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Darwin Correspondence Project

From Edward Blyth   [before 25 March 1868]1

Melanism. Among mammalia, perhaps peculiar (or nearly so) to the male sex in Felinæ,2 but not so in wolves and jackals. In some Marsupiata, as Phalangista and Phascolomys, apparently peculiar to the males, doubtfully so in the spotted Dasyuri, which latter should be seen to.—3 Among the sheath-horned ruminants, the deep black colour of this male of the Indian antelope (Cervicapra bezoartica) is peculiar to the rutting season, and disappears more or less afterwards. In castrated individuals of the Indian antelope, probably the Sable antelope (Ægoceros niger), certainly the nil-gai, and the banteng (Bos sondaicus), the colour remains as in the female;4 & Raffles remarks (in his History of Java) that in a castrated banteng the colour reverts to that of the female.5 In the nil-gai, the bluish-grey of the adult male is analogous; and I believe that Ant. leucophæa, auct. (supposed by some to have been extirpated) is merely the Ægoceros equinus, auct., in corresponding phase of colouring.6 N.B. The castrated nil-gai has small and slender horns, which are wanting in the females, and the castrated Indian antelope has horns like those which are very rarely developed in the female sex, being not spirally twisted (as in the entire males, but gyring round to the front with a tendency outwards.


They are longer and thicker than those which do sometimes occur in the female sex.

N.B. I cannot recal any instance in which the female sex undergoes a seasonal change of colouring among the mammalia. The Indian antelope is a strongly marked instance in the other sex, analogous to that observed in both sexes among the plovers and sandpipers in the bird class, black tern, &c. In the Gallicrex cristatus,7 the change in the males only is analogous to that of the Indian antelope.

Among wild birds, cases of true melanism are rare. The Corvus corone would seem to be no other than a permanent melanous race of C. cornix, & the familiar black crow of the Indo-China countries & of Ceylon to be an analogous race of the Indian C. splendens.8 In certain Falconidæ, one or both sexes become black with full maturity, as Spizaëtus limnäetus, Buteo sancti-Johannis, Astur melanoleucos(?), and Circus maurus.9 In the first-mentioned I am tolerably sure that both sexes become ultimately black.10 In the yellow orioles, both sexes are alike when fully mature, except that there is a slight greenish cast upon the back of the females, but the latter are slower in attaining this phase of plumage, probably not till the second or third moult.11 The same, I think, is the case with Lanius rufus, and more rarely with L. collurio, in which I have dissected a fertile female in the plumage generally considered to be peculiar to the male.12 Ditto in a hen common linnet, which had crimson poll and breast.13 Many black birds have brown or chestnut females, e.g. Turdus merula & kindred species, the Copsychi (more or less so), Saxicola opistholeuca, Pratincola caprata, Thamnobia fulicata, Campephaga aterrima, &c.14 The American Thamnophilinae have generally black or very dark ashy males & rufous females.15 Tetreo tetrix the different Kallij pheasants, Rollulus niger, Struthio camelus.16 In certain Hornbills, as Buceros nipalensis, B. plicatus, &c., and in the small fire-back pheasants (Euplocamus erythropthalmus & its Bornean congener), the female is wholly black, while the male is otherwise coloured; but this is the usual rule of brighter colours in the male sex, reversed in Rhynchæa & one or two other instances.17 Among the Picariæ, or non-passerine Insessores, difference of plumage in the sexes is rare, but we get it in several hornbills, trogons, [illeg] slightly in most woodpeckers (very strongly in Picus validus) and in the genus Eudynamis among the parasitic cuckoos, wherein the males are black & the females speckled.18 In some of the hornbills, as B. cavatus, the male has a crimson iris, the female a white iris, as in the storks of the genus Xenorhynchus the ♂ has a black iris, in the ♀ yellow.19 Perhaps the most striking seasonal sexual distinction among birds is instanced by the whidahs (Vidua), and the ruff perhaps next, but some few reeves have a slight development of the frill.20 Among the Rallidæ, in the genus Gallicrex, & I think also in the weka (Ocydromus) of New Zealand, the males only become deeply tinged with dark ashy (by a change of colour in the same feathers) during the breeding season, analogous to the black in the males of the Indian antelope.21 Among the Anatidæ we have several black males & br⁠⟨⁠own⁠⟩⁠ females, as notably the scoters (Oidemia).22 Sexual diversity of colouring is not usual among parrots, but occurs in the Platycercinæ, in Palæornis, Psittacula, Loriculus, and among the black cockatoos.23 Among pigeons, chiefly with the fruit-eaters, Treron & Ptilinopus, but a striking instance occurs in Turtur humilis.24 The female exceeds the male in size in the Falconidæ, Strigidæ, the Cassowaries, Apteryx, Cariama, & in the snipe and plover series (with the exception of the ruff).25 In the cranes, & in the herons, storks, & ibises, the male is larger. In some Turnices (as T. luzoniensis, T. pugnax), the female is larger, & is distinguished by more or less of black on the throat and breast, & in these the males are said to incubate;26 the same is probable of Rhynchæa, & certain of the cursorial birds, inclusive of Apteryx and also Tinamus.27 In the bustards, some have the males much larger, as Otis tarda, & the Eupodotis group, & these appear to be polygamous (like the ruff, and doubtless the Gallicrex among the Rallidæ the ♂ of which is 13 larger than the ♀). In O. tetrax the sexes are alike in size, but the male only is adorned during the breeding season.28 In the houbaras, I believe that both sexes are adorned, & they are of about the same size. In the florikens (Sypheotides) the female is larger, & the male only is adorned in the breeding season, while the sexual intercourse would appear to be indiscriminate.29 There is thus remarkable variation in the different forms of bustard. In Vulturidæ, & I think also Polyboridæ, the males are larger.30 In annulose animals generally the females are larger, but exceptions occur in Lucanus among the Coleoptera, & in various crabs and prawns (as notably in the large Indian Palæmon carcinus).31 I do not remember any mammal in which the female is larger, but there are instances both ways in Reptilia & Pisces.

