To J. D. Hooker   16 [May 1857]

Down Bromley Kent

16th

My dear Hooker

You said, I hope honestly, that you did not dislike my asking questions on general points,—you of course answering, or not, as time & inclination might serve.

I find in animal kingdom that the proposition that any part or organ developed (normally (ie not monstrosity)) in a species in any high or unusual degree, compared with the same part or organ in allied species, tends to be highly variable.1 I cannot doubt this, from my mass of collected facts.— To give instance, the Cross-Bill is very abnormal in structure of Bill compared with other allied Fringillidæ, & the Beak is eminently variable.—2 The Himantopus remarkable from wonderful length of legs, is very variable in length in length of legs.—3 I cd. give many most striking & curious illustrations in all classes;—; so many that I think it cannot be chance. But I have none in vegetable kingdom, owing, as I believe, to my ignorance.— If Nepenthes consisted of one or two species in group with pitcher developed, then I shd. have expected it to have been very variable; but I do not consider Nepenthes case in point, for when a whole genus or group has an organ, however anomalous, I do not expect it to be variable,—it is only when one or few species differ greatly in some one part or organ from the forms closely allied to it in all other respects, that I believe such part or organ to be highly variable.—4 Will you turn this in your mind: it is important apparent law (!) for me.—5

Ever your’s | C. Darwin

P.S. I do not know how far you will care to hear, but I find Moquin-Tandon treats in his Teratologie on villosity of plants & seems to attribute more to dryness than altitude;6 but seems to think that it must be admitted that mountain plants are villose, & that this villosity is only in part explained by De Candolles remark, that the dwarfed condition of mountain plants, would condense the hairs, & so give them the appearance of being more hairy. He quotes Senebier Phys. Veg. as authority, I suppose first authority, for mountain plants being hairy.—7

If I could show positively that the endemic species were more hairy in dry district, then the case of the vars. becoming more hairy in dry ground, would be fact for me.—

1
CD had previously asked Hooker, Hewett Cottrell Watson, and Asa Gray about this particular phenomenon (Correspondence vol. 5). CD was at this time working on his chapter on the ‘Laws of variation’ (Natural selection, pp. 279–338), which was completed on 5 July 1857 (‘Journal’; Appendix II).
2
In his discussion of this apparent rule in Natural selection, pp. 307–18, CD mentioned the case of the crossbill and cited Macgillivray 1837–52, 1: 423, on the great variability ‘in length, curvature & the degree of elongation of lower mandible’ (Natural selection, p. 310).
3
‘The long-legged Plover or Himantopus forms a small genus with closely allied species, quite remarkable from their extraordinary length of the legs compared with their nearest allies.’ (Natural selection, p. 310).
4
Hooker had offered Nepenthes as a case in point in response to CD’s earlier query (see Correspondence vol. 5, letter to J. D. Hooker, [April 1852], n. 10).
6
Moquin-Tandon 1841, pp. 65–7. See also Natural selection, p. 283.
7
Horace Bénédict Alfred Moquin-Tandon cited Senebier [1800] in his discussion of this point (Moquin-Tandon 1841, p. 66 n. 2).

Manuscript Alterations and Comments

2.2 (ie not monstrosity)] interl
2.3 or organ] interl
2.5 is very] ‘is’ interl
2.7 is very] ‘is’ interl
2.7 in length of legs] interl
2.8 in all classes;—] interl
2.10 or two] interl
2.10 group] above del ‘genus’
2.11 have expected] ‘have’ interl
2.11 to have] ‘have’ interl
2.11 been] altered from ‘be’
2.11 very] interl
2.11 but I do … point, for] added after del ‘for’
2.14 part or organ] above del ‘respect’
2.14 the] interl
2.14 to it] interl
2.15 such part or organ] ‘or organ’ interl
2.16 your] interl
4.4 part] altered from ‘parts’
4.5 condense the] ‘the’ altered from ‘them’
4.5 hairs] interl
5.1 positively] interl

Please cite as “DCP-LETT-2092,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-2092