€hap. VIII. 
SEXUAL SELECTION. 
271 
With respect to reptiles and fishes, too little is known 
of their habits to enable us to speak of their marriage 
arrangements. The stickle-back Gasterosteus), however, 
is said to be a polygamist ; 10 and the male during the 
breeding-season differs conspicuously from the female. 
To sum up on the means through which, as far as 
we can judge, sexual selection has led to the develop- 
ment of secondary sexual characters. It has been shewn 
that the largest number of vigorous offspring will be 
reared from the pairing of the strongest and best-armed 
males, which have conquered other males, with the 
most vigorous and best-nourished females, which are 
the first to breed in the spring. Such females, if 
they select the more attractive, and at the same time 
vigorous, males, will rear a larger number of offspring 
than the retarded females, which must pair with the 
less vigorous and less attractive males. So it will be 
if the more vigorous males select the more attractive 
and at the same time healthy and vigorous females ; 
and this will especially hold good if the male defends 
the female, and aids in providing food for the young. 
The advantage thus gained by the more vigorous pairs 
in rearing a larger number of offspring has apparently 
sufficed to render sexual selection efficient. But a lame 
o 
preponderance in number of the males over the females 
would be still more efficient; whether the preponder- 
ance was only occasional and local, or permanent; 
whether it occurred at birth, or subsequently from the 
greater destruction of the females ; or whether it in- 
directly followed from the practice of polygamy. 
The Male generally more modified than the Female . — 
Throughout the animal kingdom, when the sexes differ 
10 Noel Humphreys, ‘Kiver Gardens,’ 1857. 