The only secondary sexual distinctions which I can think of among the Primates, besides the beard &c in man, is that also of the orangutan, which again has much more formidable canines in the male sex. In some of the lemurs, the sexes are so different as to have been regarded as different species. Thus L. leucomystax is the female of L. nigrifrons, and again the black L. niger has a brown female. In L. catta & L. macaco the sexes are quite similar in colouring.32 In birds I know of no other case like that of Passer montanus, in which the young, as well as the adults of both Sexes, are clad in a plumage analogous to that characteristic of the adult male only of P. domesticus, while in other sparrows, as P. petronius, P. flavicollis, &c, both sexes retain the colouring analogous to that of the female and young of P. domesticus.33 In Rhynchea the young have the less brightly coloured plumage of the adult male. In Rhynchea it is also most remarkable that the female only of R. australis should have the excessively elongated trachea described by Gould, while the female of the (hardly distinguishable externally) R. bengalensis (few capensis)) has no elongation of the trachea whatever.34 In Platalea leucorodia the figure of 8 convolution of the trachea described by Yarrell is not of constant occurrence.35

—Have you anywhere worked in the fact that Palamedea is a goose, in which the web to the toes has quite disappeared? The semipalmate goose (Anseranas melanoleuca) makes a distinct approach to Palamedea in the peculiar shape of the bill as well as in the reduced palmature of the toes.36 Phœnicopterus is another most extraordinary modification of the goose type.—37

CD annotations

1.1 Melanism. … colouring. 1.12] crossed blue crayon
1.4 black colour 1.5] underl blue crayon
1.10 bluish-grey] underl blue crayon
2.1 N.B. … antelope. 2.5] scored and crossed blue crayon
3.1 The … maurus. 3.5] crossed blue crayon; ‘Birds’ added above blue crayon
3.8 but … moult. 3.9] scored blue crayon
3.24 the parasitic cuckoos] underl blue crayon
3.24 the males … speckled.] underl blue crayon
3.28 (Vidua)] underl blue crayon
3.28 ruff perhaps next] underl blue crayon
3.37 The female exceeds … series 3.38] scored red crayon
3.38 snipe and plover] underl red crayon
3.38 In the cranes, … larger 3.39] scored blue crayon
3.39 some Turnices] ‘Turnicesunderl red crayon; ‘Turnices’ added below blue crayon
3.43 In the bustards, … ♀ 3.45] scored blue crayon
3.45 O. tetrax] ‘Otis’ added below blue crayon
3.48 In the florikens] after cross red crayon; ‘see QQQQ QQQQ class’ pencil
3.48 the female … indiscriminate 3.49] scored blue crayon
3.50 forms of bustard. ] ‘Bustard’ added below blue crayon
3.51 In annulose] after opening square bracket blue crayon
4.3 In some … colouring. 4.6] scored blue crayon
4.7 as well] ‘CC’ added and del blue crayon
4.8 clad] ‘clad’ added blue crayon
4.14 In … occurrence.— 4.16] scored blue crayon, crossed pencil, ‘2’ added and circled pencil
Top of letter: ‘Blyth sexual selection mammals’ blue crayon


