404 



NATURE 



[Sept. 7, 1876 



production of the gorgeous train of the peacock and of the two 

 kinds of flower in the primrose ? The solution of these and a 

 hundred other problems of like nature, was rarely approached 

 by the old method of study, or if approached was only the 

 subject of vague speculation. It is to the illustrious author of 

 the " Origin of Species " that we are indebted, for teaching us 

 how to study nature as one great, compact, and beautilully 

 adjusted system. Under the touch of his magic wand the count- 

 less isolated facts of internal and external structure of living 

 things — their habits, their colours, their development, their 

 distribution, their geological history, — all fell into their approxi- 

 mate places ; and although from the intricacy of the subject and 

 our very imperfect knowledge of the facts themselves, much still re- 

 mains uncertain ; yet we can no longer doubt that even the minutest 

 and most superficial peculiarities of animals and plants either, 

 on the one hand, are or have been useful to them, or, on the 

 other hand, have been developed under the influence of general 

 laws, which we may one day understand to a much greater extent 

 than we do at present. So great is the alteration effected in our 

 comprehension of nature by the study of variation, inheritance, 

 cross-breeding, competition, distribution, protection, and selec- 

 tion — sliowing, as they often do, the meaning of the most obscure 

 phenomena, and the mutual dependence of the most widely- 

 separated organisms, that it can only be fitly compared with the 

 analogous alteration produced in our conception of the universe 

 by Newton's grand discovery of the law of gravitation . 



I know it will be said (and is said), that Darwin is too highly 

 rated ; that some of his theories are wholly and others partially 

 erroneous, and that he often builds a vast superstructure on a 

 very uncertain basis of doubtfully interpreted facts. Now, even 

 admitting this criticism to be well founded— and I myself believe 

 that to a limited extent it is so — I neveitheless maintain that 

 Darwin is not and cannot be too highly rated. For his greatness 

 does not at all depend upon his being infallible, but on his 

 having developed, with rare patience and judgment, a new system 

 of observation and study, guided by certain general principles 

 which are almost as simple as gravitation, and as wide-reaching 

 in their effects. And if other principles should hereafter be dis- 

 covered, or if it be proved that some of his subsidiary theories 

 are wholly or partially erroneous, this very discovery can -only 

 be made by following in Darwin's steps, by adopting the 

 method of research which he has taught us, and by largely using 

 the rich stores of material which he has collected. The " Origin 

 of Species," and the grand series of works which have succeeded 

 it, have revolutionised the study of biology. They have given 

 us new ideas and fertile principles. They have infused life and 

 vigour into our science, and have opened up hitherto unthought 

 of lines of research on which hundreds of eager students are now 

 labouring. Whatever modifications some of his theories may 

 require, Darwin must none the less be looked up to as the 

 founder of philosophical biology. 



As a small contribution to this great subject, I propose now 

 to call your attention to some curious relations of organisms to 

 their environment, which seem to me worthy of more systematic 

 study than has hitherto been given them. The points I shall 

 more especially deal with are — the influence of locality, or of 

 some unknown local causes, in determining the colours of insects 

 and, to a less extent, of birds ; and the way in which certain 

 peculiarities in the distribution of plants may have been brought 

 about by their dependence on insects. The latter part of my 

 address will deal with the present state of our knowledge as to 

 the antiquity and early history of mankind. 



On some Relations of Living Things to their Environment. 



Of all the external characters of animals, the most beautiful, 

 the most varied, and the most generally attractive, are the bril- 

 liant colours and strange yet o'ten elegant markings with which 

 so many of them are adorned. Yet, of ail characters, this is 

 the most difficult to bring under the laws of utility or of physical 

 connection. Mr. Darwin — as you are well aware — has shown 

 how wide is the influence of sex on the intensity of colouration ; 

 and he has been led to the conclusion that active or voluntary 

 sexual selection is one of the chief causes, if not the chief cause, 

 of all the variety and beauty of colour we see among the higher 

 animals. This is one of the points on which there is much diver- 

 gence of opinion even among the supporters of Mr. Darwin, and 

 one as to which I myself differ from him. I have argued, and 

 still believe, that the need of protection is a far more efficient 

 cause of variation of colour than is generally suspected ; but 

 there are evidently other causes at work, and one of these seems 

 to be an influence depending strictly on locality, whose nature 



we cannot yet understand, but whose effects are everywhere to be 

 seen when carefully searched for. 



