The Making of Species 
Weir, who has carefully attended to the habits of 
birds during many years. There can also be no 
doubt that the most vigorous, best nourished, 
and earliest breeders would on an average 
succeed in rearing the largest number of fine 
offspring. The males, as we have seen, are 
generally ready to breed before the females ; the 
strongest, and with some species the best armed 
of the males, drive away the weaker; and the 
former would then unite with the more vigorous 
and better-nourished females, because they are 
the first to breed. Such vigorous pairs would 
surely rear a larger number of offspring than the 
retarded females, which would be compelled to 
unite with the conquered and less powerful males, 
supposing the sexes to be numerically equal ; and 
this is all that is wanted to add, in the course 
of successive generations, to the size, strength, 
and courage of the males, or to improve their 
weapons.” 
From this competition among the males there 
arise, firstly, contests between the males for 
mates; secondly, the preference of the females 
for favoured males. 
It is a matter of common knowledge that at 
the breeding season the males of nearly all, if 
not all, species are very pugnacious. Two 
males often engage in desperate fights for one 
or more females ; the victor drives away his foe 
and secures the harem. In such contests the 
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