MENTAL EVOLUTION IN THE PRIMATES II9 



acquaints the animal only with its immediate physical 

 environment, whereas taste, smell, hearing and sight bring 

 it into relation with increasingly remote objects and events. 

 As we develop during the first few months after birth, 

 we are rapidly projected into environment, and the physical 

 self is enabled to sense and respond to, investigate and 

 adjust to, increasingly numerous and distant qualities and 

 objects of its world. 



We may not assert it as fact, but the evidences strongly 

 suggest that as our senses develop, so also have they evolved 

 in the course of racial history. Like our embryonic selves, 

 our early ancestors knew the world chiefly through contacts 

 and chemical changes. But our less remote ancestors, 

 monkey-like creatures perhaps, and our infant selves, 

 lived in a world which was enriched by innumerable sounds 

 and sights. This contrast between a world of contacts and 

 tastes and one predominantly visual and auditory transcends 

 •our present powers of psychological description. 



It is not alone by addition of senses, or even by multiplica- 

 tion of qualities within a sense mode, that development 

 and evolution proceed; a given sense may become either 

 simpler or more complex, its keenness may diminish or 

 increase during individual or racial history. Less generally 

 known is the fact that the functional significance of a sense 

 may change tremendously by reason of integrative psycho- 

 biological processes which enable the organism to perceive 

 varied aspects and relations as contrasted with simple 

 qualities of objects, and which thus prepare the way for new 

 types of behavioral adaptation. For example, in individual 

 development and in evolution vision begins with awareness 

 of light. Later the animal comes to perceive form, size, 

 texture, distance, spatial relations, color. The adult sees 

 both more and differently than the newly born infant; 

 the ape sees more and differently than the lemur, and man 

 sees vastly more than any other primate. Observation 

 indicates that the trends of receptivity in development 

 and in evolution roughly agree. This fact is peculiarly 

 significant because we may follow as exactly as we will 

 the story of development and by the results may be guided 

 in our search for phylogenetic relations. 



