86 CONTROLLED NATURAL SELECTION 
should be associated with great secondary 
sexual difference, and vice versa. 
In some animals, an excess of males is pro- 
duced by special methods, e.g. ants and bees. 
It appears not so much to ensure the fertili- 
sation of all females, as to render the chance 
of their destruction small. It is noteworthy 
that polygamy is usually associated with great 
secondary sexual differences ; these latter, ac- 
cording to the theory, give rise to great 
destruction of males, hence the association, 
as in the peacock. In predatory animals, 
polygamy is very rare; as are also great 
secondary sexual differences. 
If, as some maintain, the purpose of eye-spots in insects 
is to entice enemies to strike them, rather than more 
vulnerable parts: may not the eye-spots on the peacock’s 
(Pavo Cristatus) tail be to entice an enemy away from the 
female, to draw its attack ? 
When considering the parental colouring 
of birds, it will be noted that confinement of 
conspicuous colouring to the male is asso- 
ciated with open-nesting habits. It is possible 
that, among birds, conspicuous colouring con- 
fined to the male arose in this way (Wallace), 
and that afterwards it has become greatly 
evoluted by Natural Selection working with 
pairs. There is some evidence that open- 
