"The human brain is among the largest relative to body size in mammals (Herculano-Houzel, 2009), but more surprising is that in the evolutionary time scale, the brain has recently (in the last million years or so) shown rapid increases in size (Adolphs, 2009). This poses a puzzle: why such a massive increase in such a relatively short time? One widely accepted answer to this puzzle is the social brain hypothesis (Adolphs, 2009; Byrne & Whiten, 1988; Whiten & van Schaik, 2007). This is the idea that the rapid development of the brain was in response to increases in the complexity of the social problems that were necessary for early hominids to solve. These problems include many of those we will review in this chapter: various forms of cooperation, deception, status hierarchy negotiation, altruistic punishment, and anticipatory fear of punishment. It is during this rapid spate of development that humans became a species able to enact a complex (im)morality"-- Provided by publisher.