The date is established by the relationship between this memorandum and the letters to Edward Blyth, 25 March [1868] and 4 April [1868].
Felinae is a subfamily of the family Felidae and includes all but the big cats.
Marsupiata was the subclass of Mammalia now called Marsupiala. Blyth also refers to Phalangista, formerly a genus of possums, to Phascolomys, formerly a genus of wombats, and to Dasyurus, a genus of quoll. In Descent 2: 294, CD mentioned black varieties of wombat and ‘vulpine phalanger’, but cited Abraham Dee Bartlett for the information.
Hollow-horned or sheath-horned ruminants such as antelope have horns made of a permanent bony inner layer covered with an outer layer of keratin; these horns are never shed. Solid-horned ruminants such as deer have antlers made entirely of bone and shed their horns annually. Cervicapra bezoartica, a synonym of Antilope bezoartica, is now Antilope cervicapra (blackbuck). Aegoceros niger, a synonym of Antilope niger, is now Hippotragus niger. The nilgai is Boselaphus tragocamelus and the banteng is now Bos javanicus. In Descent 2: 288–9, CD cited Blyth for information on colour in Antilope bezoartica and A. niger.
In Raffles 1817, 1: 111, Thomas Stamford Bingley Raffles states that the banteng after castration invariably becomes red in colour. In Descent 2: 289, CD discussed colour in the banteng and colour reversion in castrated bulls.
Antilope leucophaea (now Hippotragus leucophaeus, the blue antelope or bluebuck) probably became extinct around 1800 (see Lichtenstein 1811, 1: 265). Blyth evidently believed it to be a colour variant of Aegoceros equinus; the name does not appear to have been published but probably refers to Hippotragus equinus, the roan antelope. In a letter of 24 February 1867 (Correspondence vol. 15), Blyth made a similar claim about the identity of the two species, incorrectly referring to the former as Aigoceros leucophaeus.
Gallicrex cristatus, the watercock, is now Gallicrex cinerea. For more on the change in colour in the male, see Correspondence vol. 15, letter from Edward Blyth, 24 February 1867.
The hooded crow, Corvus cornix, is now considered to be a separate species, although once considered a subspecies of C. corone (the carrion crow; see Clements 2000). Corvus splendens, the house crow, has a number of subspecies (Clements 2000).
Spizaetus limnaetusis a synonym of Nisaetus cirrhatus subsp. limnaeetus, the changeable hawk-eagle. Buteo sancti-johannis is a synonym of Buteo lagopus subsp. sanctijohannis, the rough-legged hawk. Blyth’s Astur melanoleucos is a synonym of Accipiter melanoleucus, the black goshawk. The genus Astur (goshawks; see Newton 1893–6, 2: 377) no longer exists; goshawks are now included in the genus Accipiter (Clements 2000). Circus maurus is the black harrier.
Spizaetus limnaetus has a dark form. For more on plumage variations in the species, see Birds of the world 2: 203.
The yellow auriole is Icterus nigrogularis. For more on plumage variations, see Hilty and Brown 1986.
For more on colour dimorphism in the sexes of Lanius rufus, the woodchat shrike, and L. collurio, the red-backed shrike, see Lefranc and Worfolk 1997.
Only the male common linnet (Linaria cannabina, referred to by CD in Variation 2: 158 as Linota cannabina) normally has the red colouring described by Blyth during the breeding season (see Greenoak 1997, pp. 207–8). In Descent 2: 180 and n., CD cited Blyth on cases where fertile females acquired male coloration.
Turdus merula: the blackbird. The genus Copsychus is the genus of shamas (Indian song-birds). Saxicola opistholeuca is now Oenanthe picata, the eastern pied wheatear. Pratincola caprata is now Saxicola caprata, the pied bushchat. Thamnobia fulicata is now Saxicoloides fulicatus, the Indian robin. Campephaga aterrima is now C. flava, the black cuckoo-shrike.
The Thamnophilinae (bush-shrikes) previously formed a subfamily of the family Formicariidæ, ant-thrushes (see Newton 1893–6, 1: 20). It is now a separate family, Thamnophilidae (antbirds). Blyth added this sentence along the left margin.
Tetrao tetrix is the black grouse. ‘Kalij’ was a name applied to several pheasants of the genus Euplocamus or Gallophasis (see Newton 1893–6, 2: 476). It now refers to the species Lophura leucomelanos, which has several subspecies. Blyth’s Rollulus niger is probably Rollulus rouloul, the crested partridge. Struthio camelus is the ostrich.
Buceros nipalensis (the rufous-necked hornbill) is now Aceros nipalensis; B. plicatus (Blyth’s hornbill) is now A. plicatus. Euplocamus erythropthalmus (the crestless fireback pheasant, now Lophura erythropthalma), has a Bornean subspecies. The genus Rhynchaea (painted snipes) is now called Rostratula.
The former order Picariae is roughly equivalent to the modern order Coraciiformes. Insessores: ‘The Perchers or Perching birds, having feet with three toes in front and one behind, adapted for perching on trees; the name given by Vigors in 1823 to the second Order of Birds in his classification, coinciding nearly with the Passeres and Picæ of Linnæus’ (OED). Picus validus (the orange-backed woodpecker) is now Reinwardtipicus validus. The genus Eudynamis is now Eudynamys.
