SEXUAL SELECTION 213 



always one female to one male, there could be no choice exercised 

 either by male or female, for there would always remain individuals 

 enough of both sexes, so that no male need remain unmated. 



But this is not the case: the proportions of the sexes are very 

 rarely as i : i ; there is usually a preponderating number of males, 

 more rarely of females. Among birds the males are usually in the 

 majority, still more so among fishes; and among diurnal butterflies 

 there are often a hundred males to one female (Bates), although there 

 seem to be a few tropical Papilionidae among which the females have 

 rather the preponderance. Darwin called attention to the fact that 

 one could infer the greater rarity of the females even from the price- 

 lists of butterflies issued by the late Dr. Staudinger in connexion 

 with his business, for the females in most species, except the very 

 common ones, are priced much higher than the males, often twice as 

 high. In the whole list of many thousands of species there are only 

 eleven species of nocturnal Lepidoptera in which the males are dearer 

 than the females. 



Among the Mayflies or Ephemerides, too, the males are in the 

 majority; in many of them there are sixty males to one female: 

 but there are other kinds of insects, such as the dragon-flies 

 (Libellulidse), in which the females are three or four times as 

 numerous. There are also, it may be remembered, some kinds of 

 insects, such as Aphides, which have become capable of partheno- 

 genetic reproduction, and in which the males are becoming extinct, 

 e. g. in the case of Cerataphis in British orchid-houses. 



The first postulate implied in ' sexual selection,' namely, that 

 there be an unequal number of individuals in the two sexes, is there- 

 fore fulfilled in Nature ; we have now to inquire whether the second 

 condition postulated — the power of choice — may also be regarded 

 as a reality. 



This point has been disputed from many sides, and even by one 

 of the founders of the whole selection theory, Alfred Russel 

 Wallace. This naturalist doubts whether a choice is exercised among 

 birds by either sex in regard to pairing, and maintains that, even 

 if there could be a choice, this could not have produced such differ- 

 ences in colour and character of the plumage, since that would 

 presuppose the existence of similar taste in the females through 

 many generations. In a similar way it has been doubted whether 

 butterflies can be said to exercise any real power of sexual choice, 

 whether a more beautiful male is as such preferred to a less beautiful 



suitor. 



It must be admitted that direct observation of choosing is 



