Darwin Correspondence Project

King St Leicester

28 March 1861

My Dear Sir

I received your kind letter today & think it better to reply at once, as I am going to London on Monday for a few days study at the Insect room Brit. Mus. & shall not have another opportunity very soon. It gives me very great pleasure to find that my paper is likely to be useful to you. I am quite convinced that Insects offer better or clearer illustrations of the problems you occupy yourself with than any other class of animals or plants. It is so easy with them to obtain great series of examples & have them before you in a small compass, which is one advantage they have.—

I do not think the result I have come to regarding the persistence of the Guiano-Amazonian fauna can be shaken. I can see no traces of a migration of high-temperate-zone forms across the region. Now there are a number of genera of insects characteristic of the high-temperate zones, which are now common to S. America & N. America with Europe; but they have not a single representative in Amazonia, although some of them have representatives along the Andes of New Granada & Peru. Your hypothesis only requires (as you have stated) a migration along belts of latitude & therefore I do not think that the conclusion I have come to affects your position much after all.— I am further confirmed in my view that no migration took place across Guiano-Amazonia by the fact that there is a migration going forward now, or has been within the historic period of species of a migratory genus of Butterflies, but although one or other of the forms has obtained a footing in most other regions of the world there is no trace of them in that country. I allude to the species of the genus Pyrameis of which there are two English species P. atalanta & P. cardui. The geographical distribution of the species of this genus is very peculiar & has often excited attention. The following is a sketch of the facts

P. atalanta is found throughout Europe & N. America as far South as Mexico. On the Southern slopes of the Himalaya, & in Madeira (!) it exists as P. Callirhoe considered by some as a local var. In Java it presents us with a further var. in P. Dejeanii: & in the Sandwich Islands another allied form, P. Tammeamea; It appears to go no further South than Java, & is not found in S. America. Pyrameis cardui is found throughout Europe, Africa to the cape of Good hope; Asia & the Asiatic islands to Australia & New Zealand, without varying.— In America it is found throughout the united states, in Venezuela it exists only as a var. P. Leachiana, throughout N. America it is found in conjunction with P. Huntera a very closely allied species; but the two have different areas, although existing together in some parts; To the west of the Andes from California to chili there exists another form of Cardui, viz P. Carye; and in the S. of Brazil another, P. Myrinna; in the Amazonian region not a trace of any of these forms is to be found. From these facts it would appear 1st. that Northern temperate forms more readily cross the equator in the old world than in the new; 2nd that they are subjected to far greater modifying or transforming influences in the New World than in the old, 3rd that the only passage made use of by them in the New world is the chain of the Andes. I should add that the species of Pyrameis are strongly migratory; many accounts at least of immense migrations of P. cardui having been published.—

When I read your book first, the chapter on Geogr. distr. of course struck me very much; but a doubt occurred to me whether the resemblance in the faunas & floras between the N. & S. temperate zones was of such a nature as to require the explanation you have given. I am quite ignorant of the nature of the curious resemblance in the plants of Tierra del fuego & am quite inclined to think my doubt is unfounded in this respect.

However, two considerations have presented themselves to me. 1st. there are in several classes of animals & plants groups which seem to have originated at a remote epoch of the worlds history, & which, in consequence of the limited nature of their variability have gone on repeating nearly similar specific forms in all countries where they exist up to the present time. In plants I am not aware it is any other class than the inferior Cryptogamia which are in this position; but in insects there are several groups. Two occur to me at the present time   the Hesperiadæ in the Lepidoptera & the Libellulidæ (Dragonflies) in the Neuroptera. Similar species of these are found all over the world. I will not dwell too long on the subject or my letter will run to great length. I wish to suggest whether it is possible that the Tierra del fuego plants belong to such a group as I have described. I know that they are not found (as you have stated) in the tropical zones, but are the genera found there; & are they of such a homomorphic nature (to coin a word) as I have described.—

The other consideration is that there are genera peculiar to the high temperate zones of both hemispheres which present in South America compact groups of species so very dissimilar to those of North America that it is out of the question that they could have been derived thence so lately as the glacial period. I will give you a strong & very intelligible case viz that of the Chilian species of Carabus, of which yourself discovered several of extreme beauty. The genus Carabus at the present time is not found in the Northern hemisphere, further south than 28o nor in the Southern further North than 33o.— The Chilian species number 11 & form a group distinguished by peculiarities of form & sculpture;— Now there is not a species that at all approximates those of N. America; there is an utter dissimilarity between the two groups. The nearest approach to the Chilian forms is presented in species of the South of Europe (perhaps some may occur in E. Asia). How did the Chilian Carabi get there, & why are they so different from those of the rest of the world?— To me this is a most interesting fact; it seems to point to a far more ancient Glacial epoch, than the post-tertiary one. The Carabi may be studied by any one in five minutes by consulting the ``Bowringian collection'' in the British Museum, where they are lucidly arranged.

