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Darwin Correspondence Project

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

Footnotes

The year is established by the reference to Lyell’s comments on the proof-sheets of Variation (see n. 3, below).
Lyell’s letter has not been found.
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).
See Variation 2: 278–85.
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).
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’.
Thomas Henry Huxley.

Bibliography

Origin 3d ed.: On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. 3d edition, with additions and corrections. By Charles Darwin. London: John Murray. 1861.

Origin 5th ed.: On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. 5th edition, with additions and corrections. By Charles Darwin. London: John Murray. 1869.

Origin: On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. By Charles Darwin. London: John Murray. 1859.

Variation: The variation of animals and plants under domestication. By Charles Darwin. 2 vols. London: John Murray. 1868.

Summary

Replies to CL’s further comments [on Variation].

Discusses direct action of the environment as a cause of variation.

Letter details

Letter no.
DCP-LETT-5640
From
Charles Robert Darwin
To
Charles Lyell, 1st baronet
Sent from
Down
Source of text
American Philosophical Society (Mss.B.D25.334)
Physical description
4pp

Please cite as

Darwin Correspondence Project, “Letter no. 5640,” accessed on 27 February 2020, https://www.darwinproject.ac.uk/letter/DCP-LETT-5640.xml

Also published in The Correspondence of Charles Darwin, vol. 15

letter