Groupishness is a tendency to commit prosocial acts for which the pathway to
compensatory fitness benefits is unpredictable. It is unique to humans, and its evolution is
not well understood. A difficulty is that the adaptive value of groupishness comes from
indirect reciprocity, which is hard to explain in societies that contain power asymmetries
such that a dominant can appropriate resources at will. To date the only solution is Boehm’s
proposal, namely that morality was favored because allied males were selected to use
coercive behavior first to eliminate tyrants, then subsequently to favor prosociality and
punish antisociality. Using information on self-domestication, a topic that Boehm did not
explore, I present several tests of Boehm’s thesis. All are supportive, while also modifying
Boehm’s ideas. I conclude that a major increase in evolved groupishness began with the
origin of Homo sapiens and the ability to execute tyrants. This process generated Homo
duplex, including the uniquely human tension between selfishness and duty seen in hunter-
gatherers and other societies.