Introduction ; V ariation. 
67 
female is also easily to be understood on the ground of the elimination of the 
disadvantageously coloured birds of this sex, yet the explanation does not seem 
to apply to the majority of cases, in many of which the female is like the male, 
and in others she is only a little less bright or wants some special marking 
and appears then to represent a lower stage in the history of the race, as the 
immature male is often like her. Many males assist in incubation. The female 
of the Cuckoo, Eudynamis, which lays its eggs in Crows’ nests does not appear 
to be protectively coloured, but the male, being black, might be thought to be so. 
Darwin’s theory of sexual selection has been much contested of late years. 
The author cites cases of certain female birds in captivity mating by preference 
with certain males and avoiding others; though allowance must perhaps be made 
for this in nature, there is now a strong opinion in favour of the view of a 
passive role being generally played by the female, the male expelling his rivals 
and making the female yield to him. 
There is much to be said for Mr. Wallace’s view of an excess of vitality 
or growth-force in the male as the cause of the development of superfluous 
decorative plumes, etc., though a localization of such growths in the skin “over 
centres of high nervous or muscular activity” is not tenable. For instance, the 
second primary of the male Macrodipteryx^ an African Nightjar, is developed 
into an enormous racket-feather capable of erection; three long racket-feathers 
sprout from each side of the head of the male of the Paradise-bird, Parotia, one 
very long one in Pteridophora, etc., etc. As the principal muscular and nervous 
centres are not different in birds, such a great diversity in the location of the 
accessory growths could not arise from this cause. Why does the male Paradisea 
have its ornamentation chiefly on the side of the breast, and another Bird of 
Paradise, Lophorhina, on the occipital region and jugulum? 
Mr. Wallace’s theory appears to include “the normal development of colour 
due to the complex chemical and structural changes ever going on in the 
organism” (Darwinism, p. 288), for the sex which possesses the most growth- 
force will be the first to undergo these necessary modifications. It is probable 
that a great number of sexual differences owe their origin to this developmental 
law. (See Loriculus^ antea p. 57). 
Mr. Stolzmann portrays the two sexes as naturally inimical to one another’s 
well-being. The males above a certain number are useless parasites, they diminish 
the food-supply and persecute the females; ill-fed females produce an excess 
of male offspring, and the female for her own preservation produces males which 
are disastrously equipped for the struggle for existence. We are unable to 
grasp the argument, if indeed it is a valid one, for it appears to us that the 
handicapped males will be the first to perish, and the males which will per- 
petuate the species will be the sons of females which produce the best-equipped 
offspring. Their qualities being inherited, these males will somewhat counteract 
the tendency on the part of certain females to produce inferior males, and the 
latter females will be less likely to survive than their sisters. As their inferior 
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