Some Evidence against the Theory off the Origin 



off Species by Natural Selection off Infinitesimal 



Variations, and in ffavour off Origin 



by Mutation. i-ibi^akv 



bota' 



J. C. WILLIS. (j.,. . ^ 



TT may seem somewhat superfluous to bring up at this 

 -*- period evidence against the theory of natural selection of 

 infinitesimal variations, but as the opposition theory of origin 

 of species by mutation is by no means generally accepted, it 

 may be well to produce a fairly trenchant argument which was 

 suggested to me by my work upon the Flora of Ritigala.* It 

 must be made clear at the start that the evidence is not so 

 absolutely in favour of mutation as it is against selection of 

 infinitesimal variations, but at present the mutation theory 

 is the only one in the field which can be invoked to explain 

 the facts. t 



* Willis, Flora of Ritigala, an isolated Mountain. Ann. Perad. 

 III., 1906, p. 271. 



f For the benefit of Ceylon readers, who can hardly be expected to 

 be up to date in a matter of this kind, the following notes will make the 

 object of this paper a little more clear. No one at this period of time 

 can doubt that an evolution of species has gone on, and it is Darwin's 

 great service to have proved this. But there is now much dispute 

 going on as to the way in which this evolution took place. The current 

 theory, and that accepted by most of the disciples of Darwin — though 

 he himself never, so far as can be made out, adhered unreservedly to 

 it — is that the changes necessary to give rise to a new species take place 

 by the natural selection of infmitesimal variations. To take a simple 

 illustration, the fruits of a certain plant were measured, and it was found 

 that 568 of them showed lengths represented below, the lengths being 

 given in the upper column, the number of fruits showing them in the 

 lower : — 



15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 

 '^ 1 1 5 11 17 27 37 62 74 83 79 51 43 32 18 13 5 5 3 1 



CD [Annals of the Royal Botanic Gardens, Peradeniya, Vol. IV., Part I., May, 1907.] 



7(3)07 (J) 



?ND 



•^ 



