588 THE DESCENT OF MAN. 



cost of retarded fliglit, and other ornaments at the cost of 

 some loss of power in their battles with rival males. 



With mammals, when, as is often the case, the sexes 

 differ in size, the males are almost always larger and 

 stronger. I am informed by Mr. Gould that this holds 

 good in a marked manner with the marsupials of Aus- 

 tralia, the males of which appear to continue growing 

 until an unusually late age. But the most extraordinay, 

 case is that of one of the seals (Callorhinus ursinurs) 

 a full-grown female weighing less than one-sixth of a full- 

 gi'own male.* Dr. Gill remarks that it is with the polyg- 

 amous seals, the males of which are well known to fight 

 savagely together, that the sexes diifer much in size; the 

 monogamous species differing but little. Whales also 

 afford evidence of the relation existing between the pug- 

 nacity of the males and their large size compared with that 

 of the females; the males of the right- whales do not fight 

 together, and they are not larger, but rather smaller, than 

 their females; on the other hand, male sperm-whales fight 

 much together, and their bodies are ^^ often found scarred 

 with the imprint of their rivaFs teeth," and they are 

 double the size of the females. Tlie greater strength of 

 the male, as Hunter long ago remarked, f is invariably dis- 

 played in those parts of the body which are brought into 

 action in fighting with rival males for instance, in the 

 massive neck of the bull. Male quadrupeds are also more 

 courageous and pugnacious than the females. There can be 

 little doubt that these characters have been gained, partly 

 through sexual selection, owing to a long series of victo- 

 ries, by the stronger and more courageous males over the 

 weaker, and partly through the inherited effects of use. 

 It is probable that the successive variations in strength, 

 size, and courage, whether due to mere variability or to the 

 effects of use, by the accumulation of which male quadru- 

 peds have acquired these characteristic qualities, occurred 

 rather late in life, and were consequently to a large extent 

 limited in their transmission to the same sex. 



*See the very interesting paper by Mr. J. A. Allen in "Bull. Mus. 

 Comp. Zoolog. of Cambridge, United States," vol. ii, No. 1, p. 82. 

 The weights were ascertained by a careful observer, Capt, Bryant. 

 Dr. Gill in " The American Naturalist," Jan., 1871; Prof. Shaler on 

 the relative size of the sexes of whales, ''American Naturalist," 

 Jan. 1873. 



f ' Animal Economy," p. 45 



