would tend to resemble the husband of a former year ; and 
thus the object sought to be attained by strict selection 
would be frustrated. 
The form of marriage known as polyandry, in which 
one female has several husbands, would probably be fatal 
to the very preservation of a species. One method of 
exterminating rabbits, which is said to be found highly 
successful, is to trap as many as possible, kill off all the 
does that are caught, and let the bucks loose. “ The results 
of this mode of operation are that the male rabbits as soon 
as they begin to predominate in numbers, persecute the 
females with their attentions and prevent them from 
breeding. They also kill the young rabbits that happen 
to be born ; and even as Mr. Rodier asserts, when they 
largely predominate in numbers, worry the remaining 
does to death.”* These considerations serve to convince 
us that Sexual Selection cannot possibly supplement the 
deficiencies which may arise through any laxity in the 
action of Natural Selection. 
The theory then, contains in itself some striking diffi 
culties. Natural Selection can only act in adverse cir 
cumstances: it has to await the “accidental” emergence 
of favourable variations. If the isolation is strict, it is 
tremendously costly ; if it is not strict it is useless. Where 
Natural Selection is not strict, we have no right to assume 
that Sexual Selection will necessarily assist Natural Selec 
tion, and that the fittest variants will necessarily marry 
one another in preference to other less worthy survivors. 
* Nature, vol. xxxix., p. 493.