640 



ECOLOGY AND EVOLUTION 



minal traits (pp. 632, 663, 686, 691, 693), 

 and that adaptive human social evolution 

 has occurred and will continue to be char- 

 acteristic of future social progress. There is 

 already some tendency for man to act for 

 the benefit of unborn generations, action 

 that has been considered invalid or mean- 

 ingless by some (pp. 692, 693), but which 

 has a sound basis in the evolutionary 

 dynamics of population systems. 



In conclusion, we question the existence 

 of any innate evolutionary trend leading to 

 the "senescence" or the extinction of a spe- 

 cies. Slight genetic momentum is admis- 

 sible, but is insuflRcient to explain ortho- 

 genesis as reported for paleontological se- 

 quences. Pseudo-orthogenesis through allo- 

 metric relations of characters, and ortho- 

 selection, explain the valid examples of 

 linear evolutionary trends. Survival under 

 conditions that are repeated because of 

 the order and periodicity of natural phe- 

 nomena allows the cumulative develop- 

 ment of genetic adaptations. Conditioned 

 behavior is also dependent upon repeated 

 events. Teleological aspects of adaptation 

 may be explained through the action of 

 natural selection upon temporal population 

 systems. 



SUMMARY 



Living organisms universally exhibit ad- 

 aptation. Ecologists are particularly con- 

 cerned with exoadaptation, and physiolo- 

 gists with endoadaptation, but the two as- 

 pects of adaptation are fundamentally simi- 

 lar and have similar causations. 



Adaptation is almost always complex, 

 combining many biological mechanisms 



within an integrated pattern. Perfection of 

 adaptation is not to be expected. Complex 

 adjustments to complex factors invariably 

 involve compromise solutions. Any single 

 measurement of adaptation results in an 

 oversimplification of the concept. The com- 

 bination of adaptations within a single spe- 

 cies to a variety of factors in the habitat is 

 commonly associated with a long evolu- 

 tionary history in the particular habitat. 



It is necessary for the organism to be ad- 

 justed not only to the average conditions, 

 but also to the rare extreme environmental 

 fluctuations. Ontogenetic adjustment to the 

 whole environment of the temporal individ- 

 ual is the rule. 



In certain instances it can be shown 

 that an integrated population may exhibit 

 group adaptations similar in principle to 

 individual adaptations. 



Ancient adaptations to different environ- 

 ments become so fixed in the heredity that 

 they may linger in part as functionless 

 vestigial characters in an organism. Allo- 

 metric characters explain a few phyloge- 

 netic sequences formerly included under or- 

 thogenesis. Selection may sort variations of 

 one character physiologically associated 

 with other characters and thus pro- 

 duce pseudo-orthogenesis. Racial senes- 

 cence needs further verification before ac- 

 ceptance. 



The repetition of past conditions is neces- 

 sary for the cumulative eflFect of both ger- 

 minal selection and learned behavior, and 

 hence makes it possible for organisms un- 

 consciously or consciously to "anticipate" 

 and adjust to the future. 



34. NATURAL SELECTION 



INTRODUCTION 



The principle of natural selection, together 

 with its bearing upon progressive evolu- 

 tion, the origin of adaptation, and an under- 

 standing of man in his social setting, is 

 possibly "the most important abstract bio- 

 logical principle ever enunciated" (Pearl, 

 1930a). 



The essential concepts underlying the 

 theory of natural selection (variation, 

 heredity, overproduction, struggle for ex- 

 istence, differential survival) have been 

 checked, rechecked, analyzed, and modified 



in special details since the day of Darwin. 

 Controversy, both scientific and philosophi- 

 cal (p. 656), has raged and still rages over 

 the theory as a whole and many of its parts. 

 Darwin (1859) did not always distin- 

 guish between heritable and nonheritable 

 variation. He had no understanding of 

 hereditary mechanisms. The concept of 

 competition, which grew from considera- 

 tion of the facts of overproduction, has 

 been investigated since Darwin's day and 

 has also often been misapplied in recent 

 years. The importance of its implications 



