“…Such 'mutualisms' -for the purpose of collective defence, or collaborative hunting -are widespread in nature (Bissonnette et al, 2015;Boinski & Garber, 2000;Boos, Kolbe, Kappeler, & Ellwart, 2011;Harcourt & Waal, 1992), and are an ancient and recurrent feature of human social life (Alvard, 2001;Wrangham, 1999). This process has led, in humans, to a psychology that forms and maintains groups (clubs, gangs, clans, sects, nations, and so on), and acts to promote their interests (sometimes at the expense of rival groups) (Balliet, Wu, & De Dreu, 2014).…”