SEXUAL SELECTION 173 



with which nothing must interfere, and in most species one 

 parent alone cannot undertake the task. When young birds are 

 "precocious," i.e. able to run about directly they are hatched, 

 and, under maternal direction, to pick up food for themselves, 

 then polygamy becomes general. The moor-hens might seem to 

 be an exception to the rule, since the young when born have 

 the use of their legs and faculties, yet both parents and even 

 their brothers and sisters of a previous brood help to rear them. 

 But this exception helps to prove the rule, since the "precocity" 

 of the moor-hen does not enable him to forage under water. 

 We may rank the moor-hen, therefore, with the species in which 

 the young are born helpless and remain long in the nest before 

 they venture forth into the world. And it is in such species that 

 we find that the' cock is a faithful husband and helps the hen in 

 foraging. The mallard is attentive to his mate during at least 

 part of the time of incubation. As soon as or before it is over, 

 his moulting begins and, his power of flight being lost for the 

 time, he retires for safety to the water. When the young ducks 

 hatch out, the mother unassisted tends them. However, as they 

 are undoubtedly " precocious," what we have to account for is 

 the persistence of monogamy. Probably the hen has to be long 

 absent from the eggs in order to obtain sufficient food and then 

 the mallard may sit in her place. When ducks are domesticated 

 the food difficulty is removed and they readily take to polygamy. 

 Partridges are no exception to our rule, for the cock-bird helps 

 much in tending the young and protecting them from birds of 

 prey. 



Among mammals the principle is the same. The young of 

 the great ruminants are able to browse on grass or young 

 shoots of trees as soon as they are weaned. And among 

 ruminants polygamy exists on a very large scale. Among the 

 terrestrial carnivora, on the contrary, 1 the lion is believed to be 

 the only polygamist, and even he sometimes lives with only one 

 female, never, apparently, with more than five. Here, as always, 

 the system is maintained by fighting, and his lordly mane is use- 



1 See Darwin's Descent of Man, vol. i. p. 268. Much information on the 

 subject of polygamy among animals is to be found in this work. 



