120 HUMAN BIOLOGY 



Among existing classes of primate new senses have not 

 appeared, but the distance senses of hearing and sight have 

 greatly increased in complexity and in perceptual value. 

 Replacing to a marked degree the mechanical and chemical 

 senses, they have become the dominant channels of com- 

 munication between the primate and its world. The degree 

 of dominance of visual and auditory receptivity and percep- 

 tion increases from lemur to man. 



PREEMINENTLY IMPORTANT ASPECTS OF BEHAVIORAL 



ADAPTATION 



An animal adapts psychobiologically to its world as 

 known. If its knowledge be hmited to simple awareness, 

 through contact, chemical action, vibrations in air or ether, 

 of the existence of media about it and of objects and occur- 

 rences in those media, it cannot adapt as do monkeys, 

 apes and men. There must be perceptual acquaintance 

 with objects in relation. An animal obviously cannot respond 

 to an apple as a spherical form of definite size, distance 

 from the perceiver, texture and color, if it is sensed merely 

 as a dark spot against a lighter background. Perceptual 

 configurations are definitely known to become more numer- 

 ous, complex, and useful as bases for adaptive behavior 

 from conception to maturity in human life and from lemur 

 to man in the phylogenetic series. We may not trace the 

 progress step by step in either case, but the trend toward 

 increasing richness and efficiency of perceptual consciousness 

 is wholly apparent. 



In still another way than through the guiding awareness 

 of the presence, qualities, and relations of objects and events, 

 perceptual consciousness conditions adaptive ability. It is a 

 basis of motivation. An animal strives for objectives only 

 within the limits of its consciousness. There is a stage in 

 human development, as there are stages in evolution, when 

 neither the quantity nor the quality of an objective clearly 

 influences the organism. The less preferred object tends to 

 induce the same response as the more preferred; a small 

 bit of candy or fruit tends to induce as strenuous effort to 

 obtain it as does a large bit. We say there is lack^of dis- 



