In some very real sense violence is embodied in the human genetic/evolutionary legacy as is evidenced by its frequent manifestation in the human species as well as in others. Although the complex outcomes of the interactions of genetic predispositions with the social, ecological and cultural environments are themselves not embodied in the genetic makeup, nevertheless any violent species-specific behaviour is part of its evolutionary heritage to the extent that any such cultural heritage forms a continuum with the biological heritage.
In 1993, researchers from the Netherlands and the USA reported that in one large family they have linked a small genetic defect with impulsive, hostile and violent behaviour in the males. Those afflicted often reacted to the most mildly stressful occasions with aggressive outbursts, shouting at, cursing or assaulting the person they deemed a threat. At other times the men have committed arson, attempted rape and exposed themselves in public. In addition, their intelligence is on the low end of normal, with an average IQ of around 85 to 90. The abnormal behaviours are linked to the gene responsible for the production of monoamine oxidase-a, an enzyme which destroys neurotransmitters in the brain.
Violence lies in the animal brain and instincts of humanity. Physiological research has described many of its mechanisms, while the law, anticipating science, has in many countries recognized its involuntary nature, and exonerated certain crimes such as justifiable homicide (as in the case of self-defence) and some crimes of passion or even crimes avenging insulted dignity or 'honour'. War is a natural human instinct. Man is therefore condemned by biology to war.
In the course of human evolution there has been a selection for aggressive behaviour more than for other kinds of behaviour. The human species has inherited a tendency to make war from its evolutionary ancestors and consequently war and other forms of violent behaviour are genetically programmed into human nature.
It is incorrect to claim that war or any other violent behaviour has been genetically programmed. While genes are involved at all levels of nervous system function, they provide a developmental potential that can be actualized only in conjunction with the ecological and social environment. Except for rare pathologies, genes do not produce individuals necessarily predisposed to violence. Neither do the determine the opposite.
It is incorrect to claim that in the course of evolution there has been a selection for aggressive behaviour more than for other kinds of behaviour. In all well-studied species, status within the group is achieved by the ability to cooperate and fulfil social functions relevant to the structure of the group. "Dominance" involves social bondings and affiliations; it is not simply a matter of the possession and use of superior physical power, although it does involve aggressive behaviours. Where genetic selection for aggressive behaviour has been artificially instituted in animals, it has rapidly succeeded in producing hyper-aggressive individuals; this indicates that aggression was not maximally selected under natural conditions. Violence is neither in the evolutionary legacy nor in the genetic makeup.
It is incorrect to claim that humans have a "violent brain". While we do have the neural apparatus to act violently, it is not automatically activated by internal or external stimuli. Like higher primates and unlike other animals, the human neural processes filter such stimuli before they are acted upon. How people act is shaped by how they have been conditioned and socialized. There is nothing in neurophysiology that compels humans to react violently.
It is incorrect to claim that violence or war is caused by "instinct" or any other single motivation. The emergence of modern warfare has been a journey from the primacy of emotional and motivational factors, sometimes called instincts, to the primacy of cognitive factors. Modern war involves institutional use of personal characteristics such as obedience, suggestibility and idealism, social skills such as language, and rational considerations such as cost calculation, planning and information processing. The technology of modern war has exaggerated traits associated with violence both in training of actual combatants and in the preparation and support for war in the general population. As a result of this exaggeration, such traits are often mistaken to be the causes rather than the consequences of the products.