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 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
Detailed notes on secondary sexual differences in various species of birds and mammals.
- Letter no.
- Blyth, Edward
- Darwin, C. R.
- 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 27 March 2017, http://www.darwinproject.ac.uk/DCP-LETT-6048