228 THE EVOLUTION THEORY 



might have been endangered if the males had had to seek out the 

 females, which, in the ease of Bonellia, live in holes in the rocks on 

 the sea-floor, and, in the case of Trichosomuni, are concealed in the 

 urinary bladder of the rat. Obviously, this is the reason which, in 

 addition to the one already mentioned, has conditioned and produced, 

 or helped to produce, the remarkable minuteness of certain males. 



From another category of sexual differences we see in how many 

 ways species-selection and sexual selection play into each other's 

 hands. In many species of animals the males are eager for combat, 

 and they are equipped with special weapons, or excel the females in 

 general strength of body. As these males struggle, in the literal 

 sense of the word, for the possession of the females, Darwin referred 

 to sexual selection those distinguishing characters which gave the 

 stronger male the victory over the weaker, and thus raised the 

 victorious characters to the rank of general characters of the species. 

 And it certainly cannot be doubted that, for instance, the strength 

 and the antlers of the stag must have been increased through the 

 combats which recurred every year at the breeding season, for the 

 stronger always win in these battles. The case is the same with the 

 strength and the weapons of many other male animals. The lion is 

 effectively protected by his mane from the bite of a rival, and the 

 same protective arrangement occurs in quite a different family of 

 mammals^in an eared seal, which is called the .'sea- lion' for this 

 very reason. Among the seals the secondary sexual characters are often 

 very strongly developed, at least in all the polygamous species, for in 

 these the struggle for the females is very keen. In the ' sea-lions ' and 

 'sea-elephants' there are often fifty females to one male, and the 

 latter are 'enormously larger' than the females, while in mono- 

 gamous species of seal the two sexes are alike in size. 



Darwin has shown that actual combat for the females takes 

 place among most mammals, not only among stags, lions, and seals, 

 but even among the moles and the timid hares. Even among birds 

 such combats occur, and this is sometimes particularly noteworthy in 

 those species in which the males possess the most decorative colouring, 

 like the humming-birds. In some cases among birds there has also 

 been a development of weapons. Witness the spur of the cock, whose 

 merciless combats with his rivals Man has, as is well known, made 

 positively atrocious for his own amusement, by preventing the 

 flight of the vanquished. 



In Darwin's great work on sexual selection a considerable 

 number of cases are cited from among lower vertebrates, such as 

 crocodiles and fishes, and even from insects, in which the males fight 



