To H. W. Bates 26 March 
Down Bromley Kent
I have read your papers with extreme interest & I have carefully read every word of them.1 They seem to me to be far richer in facts on variation, & especially on the distribution of varieties & subspecies, than anything which I have read. Hereafter I shall reread them, & hope in my future work to profit by them & make use of them. The amount of variation has much surprised me. The analogous variation of distinct species in the same regions strikes me as particularly curious. The greater variability of female sex is new to me. Your Guiana case seems in some degree analogous, as far as plants are concerned, with the modern plains of La Plata, which seem to have been colonised from the north, but the species have been hardly modified.—
I have been particularly struck with your remarks on the Glacial period.2 You seem to me to have put the case with admirable clearness & with crushing force. I am quite staggered with the blow & do not know what to think. Of late several facts have turned up leading me to believe more firmly that the Glacial period did affect the Equatorial Regions; but I can make no answer to your argument; & am completely in a cleft stick. By an odd chance I had only a few days ago been discussing this subject, in relation to plants, with Dr. Hooker, who believes to a certain extent; but strongly urged the little apparent extinctions in the Equatorial regions. I stated in a letter some days ago to him, that the Tropics of S. America seem to have suffered less than the Old World.3
There are many perplexing points, temperate plants seem to have migrated far more than animals— Possibly species may have been formed more rapidly within Tropics than one would have expected. I freely confess that you have confounded me: but I cannot yet give up my belief that the Glacial period did to certain extent affect the Tropics.—4
Would you kindly answer me 2 or 3 questions if in your power.— When species (A) becomes modified in another region into a well marked form (C), but is connected with it by one (or more) gradational form (B,) inhabiting an intermediate region; does this form (B) generally exist in equal numbers with (A) & (C), or inhabit an equally large area?— The probability is that you cannot answer this question: though one of your cases seem to bear on it.—
Has Mr Baly published on Chrysomelidæ: if so, or when he does, would you give me reference to his paper?5
In Butterflies, in which the sexes are differently coloured, is the male or female most beautiful in our eyes? Do you know in Tropics any strictly nocturnal moths with gaudy colours? As with Birds, have you ever noticed that female butterflies make any selection of the male with which they copulate? Do several males pursue same female? Are butterflies attracted by gay colours, as it has been asserted Dragon-flies are. Any authentic facts on the courtship of Butterflies would be most thankfully received & quoted by me. But I can see how very improbable it is that anything shd. have been observed.—6
You will, I think, be glad to hear that I now often hear of naturalists accepting my views more or less fully: but some are curiously cautious in running risk of any small odium in expressing their belief.
With cordial thanks & respect | Believe me my dear Sir | Yours sincerely | C. Darwin
(Have you received copy of new Edit. of Origin?)7
March 23d. 1861. Suppose world shortly before Glacial to have had present temperature; but we know before that it was hotter. Probably *the effect of this [interl] then would have been an [‘N. Tropical’ del] Equatorial Flora, which could live only in hottest regions; & a N. [interl] Tropical & S. Tropical Flora. [illeg del] fitted for less intense Heat, & distinct from each other, for they must have been separated from each other for long time by Equatorial Flora. During Glacial period, I suppose Equatorial Flora almost wholly annihilated. And the N. & S. Tropical Flora, which would not have suffered quite so much under Equator during Glacial period, to have occupied Equatorial regions. Their commingling would have made a rich Flora., & [over ‘—’] which now has become accustomed to rather hotter climate than that to which they were accustomed, [‘during’ del] previously to Glacial period.—
35o North N. Tropical Flora 25o N. Equator Equatorial Flora nearly all exterminated during Glacial period.— 20o S. S. Tropical Flora distinct from North. 35o S.All this upset by Mr Bates paper.— Can species have been very largely developed since glacial period.— Certainly from Lat 25o to Equator productions now ought to have very uniform character. How is this? | In [‘Brazil’ del] S. America immigration must have been almost exclusively by lines of mountains.—
Crowning difficulty is why equatorial productions not all destroyed—as climate [above del ‘some of temperate’] would have been best fitted for sub-tropical productions— Probably was & our present Tropical productions were [‘the’ del] sub-tropical before glacial— All Fauna & Flora much disturbed & a few temperate forms crossed owing to disturbance—taking advantage of high land—
With respect to S. America we have but little evidence of the 〈probability〉 of 〈such forms〉— Yet some seem to have crossed [del illeg] Region of Amazona [‘seems’ del] is greatest difficulty— Undoubtedly there is much to explain as yet
Comments on the great extent of variations and on the acknowledgment of the new idea of greater female variety.
Expresses belief that the glacial period did affect the tropics, though HWB’s arguments have confounded him.
Poses a series of questions concerning sexual selection.
- Letter no.
- Darwin, C. R.
- Bates, H. W.
- Sent from
- Source of text
- Cleveland Health Sciences Library (Robert M. Stecher collection)
- Physical description
Please cite as
Darwin Correspondence Project, “Letter no. 3100,” accessed on 24 January 2017, http://www.darwinproject.ac.uk/DCP-LETT-3100