i68 SCIENCE PROGRESS 



small individual variations on which the theory of natural selection chiefly depends 

 are of little importance in evolution. There is no objection to controversy per se. 

 So long as investigators form different conclusions on the same subject, controversy 

 is unavoidable. It is not merely necessary, but advantageous ; even if opponents 

 do not convince each other they help others to more correct judgment. Darwin 

 himself did not abstain from controversy— he considered and replied to the objections 

 brought against his theory. It is the introduction of the personal note in contro- 

 versy which is to be deprecated ; and when Prof. Poulton compares de Vries, 

 Bateson, and Punnett to builders of Babel who do not understand one another's 

 speech, one cannot help feeling that he is exceeding the legitimate bounds of 

 scientific argument. 



The point at issue is the heredity of individual variations, or more precisely the 

 opinion of de Vries concerning their heredity. De Vries termed such variations, 

 which universally occur among the individuals of the same species and even of the 

 same parentage, fluctuations. According to Mr. Shipley's address to the Zoo- 

 logical Section of the British Association at Winnipeg in 1909, fluctuations are due 

 to external conditions, and are probably not inherited. Mr. Shipley's statement 

 was adopted from Mr. Punnett's little book Mendelisin. Prof. Bateson writes that 

 de Vries for the first time pointed out the distinction between the impermanent 

 and non-transmissible variations which he calls fluctuations, and the permanent 

 and transmissible variations which he calls mutations. Prof. Poulton quotes 

 passages from de Vries, and from Hubrecht's expositions of the views of de Vries, 

 which prove, not that de Vries stated fluctuations to be hereditary, but that he 

 believed they could not, however much selected, lead to progressive evolution, 

 because as soon as the selection ceased the organism would return to its original 

 condition. In Prof. Poulton's opinion this view necessarily implies a belief in the 

 hereditary transmission of fluctuations. But when Bateson refers to fluctuations 

 as impermanent and non-transmissible he does not appear to mean anything more 

 than de Vries meant by saying that continued selection has no appreciable effect 

 on them, or than Galton meant by regression towards mediocrity ; and Prof. 

 Poulton accepts Gal ton's principle as true. Both Galton and de Vries agree that 

 when an individual fluctuation is selected for breeding, the offspring present 

 variations round the degree of greatest frequency, which may not be the same 

 as the parental character. According to the mutationists, when a mutation occurs 

 the offspring all present the particular character which constitutes the mutation. 

 This is all that Bateson means by saying that a mutation is transmissible, a 

 fluctuation not. 



The most important paper in Prof. Poulton's volume as a contribution to science 

 is that on Mimicry in the Butterflies of North America. In such a subject the 

 author is thoroughly at home, and has an unrivalled knowledge of the facts — facts 

 in themselves of the greatest interest ; but whether they support the conclusions 

 the author draws from them is another question. Even after fifty years of 

 Darwinism the main assumptions on which the MuUerian hypothesis of mimicry 

 rests are as far from definite proof as ever. There is no conclusive evidence that 

 the steps by which one distasteful species came to resemble another were small 

 indefinite variations, though Prof. Poulton considers that a comparison of the 

 mimetic Lhnenitis archippus and the non-mimetic L. arthemis supplies such 

 •evidence. In the next place it is difficult to understand how " the advantage of 

 a common advertisement " could be sufficient to bring about the amount of selection 

 required to produce the actual similarity of coloration between two species both 

 inedible. According to Prof. Poulton's explanation the mimetic L. archippus has 



