106 CONTROLLED NATURAL SELECTION 
alike ; usually the male will be found 
to be conspicuous in one or more char- 
acters, as in song birds. 
In conclusion it may be said that many, if 
not the majority of those characters which 
distinguish males from females, are similar 
to the differences found between parents and 
young. 
Males equal females plus some other char- 
acters, females equal young plus some char- 
acters. In each case the added characters 
are alike, and according to the theory serve 
the same purpose. 
