75© NATURAL SCIENCE. %^r 



stimuli, and the means of furnishing these stimuU are constantly 

 reproduced and improved by inheritance in the males." I further 

 admit that the display of ornament by the male is one of the means of 

 exciting this desire ; but mainly because it is an indication of sex, of 

 sexual maturity, and of sexual vigour, probably not at all on account 

 of details of colour or pattern. 



There is, however, another consideration which I\Ir. Cunningham 

 appears to have overlooked, and that is, the necessary weakness, 

 comparatively, of female selection, owing to the very limited range of 

 her choice. The law of survival of the fittest has such enormous 

 selecting power because of the overwhelming odds against the less 

 fit. A species which has two or three broods a year, or one large 

 brood, and which lives, say, ten or twenty years, as do many of the 

 vertebrata, produces from 50 to 100 successors of each pair, from 

 which one or two only are selected to take the place of their 

 parents. But in the case of sexual selection, it is a question of 

 probably not more than two or three to one in most species, and in 

 many even less, for there is no evidence and. little probability that 

 the number of healthy and competent males that fail to find mates 

 bears any large proportion to those that do find them. Much of the 

 success of particular males must depend on early chance encounters 

 with a mate, while the competition can only be among small groups 

 in each locality. If we add to this the consideration that in almost 

 every case combat, or agility, or bodily vigour must have great in- 

 fluence, the part that remains to be played by ornament alone will be 

 very small, even if it were proved, which it is not, that a slight 

 superiority in ornament alone usually determines the choice of a mate. 

 This, however, is a matter that admits of experiment, and I would 

 suggest that either some Zoological Society or any person having 

 the means, should try such experiments. A dozen male birds of the 

 same age — domestic fowls, common pheasants, or gold pheasants, for 

 instance — should be chosen, all known to be acceptable to the hen 

 birds. Half of these should have one or two tail plumes cut off, or 

 the neck plumes a little shortened, just enough to produce such a dif- 

 ference as occurs by variation in nature, but not enough to disfigure 

 the bird, and then observe whether the hens take any notice of the 

 deficiency, and whether they uniformly reject the less ornamented 

 males. Such experiments, carefully made and judiciously varied for 

 a few seasons, would give most valuable information on this interesting 

 question. Till this is done, suppositions as to what determines the 

 choice of the female can have but little value. 



Alkred R. Wallace. 



