Final answer:
Aggression is behavior that is intended to cause harm or pain. Humans engage in aggression when they seek to cause harm or pain to another person. Aggressive displays in the animal kingdom are a mechanism to assess the fighting ability of opponents.
Step-by-step explanation:
Aggression
Aggression is behavior that is intended to cause harm or pain. It may involve physical violence against other individuals. For example, two male gorillas may fight and use their canine teeth to inflict deep wounds. Expressing aggression this way may lead to serious injury and even death.
Humans engage in aggression when they seek to cause harm or pain to another person. Aggression takes two forms depending on one's motives: hostile or instrumental. Hostile aggression is motivated by feelings of anger with intent to cause pain; a fight in a bar with a stranger is an example of hostile aggression. In contrast, instrumental aggression is motivated by achieving a goal and does not necessarily involve intent to cause pain (Berkowitz, 1993); a contract killer who murders for hire displays instrumental aggression.
The topic of human aggression has received a great deal of attention from academics. Some have argued that there is an innate aggressiveness in humankind towards other humans, especially in the case of males. According to one school of thought, this aggressiveness builds up in the individual until it finds a behavioural outlet. Others argue that it is culture that determines whether humans behave aggressively towards one another. The view taken here is that, while humans are not 'innately aggressive', there is an innate tendency for people to behave aggressively in response to perceived threats to themselves or to their in-group. Cultural factors have an important influence on what is, and what is not, perceived as a threat. Aggressive behaviour can also be a consequence of cultural pressures in societies in which aggression and violence are seen as criteria for praise and approval.
Aggressive displays are also common in the animal kingdom. An example is when a dog bares its teeth when it wants another dog to back down. Presumably, these displays communicate not only the willingness of the animal to fight, but also its fighting ability. Although these displays do signal aggression on the part of the sender, it is thought that these displays are actually a mechanism to reduce the amount of actual fighting that occurs between members of the same species: they allow individuals to assess the fighting ability of their opponent and thus decide whether it is 'worth the fight.' The testing of certain hypotheses using game theory has led to the conclusion that some of these displays may overstate an animal's actual fighting ability and are used to 'bluff' the opponent. This type of interaction, even if 'dishonest,' would be favored by natural selection if it is successful more times than not.