With regard to the question you ask me—whether an intermediate local form B is numerous & widely dispersed between the ranges of its extreme forms A & C: the facts that I have on the subject are numerous & rather ill digested at present. They are complicated in themselves & difficult. I know many instances of two local forms separated by a wide space without apparent natural barriers, untenanted by intermediate forms. There are many others (closely allied) which exist together on their mutual frontiers without blending. There are others which are very polymorphic in a central region, whilst in other localities E. W. N. & S. segregated into several well defined local varieties or admitted species. I will mention now one case only that meets your question. It is one, whose correctness I am quite sure of. On the dry soils, supporting for the most part a thinner forest growth, of the hilly regions of Guiana & Venezuela there exists a conspicuous Heliconia, H. Melpomene, it is abundant also in the central parts of the lower Amazons where the Hilly sandy country occurs & is found on the N. & S. Shores in extreme profusion. In the moist alluvial plains eastward to Par´a & westward to Peru & Bolivia, not a single individual is to be seen. In its place, occupying exactly the same sphere as it were, is H. Thelxiope a form so strikingly peculiar in colours that no one has ever doubted it to be a perfectly distinct species; it swarms in individuals & is nearly constant in its specific characters. Now wherever this form comes into contact with Melpomene there exists a number of intermediate varieties many of which have been described as species: they are rare, & very restricted in range. They have puzzled Lepidopterists & it has been almost settled that they were hybrids. I am convinced they are not hybrids; I never saw Melpomene & Thelxiope in copula; and besides these pretended hybrids exist at Demerara & Cayenne, where Thelxiope does not occur. I am thoroughly convinced that Thelxiope is a local variety of Melpomene, having all the appearance of a species, but created by the influences to which it has been subjected, out of Melpomene; & that the intermediate forms are the gradations. I have found Melpomene in copula with these forms & perhaps it may sometimes be so with Thelxiope, but that would not affect the case much I think.

The group from which I have supplied this example is very interesting,—being restricted to S. America, which swarms with its species; & apparently a modern creation. I am now studying it with a view to writing upon it & I think I have got a glimpse into the laboratory where Nature manufactures her new species.

—The other question you ask me relates to sexual selection.— I have seen Papilios attracted by bright colours in the forest, namely by the scarlet sepals of certain plants having inconspicuous or no flowers. I have also seen repeatedly many males following a female.— On this subject I will point out to you the following facts. In the æneas section of the genus Papilio, the males are generally of extremely brilliant colours, velvety black vivid green, carmine, & red with opalescent reflections,—the females are plainer & so different from the males that they were generally held to be distinct species until I took them in copulˆa. Now it is not all the species that present this disparity. In one P. Panthonus the two sexes are exactly alike in colours, the male only being a trifle brighter; from this species the divergence may be traced getting wider & wider from species to species up to P. Sesostris or P. Childrenæ, where the dissimilarity reaches its highest point. There is exactly the same phenomenon presented in the genus Epicalia & others. The females, however, vary in localities;—& although I thoroughly believe in your theory of sexual selection yet I think that local circumstances have some effect on colours. I do not however think that sunlight is the direct cause of vivid colours, although beautifully coloured male butterflies are almost always in the sun (genus Catagramma) whilst their drab partners are in the shade. I think the causes lie in the abundance of food, warmth & moisture of the atmosphere & even in the sluggish state of the atmosphere because the brightest coloured butterflies are not generally found within the influence of the Atlantic sea breezes, but in the sultry valleys of the Andes & the centre of the continent & these causes operate on the larva & so by correlation on the perfect insect.

I cannot say that I have noticed female butterflies pointedly selecting their male partners. The extremely rich male butterflies of the genus Catagramma live & sport together in the sun light all day, whilst their plainer coloured females are confined to the shades of the forest. The males too appear to be very much more numerous than the females,— I think there is no doubt now about this significant fact   there must be many hundred males to one female of these butterflies, & in another genus Cybdelis where the males are also distinguished by rich colours the males are immensely more numerous than the females. In another beautiful genus, Megistanis no female has yet been found although the males are very numerous. In Callithea, however where the males are the most richly coloured of all butterflies, both sexes are found in equal numbers, but here the females are not much behind the males in beauty. The males which sport together all day in the sunlight disappear about 4--5 P.M. & I have watched them then flying off to the forest (towards the summits of the trees) where doubtless some of them find their mates.—

There are no strictly nocturnal Lepidoptera gaily coloured in the tropics: There is no scarcity of brilliantly cold. moths but they are all day fliers.

Perhaps the above facts will illustrate a little the problems of sexual disparity & beauty of colours. There is no phase of your theory I like better than its explanation of the subtle adaptations of organic beings. There is one topic which Entomology will help to illustrate viz. that of mimetic analogies. I have an immense number of facts on this subject. Some of these resemblances are perfectly staggering,—to me they are a source of constant wonder & thrilling delight. It seems to me as though I obtain a glimpse of an intelligent motive pervading nature, as well as of the mighty never-resting wonder working laws that regulate all things.—

—I received the copy of 3d edit. of the ``Origin'' a most valued present for which accept my thanks.— I received a letter from my friend Wallace last week   he was going to Timor

Believe me My Dear Sir Yours sincerely | H W Bates

There is a stupid error in my paper, the note referring to ``Recent & ancient fossil shells''. The secretary took upon himself to correct the proof, I saw it and forgot to erase it—