214 Evolution and Adaptation 
a few individuals, their perpetuation is not possible, since 
they will soon disappear through crossing. It would be, of 
course, preposterous to suppose that at any one time only 
those few individuals pair and leave descendants that have the 
secondary sexual characters developed to the highest point, 
but if something of this sort does not occur, the extreme of 
fluctuating variations cannot be maintained. Even if half 
of the individuals are selected in each generation, the accu- 
mulation of a variation in a given direction could not go 
very far. The assumption, however, that only half of all the 
individuals that reach maturity breed, and that all of these 
are chosen on account of the special development of their 
secondary sexual characters, seems preposterous. Further- 
more, if it is assumed that the high development of the new 
character appears in a large number of individuals, then it 
is not improbable that its continued appearance might be 
accounted for without bringing in, at all, the hypothesis of 
sexual selection. 
2. But even supposing that the females select the most beau- 
tiful males, then, since in the vast majority of higher animals 
the males and the females are in equal numbers, the others will 
also be able to unite with each other in pairs after this first 
selection has taken place. Nothing will therefore be gained 
in the next generation. It is interesting to see how Darwin 
attempts to meet this argument. He tries to show in the 
case of birds, that there are always unpaired individuals, but 
since the few facts that he has been able to collect show that 
there are as many additional females as males, the argument 
proves too much. A few species are polygamous, one male 
having a number of female birds; but on this basis we can 
only account, at best, for the development through com- 
petition of the organs of offence and defence used to keep 
away the weaker males. Yet it is just amongst these birds 
that we often find the ornamental characters well developed. 
In fact, since all the females in such cases are selected, and 
