How language and agriculture promote culture- and peace-promoting norms

Humans are predisposed to form in-groups and out-groups that are remarkably flexible in their definition due largely to the complex language that has evolved in them. Language has allowed for the creation of shared "background stories" that can unite people who do not know each other. Second, the discovery of agriculture has resulted in the critical need to negotiate boundaries, a process that can lead to peace (but also war).