Aggression is something that is seen in all walks of life. In fact, it's one of the defining characteristics humans have in common with other species within the animal kingdom. Not to be confused with how a bird might kill a rat for its food source, aggression is an act of hostility that one animal displays in front of another animal when it feels threatened, challenged, or an immediacy to protect its territory.

While the cause of aggression in animals is mainly about food supply, land territory, and dominance, human beings can show aggressive behavior for a number of different reasons. Aggressiveness can also take a number of different forms, such as verbal, mental, or physical behavior. How aggression is displayed can also vary depending upon whether you're a man or woman. Men are much more likely to display aggression through physical violence, while women usually display aggression through nonphysical or indirect methods.

One common reason why people display aggression is in order to defend their personal space. Think of the brother and sister who are constantly at each other's throats because the younger sibling won't leave the teenage sibling alone and he certainly can't seem to stay out of her room. Or recall a situation where an acquaintance physically got too close to you during a conversation, in which you felt so crowded you had to take a few steps back.

Certainly human beings act aggressively toward anyone or anything that jeopardizes the well-being of their children, but when finances are compromised because of a mix-up at the bank or when a newly purchased, expensive appliance fails to operate properly after just a few days, things can get pretty heated between the parties involved. So humans not only have a need to protect their personal space and the safety of their children, but humans are very touchy when it comes to their hard-earned financial abundance (or lack thereof) as well.