skip to content

Darwin Correspondence Project

From A. R. Wallace   24 February 1868

Hurstpierpoint, Sussex

Feb. 24th. 1868.

Dear Darwin

I am afraid I can give you very little definite information for it is astonishing how many questions may be asked about birds or butterflies, to which I cannot give the shadow of an answer.1

I am inclined to think that very few birds are truly polygamous, (like Gallus and a few other Gallinaceæ)   Nothing is known about the breeding of Birds of Paradise— The males are generally seen alone, except when they congregate to display their plumage. The females and young males go together. They may be polygamous, but I shd. think not. Plenty of Birds have strong sexual characters which decidedly are not polygamous, such as Cinnyridæ, Hornbills, Loriculus & Geoffroyus among Parrots, several of the fruit pigeons (Ptilonopus) besides all the Chatterers many with crests and appendages—2 I impute the absence of these characters in the females almost wholly to need of protection, for reasons set forth in my paper which will appear in No. 2. of the “Journal of Travel & Natural History”.3

I think it probable that the development of many or perhaps all of these characters may be aided by sexual selection or be wholly due to it,—but I think there is abundant evidence to prove that the cause of colour and fine plumage, (whatever it is) acts almost equally on both sexes as the rule; and that when these are wholly absent in the female, their absence has been produced by the need of protection, or by their being otherwise incompatible with the female’s parental duties.

I doubt if any male insects fecundate more than one female,—and I think it rather doubtful whether the female insect chooses the male; I think the male gets what female he can, and she submits to the first comer or to the strongest & swiftest, for insects certainly fight for the females. Colour in insects may be mainly produced by correlation with other parts of the organism. Thus, where the sexes of butterflies do not materially differ, the male is generally smaller stronger, a quicker flier, and more highly coloured.

It is not known if the Orang is polygamous. The males are generally seen alone.4 The females and young males in small parties.

I have no books here, or would look out for some evidence of polygamy in birds for you. I shall not be back to stay in town till July. Pray do not talk of troubling me. I am only too happy if I can give you any information, and I have plenty of time, for I work very easily,—only an hour or two a day.

I am in the 2nd. Vol. of your book, and I have been astonished at the immense number of interesting facts you have brought together— I read the chapter on Pangenesis first, for I could not wait.5 I can hardly tell you how much I admire it. It is a positive comfort to me to have any feasible explanation of a difficulty that has always been haunting me,—and I shall never be able to give it up till a better one supplies its place,—and that I think hardly possible.

You have now fairly beaten Spencer on his own ground, for he really offered no solution of the difficulties of the problem. The incomprehensible minuteness and vast numbers of the physiological germs or atoms (which themselves must be compounded of numbers of Spencer’s Physiological units) is the only difficulty,—but that is only on a par with the difficulties in all conceptions of matter, space, motion, force &c.6

As I understood Spencer, his physiological units were identical throughout each species, but slightly different in each different species;—but no attempt was made to show how the identical form of the parent or ancestors came to be built up of such units.

The only parts I have yet met with where I somewhat differ from your views, are in the chapter on the causes of variability,—in which I think several of your arguments are unsound: but this is too long a subject to go into now.

Also, I do not see your objection to sterility between allied species having been aided by natural selection.7 It appears to me that,—given a differentiation of a species into two forms each of which was adapted to a special sphere of existence,—every slight degree of sterility would be a positive advantage, not to the individuals who were sterile, but to each form. If you work it out, and suppose the two incipient species a … b to be divided into two groups, one of which contains those which are fertile when the two are crossed, the other being slightly sterile,—you will find that the latter will certainly supplant the former in the struggle for existence; remembering that you have shewn that in such a cross the offspring would be more vigorous than the pure breed, & therefore would certainly soon supplant them, and as these would not be so well adapted to any special sphere of existence as the pure species a and b, they would certainly in their turn give way to a and b.

I am sure all Naturalists will be disgusted at that malicious and ignorant article in the Athenæum. It is a disgrace to the paper, and I hope some one will publickly express the general opinion of it. We can expect no good Reviews of your book till the Quarterlies or best monthlies come out. I think the “Cambridge Man” of the “Darwinian Theory Examined” must have written for the Athenæum.8 I shall be anxious to see how “Pangenesis” is received.

Believe me | Yours very faithfully | Alfred R. Wallace

CD annotations

1.1 I am … answer. 1.3] crossed pencil
2.3 The males … History”. 2.10] scored blue crayon
3.1 I think … coloured. 4.7 crossed red crayon
3.2 there is … duties. 3.6] scored blue crayon
4.1 I think … the male; 4.2] scored blue crayon
4.5 Thus, … coloured. 4.7] scored blue crayon
5.1 It is … parties. 5.2] crossed blue crayon; double scored blue crayon
6.1 I have … troubling me. 6.2] crossed ink
9.1 As I … species, 9.2] double scored blue crayon
10.1 The only … now. 10.3] double scored blue crayon
11.1 Also, … existence,— 11.3] scored blue crayon


The family Cinnyridae is now known as Nectariniidae, sunbirds); Wallace misspelled Ptilinopus; chatterer is a common name for birds in the family Ampelidae, also known as waxwings. Wallace’s remarks on birds of paradise and chatterers are cited in Descent 1: 269.
Wallace refers to his paper ‘A theory of birds’ nests’ (A. R. Wallace 1868); CD’s annotated copy is in DAR 133: 12. See letter to A. R. Wallace, 22 February [1868] and n. 4.
In Descent 2: 361, CD stated that the male orang-utan was probably monogamous, but lived only part of the year with the female.
Wallace refers to Variation and to the chapter, ‘Provisional hypothesis of pangenesis’ (Variation 2: 357–404).
For a comparison between CD’s theory of heredity and that of Herbert Spencer, see the letter from Herbert Spencer, 8 February 1868 and n. 5.
CD discussed sterility in relation to natural selection in Variation 2: 185–9.
The Athenæum review of Variation was by John Robertson ([Robertson] 1868a). The Darwinian theory of the transmutation of species examined by a graduate of the University of Cambridge was by Robert Mackenzie Beverley ([Beverley] 1867).


[Beverley, Robert Mackenzie.] 1867. The Darwinian theory of the transmutation of species examined by a graduate of the University of Cambridge. London: James Nisbet & Co.

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

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

Wallace, Alfred Russel. 1868. A theory of birds’ nests: shewing the relation of certain sexual differences of colour in birds to their mode of nidification. Journal of Travel and Natural History 1 (1868–9): 73–89.


Responds to CD’s queries on polygamy in birds and orang.

Discusses sexual selection and secondary characters; colours and sexual preference.

Expresses his admiration for Pangenesis; it is superior to Herbert Spencer’s theory.

ARW differs somewhat with CD’s chapter on causes of variability [ch. 22 in Variation]. Thinks several of CD’s arguments are unsound.

Briefly discusses how natural selection might aid in producing sterility between allied species.

Letter details

Letter no.
Alfred Russel Wallace
Charles Robert Darwin
Sent from
Source of text
DAR 106: B70–2, DAR 86: A10–11
Physical description
ALS 9pp ††

Please cite as

Darwin Correspondence Project, “Letter no. 5922,” accessed on 9 February 2023,

Also published in The Correspondence of Charles Darwin, vol. 16