NATURE 



217 



THURSDAY, JANUARY 4, 1899- 



PHYSIOLOGY WL^^v?, NATURAL SELECTION: 



AN UNNATURAL ANTITHESIS. 

 Colour in Nature : a Study in Biclooy. By Marion 



I. Newbigin, D.Sc. (Lond.). Pp. xii + 344. (London : 



John Murray, 1898.) 



THE authoress states in the preface that her object is 

 "to set forth in systematic order the main facts at 

 present known in regard to the Pigments and Colours of 

 Plants and Animals," and especially to treat the physio- 

 logical side of the subject, and bring together the 

 scattered literature which deals with it. 



The first three chapters are introductory, dealing with 

 general questions of importance for the remainder of the 

 Mork — such as the differences between pigmental and 

 structural colours, and the classification of both these 

 <;itegories. Colours and pigments are then considered 

 throughout the plant and animal worlds, the subjects 

 treated in consecutive chapters being plants ; Protozoa 

 sponges and Coelentera ; worms ; Crustacea and Echino- 

 dcrmata ; Lepidoptera ; insects in general and spiders ; 

 Mollusca and invertebrates generally ; fish ; amphibians 

 and reptiles ; birds (occupying two chapters) ; mammals 

 and the origin of pigments. The concluding chapter 

 " on the relation of facts to theories " contains a general 

 >uminary and a brief exposition and criticism of various 

 theories as to the origin of colour. The list of references, 

 admitted to be incomplete, will nevertheless be useful, 

 although it is to be hoped that in a future edition 

 mention will be made of Colonel Swinhoe's complete 

 paper "On the Mimetic Forms," &c., in the Linnean 

 /ournai, instead of to the brief abstract in the Troc. 

 Roy. Sflc. 



The writer again and again protests against the 

 interpretation of colour phenomena by natural selection, 

 and implies that those who incline to accept this in- 

 terpretation are satisfied with casual suggestions which 

 tliey make no attempt to test. The present writer be- 

 lieves that the exact opposite is the truth, and that in 

 the whole history of biological thought no theoretical 

 suggestions have been so fruitful of extended and precise 

 observations as those based upon this very hypothesis. 



Whenever a writer ventures to suggest such an inter- 

 pretation, it is assumed by opponents that he is satisfied 

 to leave the matter at this point without the thought of 

 any further investigation by way of confirmation. This 

 is an assumption, and a most unfair assumption. Those 

 who have found natural selection a sure guide to research, 

 who cannot pursue all the varied lines which it indicates, 

 are glad to offer the same inspiration to other workers. 

 " A few magic words upon natural selection " (p. 24) are 

 not intended to " dismiss " any problem in natural history, 

 but rather to suggest lines of research by which it may 

 be attacked. 



It is interesting to note that this extremely critical 

 attitude as regards natural selection is not accompanied 

 by any special reticence in the use of other hypotheses. 

 Thus, as regards birds and butterflies, 

 NO. 1575, ^O^- ^I ] 



"ihe fact of the exquisite structural coloration and a 



wonderful development of structures arising from the 

 cuticle, suggests that the structural colours are merely 

 a result of extreme differentiation of the cuticle, and 

 therefore produced by the same cause which gave rise 

 to this differentiation" (p. 11). 



Again, on p. 155, the persistence of green pigments 

 derived from the larval food into the ova (and, in fact, 

 into the young which hatch from them) is quoted from 

 the present writer ; and the authoress then proceeds to 

 suggest that the green colour found by Mr. F. Gowland 

 Hopkins in the Pierinae is of the same kind. This 

 unsupported suggestion is very probably sound, and had 

 been independently arrived at by the present writer, who 

 is also inclined to extend it to the green pigments 

 doubtless derived from the blood (hiemolymph), which 

 are stored, as in the Pierinae., between the two wing 

 membranes, and give rise to the bright green or some- 

 times blue-green bands or spots in certain Nymphalinae 

 {Colaenis dido, Victorina steneles) and Papilioninae {P. 

 sarfiedon, &c.). Such a suggestion is reasonable, and 

 may well lead to specially directed research ; but a 

 similar spur to inquiry, if based on the theory of natural 

 selection, would have been held up to contempt by the 

 authoress. 



The freedom with which even flimsy and worthless 

 speculation is indulged in, if only an explanation founded 

 on natural selection can be thereby avoided, is well seen 

 on pages 161 and 162, where the warning colours of 

 Heliconidae and the mimetic or convergent Pierinae are 

 briefly discussed. The writer suggests that the slow 

 flight and warning colour of Heliconidae and their 

 mimics are due to "the relatively low organisation which 

 renders pigmentation by waste products possible, which 

 makes brilliant optical colours impossible." 



First, as to "low organisation," the Insecta are ad- 

 mittedly among the most specialised of animals ; except- 

 ing the Diptera there are no more specialised insects 

 than the Lepidoptera ; among Lepidoptera the It/iomiinae 

 (Bates' Danaoid Heliconidae, Trimen's Heliconoid 

 Danaidae) are the most specialised, and the Heliconinae 

 proper (Bates' Acraeoid Heliconidae) only less so. 



Secondly, as to " pigmentation by waste products," Mr. 

 Gowland Hopkins' observations prove that the pigments 

 of the Heliconidae are not the same as those of the 

 Pierines which resemble them. The latter alone have been 

 shown to possess wing pigments of uric acid or sub- 

 stances allied to it. 



Thirdly, as to brilliant optical colours being rendered 

 impossible. There are numerous examples of iridescence 

 in Jthotniinae, and some structural blues in the far less 

 numerous Heliconinae proper, while m the Danainae 

 which are closely related to the former the structural 

 blues of many much-mimicked Euploeina are mag- 

 nificently developed. 



The writer is apparently desirous of rejecting an inter- 

 pretation which explains an immense body of facts, and 

 has led to the discovery of an immense number more,, 

 in order to substitute a crude suggestion which, for its 

 mere statement, requires the distortion of many well 

 ascertained facts. 



It is only fair to add, however, that the writer recog- 



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