CHAPTER V 



Adaptation Difficulty of explaining by the mutation theory Examples of adap- 

 tation Protective coloration Seasonal changes Imitative adaptation 

 Pitcher-plants Drosera The Yucca and the moth Pronuba Parasitic 

 adaptation The material provided by variation for natural selection to 

 work upon The biometrical principle Conclusions. 



THERE is a phenomenon in nature, so striking and so general, 

 that no theory of evolution can be accepted as plausible, or 

 even possible, which fails to explain it. This is the extra- 

 ordinary adaptation of living organisms to their surroundings. 

 Not only are they adapted to their physical conditions, but 

 above all, to each other. The mutation hypothesis not only 

 fails to explain this, 1 but a careful consideration of its postulates 

 shows, that the co-adaptation of living organisms to each 

 other and to their environment, and the origin of species by 

 mutations, are incompatible. The only means of escaping 

 from this conclusion would be by assuming (1) that a 

 mutation takes place first, and the adaptation afterwards, 

 through the accumulation of fluctuating variations, the 

 organism surviving during this process, although it is out 

 of harmony with its environment ; or (2) that adaptation 

 has been arrived at by just as great a number of minute 

 mutations as Darwin and Wallace assumed of fluctuating 

 variations for the same process. 



There is no living organism which would not serve as 

 an example of the phenomenon of adaptation. We must, 

 however, consider a few individual cases in order to realise 

 its full significance. 



Sitaris humeralis, a beetle belonging to the family 



1 This has been admitted by the mutationists themselves, e.g. Bateson, W. : 

 " Nor have we any definite light on the problem of adaptation . . .'' (Report 

 of Uritish Association, Cambridge Meeting, p. 587, 1904). 



77 



