kcaj_123
Not so new Member
I assume this has been said due to my previous comment? I'll assume it is so i can comment.
Males and males do kill each other. They are called fighting fish because of this. The fancy strains that we see today however have not been breed for fighting abilities. They have been breed for colour, fin lenth, breeding capabilities etc. An overly aggressive male has no place in a breeding facility as breeders do not want to risk the females being killed. So the aggressive gene cannot be passed on. You do get exceptions to this very broad idea but you also get alot of male fighters that follow this idea and don't really know they are meant to kill each other. Hence you can sometimes keep some males together.
The selective breeding has not undone millions of years of evolution, contrary to what you seem to believe.
Put a divider between two males so they cannot see eachother for a few days and then pull the divider out... VOILA extreme flaring and aggression. Put them in the same tank and they will rip eachother to pieces.
Selective breeders try to minimise of the male, but if he's good looking they will keep on trying to breed him and so can lose 3 or so females in the process. There are tricks employed to try and reduce aggression but they will not discard the idea or plan of breeding him just because he is aggro.