This chapter examines the evolutionary origins of human dual capacity for intergroup lethal conflict and peaceful cooperation by analysing the likely traits of the last common ancestor of chimpanzees, bonobos, and humans (LCAC-B-H). Four competing models for the LCAC-B-H are evaluated: bonobo-like, gorilla-like, chimpanzee-like, and mosaic-like ancestors. This analysis shows that, at the current state of knowledge, we do not know what the morphological and behavioural traits of this last common ancestor were. Accordingly, the chapter further expands the temporal scope of analysis to examine key morphological and behavioural traits across apes during the Miocene epoch (~23–5.33 Ma), living non-human great apes, and early hominins, in order to distinguish traits that were likely ancestral to the LCAC-B-H from those derived characters that evolved within the hominin lineage. The chapter thereby reveals a dual pattern: the capacity for intense male–male aggression appears to be an ancestral trait inherited from Miocene apes (and earlier ancestors), as suggested by their canine size and morphology. At the same time, intergroup peaceful cooperation is an evolutionary innovation that emerged in the hominin lineage.