In psychology, the term aggression refers to a range of behaviors that can result in physical and psychological harm to oneself, others, or objects in the environment. Aggression can take many forms, including: physical, verbal, mental and emotional. Aggression can also serve a number of different purposes, such as asserting dominance, intimidating or threatening, or expressing anger or hostility. Everyone has experienced anger at some point in our lives, and some of us have channeled that anger into violence, perhaps throwing a punch during a heated argument or after too many beers at the bar. . Then there are attacks on a larger scale, in the form of murders, wars and genocides. Trying to understand what fuels different levels of human aggression, from fistfights to nation-on-nation fighting, has long preoccupied human biologists. Through research, it has become clear that human aggression is not simply "bad behavior" and that impulsive aggression is problematic. can be considered an identifiable behavioral disorder with genetic, biological and therapeutic correlates. This research has occurred through animal studies involving lower and higher order non-human subjects and clinical research with humans. Animal research has often led to work on human populations. Research into the biology and treatment of human aggression has revealed that biological substances, such as neurotransmitters and hormones, are capable of inhibiting or facilitating aggression in lower animals. Aggression in humans and animals has been associated with serotonergic function (Bethea, Reddy, Robertson, & Coleman, 2013). Serotonin is known as nature’s “feel good” chemical. It is the most widely distributed and most studied neurotransmitter in the middle of the article...... an aggressive social encounter can cause changes in the brain that lead to depression, anxiety and susceptibility to the immune system. related diseases. Surprisingly, animal research shows that abusers can suffer many of these same effects. Aggressive encounters increased circulating levels of stress hormones in both dominant and submissive mice, suggesting that aggression affected both groups equally. Chronic exposure to social stress increased susceptibility to bacterial infection in both groups, but more so in dominant mice than in submissive mice. Unlike most behaviors, individual acts of increased aggression and violence have the potential to impact society as a whole. Research, from fruit flies to humans, is helping to decipher the biological causes of these abnormal behaviors. This research promises to reveal new avenues for treatment and prevention in the years to come.