808 Comparative Morphology of Chordates 



tool. The movements of the hand were determined by motor impulses 

 originating in a central nervous system whose brain had received, via 

 the optic nerves, sensory impulses derived from a retinal image of a 

 mammoth. Presumably the drawing was made from a stored mental 

 image. It is not likely that the mammoth stood by and posed for the 

 picture. It is not reasonable to regard the act of drawing as instinctive 

 or automatic. Many other mammals possessing a well-developed 

 cerebral cortex have seen elephants but have never made pictures of 

 them. That early human act was unique — something new in the history 

 of the world's life. It had no reference to physical needs of the body. 

 It reveals the emerging of faculties to which we give such names as 

 "imagination," "purpose," "constructive initiative," "intelligence." 

 In that simple act of the cave man, his tool-grasping hand guided by a 

 central nervous mechanism capable of mediating these incipient 

 faculties, may be discerned the basic factors in the further evolution 

 of the human primate. Crude vocal sounds came to be employed as 

 means of communication. Marks or lines made on smooth surfaces 

 came to signify certain objects or sounds, and so began communication 

 by writing. With the advent of machines, writing was replaced by 

 printing, but both the machine and that which it prints owe their 

 origin to the imaginative and creative faculties which find outlet via 

 the human brain. Long ages after the cave man, the hand of Michel- 

 angelo, grasping a brush and guided by an imagination transcending 

 known reality, depicted on the walls of the Sistine Chapel the creation 

 of man. Another hand, its tool a pen, traced the lines of Shakespeare's 

 plays ; another set down the notes of Beethoven's symphonies. 



The primate line of specialization involves primarily the hand and 

 the brain. Creative and adaptive modification of the environment 

 exempts the remainder of the body from any urgent need of changing 

 (which must not be construed as implying that evolutionary change 

 takes place in response to need). Locomotor mechanisms enable man 

 to transport himself on all three of the earth's habitable levels — water, 

 land, air — at a degree of speed and comfort which could not possibly 

 be attained by any anatomic modification of his body. If improved 

 sight is needed, it is provided by microscope and telescope. Range of 

 hearing is extended by telephone and radio. The human voice is 

 mechanically amplified. By use of numerous instruments, musical and 

 otherwise, a variety of sounds other than vocal may be enjoyed or 

 endured. It has accordingly been predicted that, in so far as bodily 

 functions are replaced by external mechanical and chemical means 

 (e.g., as when a meat grinder is used instead of teeth), the organs thus 

 relieved of full function will ultimately suffer regressive evolution or 

 "degeneration." This is an interesting possibility, but the prediction 



