632 



ECOLOGY AND EVOLUTION 



lepsy correlated with appearance during 

 predator activity. 



Harmony of endoadaptation and exo- 

 adaptation of a more subtle nature is com- 

 monly observed. After using certain fishes 

 as illustrations, Sumner (1942, pp. 435, 

 436) says: "An animal distributes its pig- 

 ment in significant patterns on the body 

 surface and develops appendages on the 

 skin, thus closely matching details of its 

 usual habitat." Moreover, "the animal ac- 

 quires a mechanism for color-change which 

 is almost coextensive with the entire organ- 

 ism, involving as it does the eyes (see p. 

 126), large parts of the nervous system, 

 highly specialized effector cells in the skin, 

 and frequently the secretions of endocrine 

 glands, and no function seems conceivable 

 except that of rendering the organism in- 

 conspicuous against backgrounds of vary- 

 ing color and pattern." 



Adaptation, either within the entire or- 

 ganism or between the organism and its 

 environment, is never perfect (Cowles, 

 1945). When one considers the large num- 

 ber of operational factors, their fluctua- 

 tions in the contemporaneous environment 

 and during geologic history, and the multi- 

 plicity of organismic needs, optimal adjust- 

 ment of each part of the complex organism 

 to each factor in the complex environment 

 would seem utterly impossible. Even the 

 simplest organisms in the simplest and 

 most stable environments would still pres- 

 ent such complex relationships that func- 

 tional compromises would be necessary. 

 The ancient adjustment of the ancestors of 

 an existing successful animal established 

 a basic plan that limits the capacity for 

 further adaptive modification. The evolu- 

 tion of the higher vertebrates from fishes 

 imposes definite restrictions on the attain- 

 ment of speed in terrestrial forms (Westoll, 

 1943; Howell, 1944). Adaptations toward 

 more optimal control of the cell environ- 

 ment attained in multicellular plants and 

 animals necessitated the loss of many 

 functions in individual cells. 



It may also be added that specialized 

 nongenetic individual fimction within a 

 highly complex insect or human society 

 (pp. 420, 686, 691, 693) is made at the 

 sacrifice of the more versatile functions of 

 the primitive nonsocial individual (Emer- 

 son, 1942). The evolution of balanced 

 equilibrium within an organism may be 



paralleled by an evolution of equilibrium 

 within a population, both necessitating 

 compromise (p. 426). 



Though there is complete gradation from 

 simple adaptation to complicated adapta- 

 tion, it seems justifiable to separate chance 

 modifications, which under certain circum- 

 stances may be of survival value and are 

 likely to be produced by simple genetic 

 factors, from adaptations that show a 

 nicety of adjustment to complex situations 

 and are likely to be the result of an intri- 

 cate genetic pattern. On the basis of 

 chance, a complete complex adaptation 

 could probably not have originated de novo 

 (p. 647). 



If an adaptation is characteristic of a 

 large taxonomic category, such as a phvlum 

 or a class, one may assume that such an 

 adjustment was more important during its 

 evolution than an adaptation characteristic 

 of an included lower category. As an ex- 

 ample, chelicerae adapted to predation 

 and ultimately also to parasitism are char- 

 acteristic of the superclass Chelicerata 

 (Arthropoda), which includes the classes 

 Palaeostraca (horseshoe crabs), Eurypter- 

 ida (sea scorpions), Pycnogonida (sea 

 spiders), and Arachnida (scorpions, har- 

 vestmen, spiders, ticks, and mites). Hence 

 it is possible to say that adjustment to pre- 

 dation preceded and is more fundamental 

 than the adjustment to terrestrial life in 

 these animals. Predation is also characteris- 

 tic of all coelenterates, althou8;h one class, 

 the Anthozoa, is bottom-dwelling, and an- 

 other class, the Scyphozoa, is pelagic in the 

 adult staee. Classes of animals that have 

 evolved around parasitic adaptations (i.e.. 

 Sporozoa. Trematoda [Fig. 249], and 

 Cestoda [Fig. 2501) are found in a wide 

 variety of ecologic habitats, but are always 

 parasites in each association. 



The evolution of exoadaptation is a pri- 

 mary problem for the ecologist. We are al- 

 ready aware that there is a chronological 

 separation between the parts of the hered- 

 itary system, and that gradual sorting 

 through selection (pp. 640, 648) is basic 

 to the pattern of a functional system as we 

 now see it in an existing organism. In the 

 study of every organism, the environment 

 is so much involved through selective elim- 

 ination that improvement of our under- 

 standing of the organismic system depends 

 not only upon knowledge of the present 



