2 CONTROLLED NATURAL SELECTION 
On the other hand, the soma carrying the 
male germ cells, the male, discharges its 
germ cells before fertilisation, and therefore 
is at no time bisexual, as the female can be. 
For another reason, males are less valuable 
than females—because the male can fer- 
tilise a number of females; therefore fewer 
males than females are required by a species. 
Further, as the sexes at birth commonly are 
approximately equal, and the environment 
of a species is always limited, and a species 
is best off when it fills its environment with 
individuals capable of the greatest fer- 
tility ... it follows that males, when in 
excess of females, or when equalling them 
in number, or perhaps even when somewhat 
less numerous, must be less valuable than 
females. Besides a difference in the value 
of individuals according to sex, there is a 
difference according to age. 
A very old and sterile, or relatively sterile, 
individual is not only valueless but harmful 
to the species, in that it fills a place that a 
fertile individual should occupy. Young are 
more valuable than old, because they have 
a longer life for reproduction before them. 
There are other factors which give in- 
dividuals of a species differences in value, 
