568 ANNUAL KEPOET SMITHSONIAN INSTITUTION, 1912. 



which we have been examining in the lowlier members of the primate 

 series. It was not the adoption of the erect attitude or the invention 

 of articulate language that made man from an ape, but the gradual 

 perfecting of the brain and the slow upbuilding of the mental struc- 

 ture, of which erectness of carriage and speech are some of the inci- 

 dental manifestations. 



The abiUty to perform skilled movements is conducive to a marked 

 enrichment of the mind's structure and the high development of the 

 neopallium, which is the material expression of that enrichment. 

 There are several reasons why this should be so. The mere process 

 of learning to execute any act of skill necessarily involves the culti- 

 vation, not only of the muscles which produce the movement, and 

 the cortical area which excites the actions of these muscles, but in 

 even greater measure the sensory mechanisms in the neopallium 

 which are receiving impressions 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 enrich- 

 ing the mental structure with new elements of experience. Out of 

 the experience gained in constantly performing acts of skill the 

 knowledge of cause and effect is eventually acquired. Thus the high 

 specialization 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 occurring 

 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 con- 

 duct in anticipation of results. 



Long ages ago, possibly in the Miocene, the ancestors common to 

 man, the gorilla, and the chimpanzee 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 distinctively primate process of gi'owth 

 and speciahzation of the brain, which had been going on in their 

 ancestors for many thousands, even millions, of years, reached a 

 stage when the more venturesome members of the group, stimulated 

 perhaps by some local failure of the customary food, or maybe led 

 forth b}' a curiosity bred of their growing realization of the possibili- 

 ties of the unknown world beyond the trees which hitherto had been 

 their home, were impelled to issue forth from their forests, and seek 

 new sources of food and new surroundings on hill and plain, wherever 

 they could obtain the sustenance they needed. The other gi-oup, 

 perhaps because they happened to be more favorably situated or 

 attuned to their surroundings, living in a land of plenty which encour- 

 aged indolence in habit and stagnation of effort and growth, were 

 free from this glorious unrest, and remained apes, continuing to lead 



