way this erectness 

 it liberated the hand to become the 

 chief instrument of man's further prog- 

 ress. 



In learning to execute movements of 

 a degree of delicacy and precision to 

 which no ape could ever attain, and the 

 primitive ape-man could only attempt 

 once his arm was completely emanci- 

 pated from the necessity of being an 

 instrument of ])rogression, that cortical 

 area which seemed to serve for the 

 i:)henomena of attention became en- 

 hanced in importance. Hence the pre- 

 frontal region, where the activities of 

 the cortex as a whole are, as it were, 

 focused and regulated, began to grow 

 until eventually it became the most 

 distinctive characteristic of the human 

 brain, gradually filling out the front of 



