552 THE DESCENT OF MAN. 



The fact of birds breeding in their immature plumage seems 

 opposed to the belief that sexual selection has played as important a 

 part, as I believe it has, in giving ornamental colors, plumes, etc., to 

 the males, and, by means of equal transmission, to the females of 

 many species. The objection would be a -alid one, if the younger 

 and less ornamented males were as successful in winning females and 

 propagating their kind, as the older and more beautiful males. But 

 we have no reason to suppose that this is the case. Audubon 

 speaks of the breeding of the immature males of JMs ta.dalus as a 

 rare event, as does Mr. Swinhoe, in regard to the immature males of 

 Oriolus.* If the young of any species in their immature plumage 

 were more successful in winning partners than the adults, the aduit 

 plumage would probably soon be lost, as the males would prevail 

 which retained their immature dress for the longest period, and thus 

 the character of the species would ultimately be modified.-} If, on 

 the other hand, the young never succeeded in obtaining a female, 

 the habit of early reproduction would perhaps be sooner or later 

 eliminated, from being superfluous and entailing waste of power. 



The plumage of certain birds goes on increasing in beauty during 

 many ytars after they are fully mature; this is the case with the 

 train of the peacock, with some of the birds of paradise, and with 

 the crests and plumes of certain herons, for instance, the Ardca 

 ludoxicana.^ But it is doubtful whether the continued development 

 of such feathers is the result of the selection of successive beneficial 

 variations (though this is the most probable view with birds of para- 

 dise) or merely of continuous growth. Most fishes continue increas- 

 ing- in size, as long as they are in good health and have plenty of 

 food; and a somewhat similar law may prevail with the plumes of 

 birds. 



CLASS V. , When the 'adults of loth sexes have a distinct winter 

 and summer plumage, whether or not the male differs from the 

 female, the young resemble the adults of both sexes in their winter 

 dress, or much more rarely in their .summer dress, or they resemble 



are blue and the young white; and white, mottled, and mature blue birds 

 may all be seen breeding together (vol. iv. p. 58); but Mr. Blyth !. -forms me 

 that certain herons apparently are dimorphic, for white and colored individ- 

 uals of the same age may be observed. The Harlequin duck (Anas histrionica, 

 Linn.) takes three years to acquire its full plumage, though many birds breed 

 in the second year ivol. iii, p. 014). The white-headed eagle (Falco leucoceplialvs), 

 vol. iii p. '210, is likewise known to breed in its immature ctate. Some species 

 of Oriolus uiceording to Mr. Blyth and Mr. Swinhoe, in " Ibis," July, ibG3, p. 

 38) likewise breed before they attain their 1'uil plumage. 



* See the last foot-note. 



t Other animals, belonging to quite distinct classes, are either habitually 

 or occasionally capable of breeding before they have fully acquired their 

 adult characters. This is the case with the young males of the salmon. 

 Several amphibians have been known to breed while retaining their larval 

 structure. Fritz Muller has shown (" Facts and Arguments for Darwin," 

 Eng. trans., 180!>, p. ?'.)) that the males of several amphipod crustaceans become 

 sexually mature while young; and I infer that this is a case of premature 

 breeding, because they have not as yet acquired their fully developed claspers. 

 All such facts are highly interesting, as bearing on one means by which species 

 may undergo great modifications of character. 



$ Jerdon, " Birds of India," vol. iii, p. 507, on the peacock. Dr. Marshall 

 thinks that the older and more brilliant males of birds of paradise have an 

 advantage over the younger males; see " Archives Neeiiandaises," torn, vi, 

 1871. On Ardea, Audubon. ibid, vol. iii, p. 139, 



