In Seville, Spain in 1986 a group of scientists met to explore the sources of human aggression. John E. Mack explains the results of the Seville Statement of Violence:
In the Seville Statement the signatories, who included psychologists, neuroscientists, geneticists, anthropologists, and political scientists, declared that there was no scientific basis for considering human beings innately aggressive animals, inevitably committed to war on the basis of biological nature. Rather, they said, war is a result of socialization and conditioning, a phenomenon of human organization, planning, and information processing that plays on emotional and motivational potentialities. In short, the Seville Statement implies that we have real choices and that a new kind of responsibility in the conduct of human group life is possible.
(John E. Mack, 'The Enemy System', in Vamik Volkan, et al eds., The Psychodynamics of International Relationships: Volume I: Concepts and Theories. Lexington, MA, Lexington Books, 1990, p. 58.)
The full statement is in a UNESCO pamphlet 1989 http://www.culture-of-peace.info/brochure/titlepage.html
See also http://www.culture-of-peace.info/ssov-intro.html including David Adams and Sarah Bosch, "The Myth That War Is Intrinsic to Human Nature Discourages Action for Peace by Young People"
This discussion is particularly relevant to causes of genocide, and the climate wars predicted by Gwynne Dyer