Variations and Adaptations in Animals and Plants. 729 



(cacti) and some are able to live in swampy areas (cattails, etc.), while 

 others are able to live in the frigid regions of the poles or on mountain 

 tops (certain mosses, shrubby plants, etc.). An organism may be ren- 

 dered unfit for a particular environment because of the presence of 

 certain variations and their attendant adaptations, while that same 

 organism with its same traits might fit perfectly into a different environ- 

 ment. Successful living depends upon the mutual fitting in of inherent 

 abilities and the surrounding environment. An adaptation may be 

 regarded as the result of developmental changes resulting from inherita- 

 ble variations, with the retention of those which are advantageous. Un- 

 desirable variations may have resulted in the destruction of other or- 

 ganisms through the "struggle for existence" in the process of natural 

 selection. 



Motile organisms may be able to move into an environment which may 

 prove to be more satisfactory for their particular abilities. The assump- 

 tion is that the degree of adaptability to an environment or the ability 

 to seek and find a more desirable environment commensurate with its 

 abilities is an influential factor in the successful struggle for existence. 



Adaptations may be divergent (L. diver gere, to incline away) or con- 

 vergent (L. convergere, to incline together). In divergence (adaptive 

 radiation), species of living organisms that are somewhat closely related 

 tend to radiate in various directions into diflferent environments and be- 

 come modified accordingly. From the standpoint of locomotion, the 

 various species of mammals have become adapted to live on land (walk- 

 ing and jumping), in the ground (digging), in water (swimming), in 

 trees (hanging), and in the air (flying). In co7ivergence (parallelism), 

 species of organisms belonging to different orders, families, etc., tend to 

 become adapted to the same type of environment by means of similar 

 modifications. For example, the wings of bats and flying squirrels are 

 adapted for flying, the forelimbs of badgers and ant eaters for digging, 

 the forelimbs of seals and porpoises for swimming, the limbs of sloths 

 and gibbons for hanging, etc. In convergent (parallel) evolution there 

 is a development of similar traits or features along similar lines among 

 unrelated, or distantly related, groups of organisms. An example of con- 

 vergent evolution among members of widely separated (distantly related) 

 families of plants growing in similar environments is the development in 

 desert-inhabiting cacti, spurge, live-for-ever, etc., of such similar char- 

 acters as reduction or complete absence of leaves, formation of heavy 

 layers of protective cutin, production of spines, and development of water 

 storas^e tissues. 



