98 IOWA ACADEMY OF SCIENCES. 



sense used in this paper, (c) The males tight fiercely for the possession of 

 the females. 



Erignathus harbatus (Bearded Seal), (a) Considerable sexual disparity'. 

 Length of male, 10 feet; length of females, 7 feet 4 inches. Weight of males, 

 two and one-half times that of females, ib) Strictly polygamous, according 

 to the single authority found, (c) Males often have severe battles, the 

 strongest males driving away the younger. 



Macro7iiinus angustirostris (Sea Elephant), (a) Great sexual disparity. 

 The weight of the male is three and one-half times that of female, {b) Polyg. 

 amous.4 Elliott says that they "resemble the sea lion in their breeding 



Eumetopias stelleri (Steller's Sea Lion), [a] Great sexual disparity. Length 

 of males, 12 feet; of females, 8i feet. Weight of male, three times that of 

 female, ib) Strictly polygamous. This species inaiutains a regular harem, 

 l)ut "does not maintain any such regular system in preparing for and atten- 

 tion to its harem as is illustrated on the breeding grounds of the fur seal '> 

 (Elliott), (c) "The bulls fight savagely among themselves, and turn off 

 from the breeding ground all the younger and weak males." 



Callorhinus ursinus (Northern Fur Seal), (a) Extreme sexual disparity. 

 The males weigh three times as much as the females, (b) Ulti-a polygamous, 

 the males maintaining a large harem, and guarding the females with the 

 greatest vigilance and courage. In fact, this animal is the most polygamous 

 of all the Mammalia, (c) Males tight with greatest desperation and persist- 

 ence for females. 5 



A consideration of the above series will disclose the fact that there is a 

 close and constant relation between polygamy and disparity in size among 

 the Pinnipedia. It also indicates that this relation is a direct one, the dis- 

 parity increasing pari 2)Cissu with the polygamy throughout the series. 

 Another fact is rendered evident by this series, and that is that the com- 

 bativeness of the males increases part passti with sexual disparity and 

 polygamy. 



These facts having been reasonably well established, it is possible to con- 

 struct a hypothetical history of events which will illustrate the successive 

 stages by which a species might pass from a simply gregarious habit, in 

 which monogamy, or at least promiscuity, prevails, to the extreme of 

 polygamy practiced by the northern fur seal. Such a transition may be con- 

 ceived to take place by the following steps or gradations: 



1st. An eminently gregarious species would offer more favorable condi- 

 tions for the introduction of polygamy than a nongregarious species. Our 

 point of departure in this part of the discussion would then be a gregarious, 

 monogamous species. If the principles deduced from an examination of 

 the series presented in the first part of this paper be correct, this species 

 should also be one in which there is little sexual disparity, and little or no 

 fighting among the males for the posseession of the females. All of the 



4 "The sea elephants appear to be exceptional among the Phrocidte in the great dis- 

 parity of size between the sexes, in which, as well as in their hrceding habits, they closely 

 resemble the Otaries." Monograph of North American Pinnipeds (Allen), p. 755. The 

 Italics are mine. 



habits." [c) The males "fight desperately for the females." 



5 Elliott says he has seen one male fur seal fight fifty or sixty battles during a 

 single season. 