Buceros cavatus (the great hornbill) is a synonym of B. bicornis cavatus. The stork genus Xenorhynchus is now Ephippiorhynchus; in E. asiaticus (the black-necked stork) males have dark brown eyes while females have yellow eyes (see Grimmett et al. 1998). In Descent 2: 129, CD cited Blyth for information on iris colour in B. bicornis and also mentioned colour differences in Xenorhynchus. Blyth used an upside-down female symbol instead of a male symbol.
Males of the genus Vidua (indigo-birds or whydahs) grow elongated tail feathers during the breeding season. In Descent 2: 181, CD mentioned plumage changes in Vidua. The ruff and reeve are the common names of the male and female respectively of Machetes pugnax (now Philomachus pugnax). CD discussed the plumage variations in Descent 2: 41–2, 81.
The family Rallidae are rails and crakes; the weka was Ocydromus australis, and is now Gallirallus australis.
The genus Oedemia (scoters; see Newton 1893–6, 3: 818), in the family Anatidae, is now Melanitta.
Platycercinae are broad-tailed parrots. The genus Palaeornis is now subsumed within the genus Psittacula (rose-ringed parakeets). Loriculus is the genus of hanging parrots; black cockatoos belong to the genus Calyptorhynchus.
Treron is the genus of green-pigeons; Ptilinopus is the genus of fruit doves; Turtur humilis is the red collared-dove, now Streptopelia tranquebarica.
Falconidae are falcons; Strigidae, owls. Cassowaries: Casuarius; Apteryx: kiwis; Cariama: seriemas, crane-like South American birds. Blyth probably refers to the former order Grallae or Grallatores, which included snipes and plovers (see Newton 1893–6, 2: 379–80). These birds are now placed in the order Ciconiiformes, (or sometimes Charadriiformes), with snipes in the family Scolopacidae and plovers in the family Charadriidae.
Turnix is the genus of button quails. Blyth’s T. luzoniensis is probably T. ocellata (the spotted button quail; see Ogilvie-Grant 1893, p. 548). Turnix pugnax (a synonym of T. taigoor) is now a subspecies of T. suscitator (the barred button quail). For more on the breeding habits of this genus, see Johnsgard 1991, pp. 41–2, 103. In Descent 2: 201, CD discussed the plumage of T. taigoor, but cited Blyth only concerning juvenile plumage.
The tinamou (Tinamus) is a partridge-like South American bird.
In Otis tarda, the great bustard, the average weight of the males can be three times that of the females (Johnsgard 1991, p. 127). Size differences in the sexes of species of the genus Eupodotis are not nearly as great (ibid., pp. 169–202). Otis tetrax, the little bustard, is now Tetrax tetrax (for sexual differences in this species, see ibid., pp. 117–19). Blyth used an upside-down female symbol instead of a male symbol in this text.
The houbara bustard is now Chlamydotis undulata. There are two species of florican: Houbaropsis bengalensis, the Bengal florican, and Sypheotides indica, the lesser florican. See also Correspondence vol. 15, letter from Edward Blyth, 24 February 1867 and n. 2.
The former family Vulturidae included all the old world vultures (see Newton 1893–6, 4: 1016). These are now in the family Accipitridae, which also includes hawks, eagles, and kites. Caracaras were formerly placed in a separate family, Polyboridae, by some authors, but are now in the family Falconidae (see Newton 1893–6, 1: 75).
The genus Lucanus (stag beetles) is now Pseudolucanus. The prawn species Palaemon carcinus is now Macrobrachium rosenbergii (the giant freshwater prawn).
Lemur leucomystax, L. niger, and L. macaco are now classified as Eulemur macaco, the black lemur. Lemur nigrifrons is now Eulemur mongoz, the mongoose lemur. Lemur catta is the ring-tailed lemur. In Descent 2: 290, CD discussed colour differences in male and female L. macaco.
Passer montanus is the Eurasian tree sparrow; P. domesticus, the house sparrow; P. petronia ‘petronius’ is a misspelling), the rock sparrow (a synonym of Petronia petronia); Passer flavicollis, the jungle sparrow (a synonym of P. pyrrhonotus). In Descent 2: 212, CD cited Blyth for information on plumage in sparrows.
Rhynchaea australis is a synonym of Rostratula australis, the Australian painted snipe; R. bengalensis and R. capensis are synonyms of Rostratula benghalensis, the greater painted snipe. Blyth refers to John Gould and to J. Gould 1865, 2: 275. CD scored the passage on the trachea in his copy of J. Gould 1865 (see Marginalia 1: 340). In Descent 2: 202–3, CD cited Blyth and Gould on the sexual differences in the trachea of these birds.
Platalea leucorodia is the white spoonbill; Blyth also refers to William Yarrell and Yarrell 1845, 2: 569–70. Yarrell noted that the convolution of the trachea was not always present in younger birds. In Descent 2: 60 n. 46, CD cited Blyth on the convolution of the trachea in spoonbills.
The genus Palamedea (now Anhima) has one species, Anhima cornuta, the horned screamer. Anseranas melanoleuca, the semipalmated goose, is now A. semipalmata, the magpie goose). Blyth had referred to the feet of these birds in his letter of 19 February 1867 (Correspondence vol. 15).
Phoenicopterus is the genus of flamingos.


