<P> In humans, there is good evidence that the basic human neural architecture underpinning the potential for flexible aggressive responses is influenced by genes as well as environment . In terms of variation between individual people, more than 100 twin and adoption studies have been conducted in recent decades examining the genetic basis of aggressive behavior and related constructs such as conduct disorders . According to a meta - analysis published in 2002, approximately 40% of variation between individuals is explained by differences in genes, and 60% by differences in environment (mainly non-shared environmental influences rather than those that would be shared by being raised together). However, such studies have depended on self - report or observation by others including parents, which complicates interpretation of the results . The few laboratory - based analyses have not found significant amounts of individual variation in aggression explicable by genetic variation in the human population . Furthermore, linkage and association studies that seek to identify specific genes, for example that influence neurotransmitter or hormone levels, have generally resulted in contradictory findings characterized by failed attempts at replication . One possible factor is an allele (variant) of the MAO - A gene which, in interaction with certain life events such as childhood maltreatment (which may show a main effect on its own), can influence development of brain regions such as the amygdala and as a result some types of behavioral response may be more likely . The generally unclear picture has been compared to equally difficult findings obtained in regard to other complex behavioral phenotypes . For example, both 7R and 5R, ADHD - linked VNTR alleles of dopamine receptor D4 gene are directly associated with the incidence of proactive aggression in the men with no history of ADHD . </P> <P> Humans share aspects of aggression with non-human animals, and have specific aspects and complexity related to factors such as genetics, early development, social learning and flexibility, culture and morals . Konrad Lorenz stated in his 1963 classic, On Aggression, that human behavior is shaped by four main, survival - seeking animal drives . Taken together, these drives--hunger, fear, reproduction, and aggression--achieve natural selection . E.O. Wilson elaborated in On Human Nature that aggression is, typically, a means of gaining control over resources . Aggression is, thus, aggravated during times when high population densities generate resource shortages . According to Richard Leakey and his colleagues, aggression in humans has also increased by becoming more interested in ownership and by defending his or her property . However, UNESCO adopted the Seville Statement of Violence in 1989 that refuted claims, by evolutionary scientists, that genetics by itself was the sole cause of aggression . </P> <P> Social and cultural aspects may significantly interfere with the distinct expression of aggressiveness . For example, a high population density, when associated with a decrease of available resources, might be a significant intervening variable for the occurrence of violent acts . </P> <P> Many scholars assert that culture is one factor that plays a role in aggression . Tribal or band societies existing before or outside of modern states have sometimes been depicted as peaceful' noble savages' . The ǃKung people were described as' The Harmless People' in a popular work by Elizabeth Marshall Thomas in 1958, while Lawrence Keeley's 1996 War Before Civilization suggested that regular warfare without modern technology was conducted by most groups throughout human history, including most Native American tribes . Studies of hunter - gatherers show a range of different societies . In general, aggression, conflict and violence sometimes occur, but direct confrontation is generally avoided and conflict is socially managed by a variety of verbal and non-verbal methods . Different rates of aggression or violence, currently or in the past, within or between groups, have been linked to the structuring of societies and environmental conditions influencing factors such as resource or property acquisition, land and subsistence techniques, and population change . </P>

Ways in which aggressive behavior affects a conflict situation