§2 evolution: the ages and tomorrow 



spheres, which are superimposed upon the previous two re- 

 gions. Gradually, up through reptiles and mammals to man 

 these cerebral bodies take on greater and greater mass and 

 complexity until they are larger than all the rest of the 

 nervous system put together. As will be brought out later, 

 it is the invention of sensory apparatus and the improvement 

 of the vertebrate brain, as well as the organization of asso- 

 ciation areas in the cortex of the cerebral hemispheres, that 

 have led to the self -consciousness and the conceptual proc- 

 esses of man. This is progress. 



In the evolution of other structures in the vertebrates, the 

 sharks and true fishes set the pattern. The skeleton is estab- 

 lished with two girdles, shoulder and hip, and is calcified in 

 such a manner as to leave living cells within and to provide 

 for future flexibility. The amphibian (the frog and salaman- 

 der are modern examples) crawls out on land by the middle 

 of the Paleozoic era, some 500,000,000 years ago, and then 

 the land vertebrates begin their relatively rapid and very 

 spectacular evolution. Besides lungs for breathing air and 

 other internal structures, the great invention of the am- 

 phibian was the five-fingered limb. The monkeys, great 

 apes, and finally man make the greatest use of this limb. To 

 pick up objects and to observe them was, as will be shown 

 later, an important factor in the learning of the primates. It 

 set up a correlation between hand and eye that led to in- 

 creased awareness and finally to greater educability. The 

 potential flexibility of the Rve fingers of the amphibian an- 

 cestor is realized, when proper control evolves, in the piano 

 virtuosity of man. 



The reptile adds to its general amphibian structure an 

 embryonic sack called the amnion, an invention that has 

 freed the reptiles, birds, and mammals from the seasonal 

 return to water for reproduction. This sack, which is left 

 behind at birth, surrounds the embryo early in development 

 and floats it in a liquid medium with the salt concentration 

 of the seas from which the land vertebrates were derived. 



