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Darwin Correspondence Project

From John Dean Caton   17 November 1870

Ottawa Illinois USA

Nov 17. 70

Dear Sir.

In my former answer to your inquiry about the difference in color of the male & female elk I expressed the opinion that the male is no darker than the female—1 I have now to make a partial correction of that statement. That report was made on observations made in the latter part of winter, and spring before the winter coat had been shed. Observations taken in the fall of the year, show that the darker portions, as the neck belly and legs of the male are very much darker than the female while on the sides and back the color on both is substantially the same— During the winter season these dark portions on the male fade out till in the spring they justify my former statement.2

I have also to correct a very important error into which I fell when writing “American Cervus”. I there stated that the elk sheds its coat but once a year.3 I have only discovered within the last few months, that in this I was mistaken, they certainly have a second peelage in the latter part of summer— The shades of color and the length of the hairs of the summer coat are so nearly identical with the new winter coat and the former disappears & is replaced by the latter so gradually, that it is exceedingly difficult to detect the change, even when attention is directly called to it—4 In only two specimens of my herd of 46 was it sufficiently distinct to arrest attention & then it required a months careful study to assure me of my former error

I have during 1869 & ’70 added to my collection live specimens both male & female, of the Mule deer (C. Macrotis) & Columbia Black Foot deer (C. Columbianus) Both upon which I am making careful observations which I shall embody in another paper5

It may interest you to state a very important physiological difference I have observed between the elk and the three smaller species which I have of that family—6 In the elk the theca extends forward along the abdomen to within three inches of the umbilicus & has no pendent prepuse almost precisely as is observed in the common bull,7 while with the three smaller species, the theca is suspended from a point so near the scrotum that when the animal is standing it occupies a vertical position not more than half an inch from that member. Its posterior measurement it is from 3 to 412 inches while anteriorly it is say two thirds that length. This lower portion may be considered an exagerated prepuse which as before stated is entirely wanting in the elk.8 I may attach undue importance to this marked distinction but it really seems to me to be quite worthy of observation

Upon fawns of the virginia deer I observe invariably, both male & female, a black spot at the place where the future horn is to appear on the male

On about five percent of the virginia deer when the winter coat first appears, a line of light colored spots appears on each side of the back, extending from the shoulder to the tail about five inches apart on the back but approaching each other towards the tail— Of these there are 16 between the shoulder & hips, and thence to the tail 5. These are more distinct on some specimens than on others and on but few can they be seen all the way back. Similar lines are always seen on the spotted fawn which although brighter in color are not so uniform in outline.9 Their exact uniformity in number whenever observed fixes them as a true characteristic of the animal

What gradual change may this animal be undergoing in this regard? Is there such a line of spots on the spotted deer of Europe? These spots entirely disappear in a month or six weeks. On one specimen I observed that the summer coat remained on the places of these spots when entirely gone on the regions surrounding them—

My virginia deer have so deteriorated in fertility that the number has diminished one half in four years, confirming your observations on the effect of domestication of many wild animals on their reproductive powers— I think however that a few of the original stock have constantly reproduced vigorous & fertile proginy which has continued through several generations, and I am not without hope of eventually rearing a stock from them, which will bare domestication, & remain vigorous & fertile—10 The gradual diminution in the growth of the horns through succeeding generations is quite observable.— The female virginia deer has four Mammae equally active, like the common cow. My observations of the other species, in this regard are not completed—

Audubons observations of the tuft of long course hares appearing on the brest of the aged female wild turkis will hardly hold good in this latitude. In all my own observations which embrace perhapes a thousand specimens. I have only seen it on the bird in my parks, on which it appeared when she was one year old. I have enquired of many hunters and of the game dealers of Chicago, who handle very many of these birds anually, and altogether have heard of but one other instance. I am persuaded therefore that this appendage is much more rare here than in Kentuckey 5 or 6 degrees further south where Audubon made his observations—11 My wild & domestic turkeys cross freely and the hybrids are very fertile12