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Clements, James F. 2000. Birds of the world: a checklist. Vista, Calif.: Ibis Publishing Company.

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.

Gould, John. 1865. Handbook to the birds of Australia. 2 vols. London: the author.

Greenoak, Francesca. 1997. British birds: their folklore, names and literature. London: Christopher Helm.

Marginalia: Charles Darwin’s marginalia. Edited by Mario A. Di Gregorio with the assistance of Nicholas W. Gill. Vol. 1. New York and London: Garland Publishing. 1990.

Newton, Alfred. 1893–6. A dictionary of birds. Assisted by Hans Gadow, with contributions from Richard Lydekker, Charles S. Roy, and Robert W. Shufeldt. 4 parts. London: Adam and Charles Black.

OED: The Oxford English dictionary. Being a corrected re-issue with an introduction, supplement and bibliography of a new English dictionary. Edited by James A. H. Murray, et al. 12 vols. and supplement. Oxford: Clarendon Press. 1970. A supplement to the Oxford English dictionary. 4 vols. Edited by R. W. Burchfield. Oxford: Clarendon Press. 1972–86. The Oxford English dictionary. 2d edition. 20 vols. Prepared by J. A. Simpson and E. S. C. Weiner. Oxford: Clarendon Press. 1989. Oxford English dictionary additional series. 3 vols. Edited by John Simpson et al. Oxford: Clarendon Press. 1993–7.

Ogilvie-Grant, W. R. 1893. Catalogue of the game birds (Pterocletes, Gallinae, Opisthocomi, Hemipodii) in the collection of the British Museum. London.

Raffles, Thomas Stamford. 1817. The history of Java. 2 vols. London: Black, Parbury and Allen, and John Murray.

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Yarrell, William. 1845. A history of British birds. 2d edition. 3 vols. London: John Van Voorst.


Detailed notes on secondary sexual differences in various species of birds and mammals.

Letter details

Letter no.
Edward Blyth
Charles Robert Darwin
Sent from
Source of text
DAR 83: 154–5, DAR 84.1: 131–3, DAR 48: A77, DAR 84.2: 187v
Physical description
Amem 4pp †

Please cite as

Darwin Correspondence Project, “Letter no. 6048,” accessed on 13 April 2024,

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