CHARACTER EVOLUTION 



239 



the habitat in which they find their food. Similarly there 

 arises a more or less close analogy between the motor organs of 

 all the mammals living in any particular habitat; thus the glis- 

 sant or volplaning limbs of all aero-arboreal types are exter- 

 nally similar, irrespective of the ancestral orders from which 



HABITAT CHANGE ACCOMPANYING CHANGE OF FUNCTION 



motor adaptations of different animals to similar life zones 

 Fig. 115. Adaptive Radiation of the Mammals. 



The mammals, probably originating in arboreal leaping or climbing phases, radiate 

 aclaptively into all the other habitat zones and thus acquire many types of body form 

 and of locomotion more or less convergent and analogous to those previously evolved 

 among the reptiles (shown in the right-hand column), the amphibians, and the fishes. 

 Diagram by Osborn and Clregory. 



they are derived. A mammal may seek any one of twelve 

 different habitat zones in search of the same general kind of 

 food; conversely, a mammal living in a single habitat zone 

 may seek within it six entirely different kinds of food. 



This principle of the independent adaptation of each organ 

 of the body to its own particular function is in keeping with 

 the heredity law of individual and separate evolution of "char- 

 acters" and "character complexes" (p. 147), and is fatal to 



