648 



ECOLOGY AND EVOLUTION 



mosomes (over 100 genes modify the eye, 

 and 140 genes modiiy the wing), and the 

 genetic complexity is certainly not limited 

 to the known mutations. 



A gene is detected only when it mutates, 

 and obviously not all the genes affecting 

 these complex adapted structures have 

 mutated in such a manner and at such 

 times as to be detected by the geneticists. 



That all the genes basic to the develop- 

 ment of an insect wing could arise simul- 

 taneously and in harmony with the pre- 

 existing genetic and embryological system 

 is statistically highly improbable, iJf not 

 fantastic, even with the long periods of 

 time involved in organic evolution (Simp- 

 son, 1944, p. 54). It is true that wings 

 seem to appear rather suddenly in the up- 

 per Pennsylvanian insects, and eyes appear 

 independently in Ordovician vertebrates 

 and Proterozoic arthropods, but the sud- 

 denness of appearance is far more easily 

 explained by the gaps in the paleontologi- 

 cal record than through macroevolution of 

 such highly adapted and genetically com- 

 plex organs. The concept of preadaptation 

 has some vaUdity, but this is pushing the 

 theory much too far. 



Sumner (1942, p. 438) quotes Darwin 

 as saying: 



"He who believes that some ancient form 

 was transformed suddenly through an internal 

 force or tendency into, for instance, one fur- 

 nished with wings, will be almost compelled 

 to assume, in opposition to all analogy, that 

 many individuals varied simultaneously . . . 

 He will further be compelled to believe that 

 many structures beautifully adapted to all the 

 other parts of the same creature and to the 

 surrounding conditions have been suddenly 

 produced; and of such complex and wonderful 

 adaptation, he will not be able to assign a 

 shadow of an explanation ... To admit all 

 this is, as it seems to me, to enter into the 

 realms of miracle, and to leave those of 

 Science." 



Ferris (1943) expresses himself even 

 more emphatically against macroevolution. 

 He points out that known intergradations 

 are at variance with the concept of macro- 

 evolution of fly mouth parts, as has been 

 postulated by Villee (see counter critique 

 by Goldschmidt, 1945a). Silow (1945) 

 shows that taxonomic divergence parallels 

 genotype differences in species of cotton 

 with no indication of macroevolution. Hux- 



ley (1942) says: "To produce adapted 

 types by chance recombination in the ab- 

 sence of selection would require a total as- 

 semblage of organisms that would more 

 than fill the universe, and overrun astro- 

 nomical time." (For an opposing interpre- 

 tation in the case of mimicry, see Gold- 

 schmidt, 1945; see also p. 670. ) 



Selection of the habitat (organic selec- 

 tion) may carry some preadaptive imphca- 

 tions; such choice of conditions may also 

 be an adaptive characteristic. Even the 

 sprouting seed has phototropic, geotropic, 

 and hydrotropic growth reactions that 

 orient the growing plant to the environ- 

 ment. Animals commonly use their powers 

 of locomotion to avoid unfavorable situa- 

 tions and to move to favorable environ- 

 ments and, once there, to maintain ecologi- 

 cal position (Kendeigh, 1945; see also p. 

 671). The capacity to react differentially 

 to the environment is often so complex in 

 terms of structure, neuromechanisms, and 

 physiology that it must be assumed that 

 gene patterns affecting the capacity for en- 

 vironmental orientation are the product of 

 long periods of selective sorting. The muta- 

 tions or recombinations that initiate selec- 

 tion of or survival in somewhat new envi- 

 ronments may be, at least in part, the re- 

 sult of simple genetic modifications with 

 chance adaptive effects. 



We may summarize our opinion of the 

 role of preadaptation in its various aspects 

 by stating that the concept has real vaUd- 

 ity; that it brings to our attention the ran- 

 dom effect of recombinations and muta- 

 tions so far as environmental adjustment is 

 concerned; that it indicates in part how the 

 organismic stage is set for further adaptive 

 evolution; that organisms, particularly ani- 

 mals, may exercise conscious or unconscious 

 choice of habitat through behavior re- 

 sponse; but that preadaptation without 

 natural selection cannot be used to explain 

 the whole or even a large proportion of 

 complex organic adaptation. 



SELECTION PRESSURE 



Natural selection is presumed to have 

 been operating indirectly upon germinal 

 patterns through organismic— especially so- 

 matic—function over long periods of time. 

 We may well examine the indications that 

 a survival of the fit and an elimination ol 

 the unfit actually occurs. 



