NATURE 



313 



THURSDAY, AUGUST 4, 1904. 



'• .Urr.lT/OA-" V. SELECTION. 

 Evolution and Adaptation. By Thomas Hunt Morgan, 

 Ph.D. Pp. xiii + 470. (New York : The Macmillan 

 Company; London : Macmillan and Co., Ltd., 1903.) 

 Price 12.S. 6d. net. 



THE author of the present work is one of those 

 biological theorists who, while accepting the 

 doctrine of evolution, and apparently admitting that 

 natural jihenomena must be capable of rational ex- 

 planation, vet think it necessary to adopt a severely 

 iritical attitude towards the only principle which seems 

 ;il)lc to account for the facts of organic development, 

 the principle, namelv, of selection, as first propounded 

 and illustrated by Darwin and Wallace. 



.Among the difficulties which those who impugn the 

 doctrine of selection have to face, the existence of 

 adaptation in every department of organic nature is 

 one of the most formidable. After every allowance 

 has been made for hasty allegations which further 

 knowledge has tended to disprove, there remains an 

 immense body of facts relating to the adjustment of 

 organisms to their surroundings that demands to be 

 accounted for in accordance with the known laws of 

 nature. What rational means of explanation are still 

 open to those who would dispense with the Darwinian 

 key to the puzzle of adaptation ? This is, in brief, the 

 question which Dr. Morgan asks and attempts to 

 answer in the volume before us. It is true that his 

 acceptance of the facts of special adjustment is some- 

 what grudging; even in the case of Kallima, which, 

 as Weismann says, is "decisive for adaptation," he 

 .appears to question the utility of the very perfect con- 

 cealment afforded by the underside. But whatever 

 scepticism he may be justified in showing with regard 

 lo particular instances, neither he nor anyone else can 

 deny with reason the general principle of adaptation. 

 It must be set down to the author's credit that he does 

 not seek refuge in the views of the Lamarckian 

 school, whether new or old : — 



" Despite the large number of cases that they (the 

 Lamarckians) have collected, which appear to them 

 10 be most easily explained on the assumption of the 

 inheritance of acquired characters, the proof that such 

 inheritance i> possible," he justly says, " is not forth- 

 coming. " 



Where, then, are we to find a solution of the 

 mvbtery? The answer, according to Dr. Morgan, lies 

 in the " mutation theory " of De Vries. But here 

 comes in a curious inconsistency of which the author 

 himself seems to be partly, but only partly, aware. 

 If he urges one point with greater insistence than 

 another, it is that De Wies's theory " stands in sharp 

 contrast to the selection theory." Yet the whole drift 

 of his argument goes to show, though he seldom 

 acknowledges it in so many words, that even if 

 De Vries's account of " variations " and " mutations," 

 .ind of the relation between them be accepted, selec- 

 NO. I 8 14, VOL. 70] 



tion must still be called in to explain the aspect of the 

 world around us. 



Let us for the moment lav aside the subject of 

 the nature of variation, admitting that it is capable 

 of a more minute analysis than Darwin gave it, and 

 that much remains to be learned concerning different 

 kinds of variation and their power of transmission 

 by heredity. We are still face to face with the ques- 

 tion, " How is it that the favourable variations form 

 the majority of those that we see? What has become 

 of the others?" The answer shall be given in Dr. 

 Morgan's own words : — 



" Over and beyond," he says, " the primary question 

 of the origin of the adaptive, or non-adaptive, structure 

 is the fact that we find that the great majority of 

 animals and plants show distinct evidence of being 

 suited or adapted to live in a special environment, i.e. 

 their structure and their responses are such that they 

 can live and leave descendants behind them. I can 

 see but two ways in which to account for this con- 

 dition, either (i) teleologically, by assuming that only 

 adaptive variations arise, or (2) by the survival of only 

 those mutations that are sufficiently adapted to get a 

 foothold. Against the former view is to be urged that 

 the evidence shows quite clearly that variations 

 (mutations) arise that are not adaptive. On the latter 

 view the dual nature of the problem that we have to 

 deal with becomes evident, for we assume that, while 

 the origin of the adaptive structures must be due to 

 purely physical principles in the widest sense, yet 

 whether an organism that arises in this way shall 

 persist depends on whether it can find a suitable 

 environment." 



What is this but selection ? The fineness of the dis- 

 tinction here drawn appears to have struck the author 

 himself, for he immediately adds : — 



" This latter is in one sense selection, although the 

 word has come to have a different significance, and, 

 therefore, I prefer to use the term survival of species." 



We need not dispute over the term, provided that 

 the principle, which is essentially Darwin's, be 

 admitted. 



The more we examine Dr. Morgan's argument as 

 against Darwin, the greater dilificulty do we experi- 

 ence in defining the precise point at issue between 

 them. It is not the origin of variation ; for if Darwin 

 did not attempt to account for this, neither does 

 De Vries. Nor is it the existence of the discontinuous 

 variations called " mutations " by De Vries, for some 

 of these were well known to Darwin. Nor, again, is 

 it the principle of selection; for this, as we have seen, 

 is virtually admitted on all hands. We might have 

 been inclined to say that it was the question of the 

 origin of species by large as against small variations, 

 but for the fact that the author expressly states that 

 " as De Vries has pointed out, each mutation may 

 be different from the parent form in only a slight 

 degree for each point." We are reluctantly impelled 

 to the conclusion that the controversy is rather of a 

 personal than of a material nature, and that at the 

 root of it lies a kind of jealousy — no doubt unconscious 

 — of Darwin's position and influence. It would 



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