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Darwin Correspondence Project

From George Henslow   22 February 1869

St. Johns Parsonage | S. Johns Wood | N.W.

Feb 22d/69

Dear Mr Darwin

I have got an idea which I am endeavouring to support by collecting materials of various kinds, & I take the liberty of writing to you to ask if you can assist me. It is this.— that mimetic forms of animals have arisen through the direct cause of prenatal impressions received through the sense of sight; & aided by natural selection.

The grounds for this idea are these

1) the human fœtus is frequently affected by the sight of objects which produce shocks upon the mother.— this is pooh-poohed by many but I think, I have succeeded in establishing it, nevertheless.1

2d) Cases amongst animals   a cow A pregnant by Bull B is, however, kept in a field with C (Bull or Cow or Bullock) The result is that the calf may resemble C more than B.

Virgil states somewhere, but have not to hand to refer that if a mare is to bring forth a particular color place such a colored animal before her while being covered by the stallion.—2

compare Jacob’s rod.—3 &c &c

Now I want to collect cases from Breeders of cattle, if possible; & knowing from yr writings that you had many communications from them on other points,—I was anxious to know if they stated anything to the above effect. & if so whether you would kindly let me hear it.

No case where Pangenesis could apply is of any use. For I want to try & substantiate my idea, where there has been no connection at all: no hereditary descent &c. &c all of which cases would be explained by Pangenesis.4

If you have no instances to refer to, could you oblige me with the names & addresses of those breeders with whom you have had correspondence? You will see that my idea is that in consequence of animals constantly living in the same localities & surrounded by the same objects generation after generation; the fœtus has by the slow accumulation of mental force—gradually become assimilated in form or appearance to the surrounding objects.—

Yrs very truly | Geo Henslow


The ancient belief in the effect of maternal imagination on the development of the foetus was well established by the early eighteenth century, when it was used to account for a wide variety of malformations (D. Todd 1995, pp. 47–52). For more on popular belief in the effect of maternal imagination, see Huet 1993, D. Wilson 1993, and D. Todd 1995. For CD’s scepticism on the topic, see Correspondence vol. 16, letter to J. J. Weir, 18 April [1868].
Virgil discusses horse breeding in book 3 of the Georgics, but the reference has not been identified.
Henslow refers to the biblical account of Jacob’s placing speckled rods before sheep so that the offspring would be speckled (see Gen. 30: 37–9).
CD published his provisional hypothesis of pangenesis in Variation 2: 357–404. CD suggested that minute particles (gemmules) circulated in the bodily fluids and were capable of generating new cells, remaining dormant until required. He thought his hypothesis could explain both sexual and asexual reproduction, as well as reversion and the regrowth of body parts. For CD’s discussion of pangenesis with correspondents, see, for example, Correspondence vol. 13, letter to T. H. Huxley, 27 May [1865], and Correspondence vol. 14, letter to J. D. Hooker, 4 April [1866].


Asks CD for references to animal breeders in order to test the hypothesis that mimicry arises through direct action of mental impressions received through the sense of sight.

Supports natural selection and Pangenesis.

Letter details

Letter no.
Henslow, George
Darwin, C. R.
Sent from
St John’s Wood
Source of text
DAR 166: 168
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 6626,” accessed on 26 February 2017,