In his 2019 book Blueprint: The Evolutionary Origins of a Good Society, Yale sociologist and physician Nicholas Christakis describes research led by evolutionary biologist Jessica Flack, who ran studies with 84 macaques at the Yerkes National Primate Research Center. Flack’s team identified the group leaders in this monkey community, removed the highest-ranking members, and observed the resulting interactions. Chaos ensued. When high-ranking monkeys were “knocked out” (as the scientists called it), conflict and aggression soared. After the leaders were removed, the group had fewer grooming interactions and played less frequently. Social ties disintegrated. “This suggests that stable leadership promotes peaceful interactions not only between leaders and followers,” Christakis writes, “but also between followers and other followers.”
When the leaders were in place, they intervened between status-seekers and regulated social connections. Lower-ranking monkeys knew that if conflict arose, the higher-ranking monkeys would step in. The presence of leaders allowed lower-ranking monkeys to interact with one another without fear of attack. When the leaders were removed, the macaques began jockeying for power, which resulted in mayhem and violence.
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