NATURE 



THURSDAY, DECEMBER 8, 1898. 



'I PHYSIOLOGICAL SELECTION, 



r^arzc'in, and after Darwin. By Dr. G. J. Romanes. 

 Pp. viii + 181. (London : Longmans, Green, and 

 Co., 1897.) 



rHIS third volume concludes the series "Darwin, 

 and after Darwin" of which G. J. Romanes had 

 ublished the first volume and had planned and mostly 

 ritten the remaining two, at the time of his death. 

 ,'his volume, as well as the second, has been prepared 

 ■)r the press under the able editorship of Prof. Lloyd 

 lorgan, who has performed a diflicult task with con- 

 picuous success. In a brief preface we are told that 

 le first two chapters and the last were in type at the 

 me of the author's death, and remain practically un- 

 hanged : while the editor is responsible for the selection 

 nd arrangement of the remaining three. The Appendices 

 'l and B, bearing upon the controversy with Alfred 

 tussel Wallace, " remain in accordance with the 

 mthor's expressed injunctions." The frontispiece to the 

 «lume is a portrait of the Rev. J.T. Gulick, whose most 

 ..iteresting researches into the variation of the land- 

 hells of the Sandwich Islands led him, independently, 

 pa theory closely similar to that of "physiological 

 election." 



I Of all the three volumes of this series, this possesses 

 jie greatest personal interest ; for it is devoted to the 

 Nxposition and discussion of the evidence for and against 

 he much debated hypothesis of physiological selec- 

 ion, which, although never widely accepted, always re- 

 hained dear to its creator. The present volume, which 

 :iossesses many advantages over the original account 

 'if the hypothesis published in the Linnean Society's 

 journal, will do much to enable biologists clearly to 

 'rasp the author's meaning. 

 The two first chapters deal with "isolation " in general, 

 principle which was given a position of the utmost 

 .Tiportance by the author, who regarded not only his 

 jlwn physiological selection, but natural selection itself 

 s a special form of isolation. The third, fourth and 

 ;fth chapters deal with "physiological selection " and its 

 'vidences ; the sixth again returns to " isolation " as a 

 [ictor in "organic evolution," and also contains the 

 (general conclusions." .Appendix A contains Mr. 

 '■ulick's criticism of Mr. Wallace's views on physio- 

 bgical selection ; 15, an examination by Mr. Fletcher 

 ^loulton of a calculation by Mr. Wallace on the same 

 ubject ; C, " some extracts from the author's note- 

 i)ook." 



j In the discussion of isolation the author first distin- 

 .juishes between indiscriiitinutc isolation such as would 

 j)e produced by some sudden geographical change separ- 

 iting the individuals of a species into two detachments, 

 [knd discriminate isolation such as would be caused by a 

 part of the species seeking some new area, or some dif- 

 I'erent habitat on the same area. While Mr. Gulick 

 Vecognised this distinction under the terms "separate 

 breeding" and "segregate breeding," the author suggests 



apogamy" and "homogamy." He says, moreover, 

 with the exception of Mr. Gulick, I cannot find that any 

 NO. 1519, VOL. 59] 



other writer has hitherto stated this supremely important 

 distinction between isolation as discriminate and indis- 

 criminate." But the classes of facts to which he alludes 

 are distinguished by every writer and thinker on evolu- 

 tion : the only difference being that the author is peculiar 

 in making isolation the basis of his classification. Other 

 writers have used the term " isolation " for the cases in 

 which separation is the primary and essential factor, 

 viz. for "indiscriminate isolation " only ; "discriminate 

 isolation" they have classified as "natural selection " or 

 as " Lamarckian evolution," as the case may be, the 

 separation being regarded as a secondary result. 



The whole discussion of isolation in the exalted posi- 

 tion in which it is placed by the author (" the whole 

 theory of organic evolution becomes neither more nor 

 less than ... a theory of the causes which lead to dis- 

 criminate isolation," p. 6) is interesting and suggestive, 

 and a large part of it convincing. It is also for the most 

 part clear and lucid in treatment, although sentences 

 occur which seem unnecessarily to demand the strained 

 attention of the reader. Thus after arguing that diversi- 

 fication of character is promoted but never originated by 

 natural selection, the author concludes, in the following 

 complicated passage : 



"Therefore the change must in all cases have been 

 due, in the first instance, to some other form of isolation 

 than the superadded form which afterwards arose from 

 superior fitness in the possession of superior benefit — 

 although, so long as the prior form of isolation endured, 

 or continued to furnish the necessary condition to the 

 co-operation of the survival of the fittest, survival of the 

 fittest would have continued to increase the divergence 

 of character in as many ramifying lines as there were 

 thus given to its action separate cases of isolation by 

 other means " (p. 32). 



The ideas sought to be conveyed in this quotation are 

 not difficult of comprehension, but the form is such that 

 they become intelligible only with effort. 



Physiological selection is defined by the author at the 

 opening of the third chapter as "that form of isolation 

 which arises in consequence of mutual infertility between 

 the members of any group of organisms and those of 

 all other similarly isolated groups occupying simul- 

 taneously the same area." The two great difficulties in 

 the way of natural selection as a sufficient explanation 

 of the origin of species are held to be the difference 

 between domesticated varietfes and natural species in 

 respect to cross fertility, and "the fact that natural 

 selection cannot possibly give rise to polytypic as dis- 

 tinguished from monotypic evolution." The former diffi- 

 culty has long been felt, and it was the great logical flaw 

 which always prevented Huxley from declaring his 

 entire conviction in the soundness of the theory. The 

 author is certainly right in claiming for physiological 

 selection that it would tend towards the removal of this 

 difficulty. As to the second difficulty the majority of 

 Darwinians will not be convinced by the author's reasons 

 for thus limiting the power and scope of natural selection. 



The conception of physiological selection — the idea 

 that the differentiation of species begins with infertility 

 instead of ending with it — is here shown to ha\ e arisen 

 independently in many minds, having been first mentioned 

 by Belt (1874), then by Catchpool (1884), Romanes 

 (1886), and Gulick (1887). 



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