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Show 24.2 SEXUAL SELECTION : l\:IA~11\1ALS. PAin' ll. of tho walrus the tusks are sometimes quite absont. 4 In the malo elephant of Incba and in tho male dugoBg 5 the upper incisors form offensive weapons. In the n:alc narwhal one alone of the upper teeth is develope~ mt.o the well-known, spirally-twisted, so called hor?, wh~ch IS sometimes from nine to ten feet in length. It IS believed that the males use these horns for fighting together; for '' an unbroken one can rarely be got, and occa.sionally "one may be found with the point of another Jamm?d " into the broken place.'' 6 The tooth on the opposite side of the head in the male consists of a rudiment about ten inches in length, which is embedded in the jaw. It is not, however, very uncommon to find double-horned male walruses in which both teeth arc well developed. In the females both teeth are rudimentary. The male cachalot has a larger bead than that of the female, and it no doubt aids these animals in their aquatic battles. Lastly, the adult male ornitborbynchus is provided with a remarkable apparatus, namely a spur on the fore-leg, c;lo ely resembling the poison-fang of a venomou~ snake; it use is not known, but we may suspect that It serves <tS a weapon of offence.7 It is represented by a mere rudiment in the female. \Vben the males are provided with weapons which the females do not possess, there can hardly be a doubt that they are used for fighting with other males, ~nd that they have been acquired through sexual selection. 4 1\lr. Lmnont ('Seasons with the Sea-Horses,' 1861, p. ~43) says th11t a good tusk of the moJo walrus weighs 4 pounds, und 1s lougcr than that of the female, which wEdghi:! about 3 pounds. Tho males arc described as fighting ferociously. On the occosional abscnco of the tusks in the female, see Mr. H. Brown, 'Proc. Zool. Soc.' 1868, P· 429. l Owen, 'Anatomy of Vertebrates,' vol. iii. p. 283. o Mr. R. Brown, in' Proc. Zool. Soc.' 1869, p. 553. 1 Owen on the Cachalot and Ornithorhynchus, ibid. vol. iii. p. 638, Gil. CIIAP. XVII. LAW OF BATTLE, 243 It is not probable, at least in mo~t cases, that the females ha:c actuall~ be~n saved fi-om acquiring such weapons, owm~ ~o ~heir Lemg useless and superfluous, or in some way IDJurwus. On the contrary, as they are often used by the ma!es of many animals for various purposes, more e~~eCially as a defence against their enemies, it is a s:uprismg ~act that they are so poorly developed or qmte absent m the females. No doubt with female deer the cle~elopment during each recurrent season of great branclnng h?rns, and with female elephants the development o~ 1mmense tusks, would have been a great waste of v1tal power, on the admission that they were of no. use to the females. Consequently variations in the SIZe of these organs, leading to their suppression would have come under the control of natural selection' an~ if limited in their transmission to the female offsprmg would not have interfered with their development .thr?ugh sexual selection in the males. But how on th1s v1ew can we explain the presence of horns in the females of certain antelopes, and of tusks in the females of m~ny animals, which are only of slightly less size than m the males? The explanation in almost all cases must, I belie.ve, be sought in the laws of transmission. A.s the remd~er is the single species in the whole family of Deer m which the female is furnished with horns, though somewhat smaller, thinner, and less branched than in the male, it might naturally be ~~ough.t that they must be of some special use to her. lhere 1s, however, some evidence opposed to this view rrbe female retains her horns from the time when the; are fL~lly devel?ped, namely in September, throughout the. wmter, until May, ':"hen she brings forth her young; wh1lst the male casts his horns much earlier towards the end of November. As both sexes have the ~arne requirements and follow the same habits of life, and as the male R 2 |