Male animal aggression during mating season. The evolutionary purpose of most species is to repopulate and keep the species alive long enough to become the highest being it can evolve into (We humans have done the best at this so far). So, every male in a species gets aggressive during mating season because the stronger ones are most likely to have healthy offspring. So, when animals fight they are fighting to keep their species alive. If you think about it who wouldn't want to be responsible for the evolutionary breakthrough that kept a species alive over thousands of years? hope this helped.