Although the careful experiments of Sir John Lubbock have 

 shown that insects can distinguish colours — as might have been 

 inferred from the brilliant colours of the flowers which are such 

 an attraction to them — yet we can hardly believe that their appre- 

 ciation and love of distinctive colours is so refined as to guide 

 and regulate their most powerful instinct — that of reproduction. 

 We are therefore led to seek some other cause for the varied 

 colours that prevail among insects ; and as this variety is most con- 

 spicuous among butterflies, — a group perhaps better known than 

 any other — it offers the best means of studying the subject. The 

 variety of colour and marking among these insects is something 

 marvellous. There are probably about ten thousand different 

 kinds of butterflies now known, and about half of these are so 

 distinct in colour and marking that they can be readily distin- 

 guished by this means alone. Almost every conceivable tint and 

 pattern is represented, and the hues are often of such intense 

 brilliance and purity as can be equalled by neither birds nor 

 flowers. 



Any help to a comprehension of the causes which may have 

 concurred in bringing about so much diversity and beauty must 

 be of value, and this is my excuse for laying before you the more 

 important cases I have met with of a connection between colour 

 and locality. 



Our first example is from tropical Africa, where we find two 

 unrelated groups of butterflies belonging to two very distinct 

 families (Nymphalidte and Papilionida) characterised by a pre- 

 vailing blue green colour not found in any other continent.^ 

 Again, we have a group of African Pieridse which are white or 

 pale yellow with a marginal row of bead-like black spots, and in 

 the same country one of the Lycsenidse {Liptena erastus) is 

 coloured so exactly like these that it was at first described as a 

 species of Pieris. None of these four groups are known to be 

 in any way specially protected so that the resemblance cannot 

 be due to protective mimicry. 



In South America we have far more striking cases. For in 

 the three sub-families — Danainae, Acraaniae, and Heliconiinse — 

 all of which are specially protected, we find identical tints and 

 patterns reproduced, often in the greatest detail, each peculiar 

 type of coloration being characteristic of distinct geographical 

 subdivisions of the continent. Nine very distinct genera are im- 

 plicated in these parallel changes — Lycorea, Ceratinia, Mecha- 

 nitis, Ithomia, Melincra, Ttlhorea, Acrcea, Heliconius, and 

 Eueides — groups of three or four (or even of five) of them ap- 

 pearing together in the same livery in one district, while in an 

 adjoining district most or all of them undergo a simultaneous 

 change of coloration or of marking. Thus in the genera Ithomia, 

 Mechanitis, and Heliconius, we have species with yellow apical 

 spots in Guiana, all represented by allied species with white 

 apical spots in South Brazil. In Mechanitis, Melincea, and 

 Heliconius, and sometimes in Tithorea, the species of the 

 Southern Andes (Bolivia and Peru) are characterised by an 

 orange and black livery, while those of the Northern Andes 

 (New Grenada) are almost always orange-yellow and black. Other 

 changes of a like nature, which it would be tedious to enumerate, 

 but which are very striking when specimens are examined, 

 occur in species of the same groups inhabiting these same 

 localities, as well as Central America and the Antilles. The 

 resemblance thus produced between widely different insects is 

 sometimes general, but often so close and minute that only a 

 critical examination of structure can detect the difference between 

 them. Yet this can hardly be true mimicry, because all are alike 

 protected by the nauseous secretion which renders them unpalat- 

 able to birds. 



In another series of genera {Catagramma, Callithea, and 

 Agrias), all belonging to the Nymphalidre, we have the most 

 vivid blue ground, with broad bands of orange-crimson or a 

 different tint of blue or purple, exactly reproduced in correspond- 

 ing, yet unrelated species, occurring in the same locality ; yet, as 

 none of these groups are protected, this can hardly be true 

 mimicry. A few species of two other genera in the same country 

 (Eunica and Siderone) also reproduce the same colours, but with 

 only a general resemblance in the marking. Yet again, in 

 Tropical America we have species of Apatura which, sometimes 

 in both sexes, sometimes in the female only, exactly imitate the 

 peculiar markings of another genus [He'-erochroa) confined to 

 America. Here, again, neither genus is protected, and the 

 similarity must be due to unknown local causes. 



' Romaleosonta and Euryphene (Nymphalida:), Papilio zalmoxis, and 

 several species of the Nireus group (Papilionidse). 



