EVOLUTION AND ADAPTATION. 



159 



EVOLUTION AND ADAPTATION * 



A Criticism. 



By Rev. Prof. G. Henslow, M.A., V.M.H., &c. 



The central idea of this book is to supersede Darwin's " Origin of Species 

 by Means of Natural Selection " among fluctuating individual differences, 

 by the Mutation-theory of De Vries. The author does not accept Darwin's 

 alternative view of the origin of species by means of " the direct action of 

 changed conditions of life," the results being " definite variations," by 

 which "a new variety will arise without the aid of natural selection." t 



In one sentence Dr. Morgan appears to recognise this possibility : " If 

 a species begins to give rise to a large number of individuals of the same 

 kind through a process of discontinuous variation, then it may happen 

 that a new form may establish itself," &c. ; otherwise the author repudiates 

 the process. 



With regard to mutations he says : " Whether an organism that 

 arises [by the survival of only those mutations that are sufficiently 

 adapted to get a foothold] shall persist, depends on whether it can find a 

 suitable environment" (p. -163). 



It is thus seen that here, as in Darwinism, there is no natural laiv, 

 correlating the appearance of the mutations or variations, respectively, 

 with the necessary environments. " Chance" reigns supreme with both 

 theories. 



The feature, therefore, common to the two theories is that the new 

 variations or mutations arise independently of the conditions of life best 

 suited to them. With Darwin the variability + is stimulated by the 

 latter ; but not with De Vries, by whom the stimulation is supposed to 

 come from within, so that the mutation has to find a suitable environ- 

 ment or die. 



An example will illustrate the author's contention. Darwin con- 

 sidered the loss of flight in domesticated ducks and fowls to be due to 

 disuse, and the drooping ears of rabbits, &c. to the same cause. 



Dr. Morgan says : " Those ducks would have been most likely to 

 remain in confinement that had less well-developed wings ; and hence at 

 the start artificial selection may have served to bring about the result " 

 (p. 94). But analogous structures with correlated habits among long- 

 domesticated beings are innumerable, and never to be seen in wild 

 animals, as they would be quickly exterminated ; how then could they 

 have arisen except in consequence of disuse under domestication ? 



On the other hand, fowls which have escaped into woods and breed 



* By T. H. Morgan, Ph.D. 



f Origin of Species, 6th ed., pp. 6, 7, and Animals and Plants under Domestica- 

 tion, ii. 271. 



% " Variability," i.e. the capability of varying, is often used by writers, including 

 Darwin, for " variation," i.e. the result of variability. 



