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Darwin Correspondence Project

To Thomas Davidson   23 December [1856]1

Down Bromley Kent

Dec. 23d

Dear Sir

I do not know whether you will forgive me, a stranger to you personally though not to your works, taking the liberty of begging a favour of you.—2 Namely to ask for a piece of information, which you are more likely to be able to give than anyone, though it is doubtful whether you will be able.— I am particularly anxious to know & be permitted to quote (if I find it desirable) any fact showing, that a variable species is or is not equally variable at all times & places.—3 Some facts seem to show that a species may vary far more in one area than in another; & some other, & perhaps more numerous, facts seem to indicate that a variable species is always equally variable.

With your profound knowledge of Brachiopoda, you may be able to give me examples & inform me how this is, with the species which have had a long existence or wide range.— Of course in order to judge, specimens must have been examined nearly equal in number at the two times or places.— Variability in close connexion with or caused by attachment to various substances would probably be alike at all times; so that there are many difficulties in coming to any conclusion.4

I formerly talked on this subject with the late E. Forbes, & more recently with Mr Woodward of the British Museum, but could get no definite light.—5 If you are willing to give me information on this head, I shd. esteem it a great kindness, which I have no right to expect, except as a fellow student in Natural History.

I beg to remain | Dear Sir | Yours faithfully | Ch. Darwin


Dated by the relationship to the letter from Thomas Davidson, 29 December 1856.
Davidson was a fellow of the Geological Society of London and the author of works on Brachiopoda, particularly a monograph on fossil brachiopods (Davidson 1851–86).
CD had begun writing chapter 4 of his species book, ‘Variation under nature’ (Natural selection, pp. 95–171). In his discussion of individual variations, CD stated that: ‘I have applied, also to Mr. Davidson, whose vast experience in Brachiopodous shells, makes his opinion of the highest value’ (Natural selection, p. 106).
In Natural selection, p. 106, CD reported that: ‘innumerable examples could be given of the foregoing cases [of variability] & this was all that I could learn on this subject from the late Prof. E. Forbes & from Mr. Woodward.’ See letters from S. P. Woodward, 2 May 1856 and 15 July 1856.


Davidson, Thomas. 1851–86. British fossil Brachiopoda. 6 vols. London: Palæontographical Society.

Natural selection: Charles Darwin’s Natural selection: being the second part of his big species book written from 1856 to 1858. Edited by R. C. Stauffer. Cambridge: Cambridge University Press. 1975.


Asks TWStCD about variation among brachiopods.

Letter details

Letter no.
Charles Robert Darwin
Thomas Davidson
Sent from
Source of text
American Philosophical Society (Mss.B.D25.142)
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 2021,” accessed on 17 September 2021,

Also published in The Correspondence of Charles Darwin, vol. 6