Ɛpsilon

To Charles Lyell   4 October [1867]1

Down. | Bromley. | Kent. S.E.

Oct 4

My dear Lyell

With respect to the points in yr note I may sometimes have expressed myself with ambiguity.2 At the end of Chap. 23 where I say “that marked races are not (often (you omit ”often“)) produced by changed conditions”, I intended to refer to the direct action of such conditions in causing variation, & not as leading to the preservation or destruction of certain forms.3 There is as wide a difference in these two respects, as between voluntary selection by man & the causes which induce variability. I have somewhere in my book referred to the close connection between Nat. Selection & the action of external conditions in the sense which you specify in your note. And in this sense all Natural selection may be said to depend on changed conditions.4

In the “Origin” I think I have underrated (& from the cause which you mention) the effects of the direct action of external conditions in producing varieties; but I hope in Chap. 23 I have struck as fair a balance as our knowledge permits.5

It is wonderful to me that you have patience to read my slips & I cannot but regret it, as they are so imperfect, they must I think give you a wrong impression; & had I sternly refused, you would perhaps have thought better of my book. Every single slip is greatly altered & I hope improved.—

With respect to the human ovule, I cannot find dimensions given, though I have often seen the statement.6 My impression is that it wd. be just or barely visible if placed on clear piece of glass.— Huxley7 could answer your question at once.— I have not been well of late, & have made slow progress, but I think my book will be finished by middle of November.

Yours affectionately | C. Darwin

LS(A)

1
The year is established by the reference to Lyell’s comments on the proof-sheets of Variation (see n. 3, below).
2
Lyell’s letter has not been found.
3
CD refers to Lyell’s comments on the proofs of Variation; Lyell had received the proofs around the end of July (see letter to Charles Lyell, 18 July [1867], and letter from Charles Lyell, 4 August 1867). In the published version, the last sentence of chapter 23 reads, ‘Hence, although it must be admitted that new conditions of life do sometimes definitely affect organic beings, it may be doubted whether well-marked races have often been produced by the direct action of changed conditions without the aid of selection either by man or nature’ (Variation 2: 292).
4
See Variation 2: 278–85.
5
In Origin, p. 132, CD had written, ‘How much direct effect difference of climate, food, &c., produces on any being is extremely doubtful. My impression is, that the effect is extremely small in the case of animals, but perhaps rather more in that of plants.’ In the third and fourth editions, the words ‘perhaps rather’ were deleted (see Origin 3d ed., p. 149, and 4th ed., p. 158). When the fifth edition was published in 1869, after the publication of Variation, the sentences read, ‘It is very difficult to decide how far changed conditions, such as of climate, food, &c., have acted in a definite manner. There is some reason to believe that in the course of time the effects have been greater than can be proved to be the case by any clear evidence’ (Origin 5th ed., p. 166).
6
A human egg cell is about a tenth of a millimetre in diameter. In Variation 2: 2, CD refers to ‘male or female sexual cells, which are so minute as not to be visible to the naked eye’.

Manuscript Alterations and Comments

1.3 (you … “often”)] interl
1.5 in these two respects 1.6] altered from ‘in this respect’
1.8 which] interl
1.9 And … conditions. 1.10] inserted
2.1 (& … mention)] interl
3.3 perhaps] interl
3.3 & … Darwin 5.1] in CD’s hand
4.2 or barely] interl

Please cite as “DCP-LETT-5640,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-5640