When may we expect your new work?13 I am looking for it anxously

Yours very truly | J D Caton

Chas Darwin Esq

CD annotations

1.5 Observations … same— 1.7] scored blue crayon
5.1 Upon … male 5.2] ‘p. 359’ pencil, circled pencil
9.2 In all … fertile 9.9] scored blue crayon
Top of letter: ‘Colours of ♂ & ♀ elk | Spots on Deer | Hair on Turkey—’ blue crayon


For the discussion regarding the North American elk or wapiti (Cervus canadensis), see Correspondence vol. 17, letter to J. D. Caton, 20 March 1869, and letter from J. D. Caton, 5 May 1869.
See Caton 1877a, pp. 136 and 144–6; CD cited Caton for this information in Descent 2: 289. Caton had kept elk (Cervus canadensis), and other members of the deer family, in an enclosure since the early 1860s; see Caton 1877a, p. 78.
Caton’s paper on North American Cervus (Caton 1868) was also published in Caton 1880, pp. 146–75; for his discussion of the coat, see pages 148–9 and 152. An annotated offprint of Caton 1868 is in the Darwin Pamphlet Collection–CUL.
Caton described the discovery of his error in Caton 1877a, pp. 125–6.
For Caton’s description of the mule deer and the black-tailed deer, see Caton 1877a, pp. 93–6 and 97–9. Both deer (Caton’s Cervus macrotis and C. columbianus) are now Odocoileus hemionus; C. columbianus is sometimes classified as a subspecies, O. hemionus columbianus.
Caton refers to the mule deer, the black-tailed deer, and the common, Virginia, or white-tailed deer (Cervus virginianus, now Odocoileus virginianus).
Caton refers to the sheath, or theca, enclosing the penis, and the prepuce, or foreskin; see Caton 1877a, p. 269.
Caton 1877a, p. 270.
CD cited Caton for information on spots in adult Virginia deer in Descent 2: 303–4. When Caton described them in Caton 1877a, pp. 156–7, he noted that they had been overlooked by naturalists before Descent was published.
See Caton 1877a, pp. 304–8. For a reference by CD to decreased fertility in plants and animals removed from their natural habitat, see Origin, p. 9. CD also discussed the ‘evil effects of close interbreeding’ in Variation 2: 114–22, and discussed ‘The advantages and disadvantages of changed conditions of life; sterility from various causes’ in Variation 2: 145–72. See also letter from J. D. Caton, 5 May 1869 (Correspondence vol. 17).
See Correspondence vol. 17, letter from J. D. Caton, 5 May 1869, and letter to J. D. Caton, 24 May 1869 and n. 3. The references are to John James Audubon, and Audubon 1831–[9], 1: 15. In Descent 2: 180, n. 29, CD cited Audubon but also included Caton’s observation that females rarely acquired the tuft of hair.
See Caton 1877b.


Caton, John Dean. 1868. American Cervus. Read before the Ottawa Academy of Natural Sciences, 21 May 1868. Ottawa, Illinois: Osman and Hapeman.

Caton, John Dean. 1880. Miscellanies. Boston: Houghton, Osgood.

Correspondence: The correspondence of Charles Darwin. Edited by Frederick Burkhardt et al. 29 vols to date. Cambridge: Cambridge University Press. 1985–.

Descent: The descent of man, and selection in relation to sex. By Charles Darwin. 2 vols. London: John Murray. 1871.

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.


Observations on winter colour of coats of male and female elk,

spots on deer,

and tuft of hair on breasts of wild female turkeys.

Letter details

Letter no.
John Dean Caton
Charles Robert Darwin
Sent from
Ottawa, Ill.
Source of text
DAR 83: 172–4
Physical description
ALS 5pp †

Please cite as

Darwin Correspondence Project, “Letter no. 7375,” accessed on 1 October 2023,

Also published in The Correspondence of Charles Darwin, vol. 18