“…In respect of the evening meal, they were also asked to say how many people were present (2, 3, 4 or 5+, including themselves) and, on a simple binary choice, whether or not any of the following had occurred during the meal: laughter, reminiscences, jokes, singing, dancing, party games, drinking alcohol or eating chocolate. Laughter, singing, dancing and storytellling are all known to trigger the endorphin system Pearce et al 2015;Tarr et al 2016;Dunbar et al 2016), the main pharmacological factor underpinning social bonding in primates and humans (Curley and Keverne 2005;Depue and Morrone-Strupinsky 2005;Machin and Dunbar 2011). Alcohol is also a major trigger of the endorphin system (Naber et al 1981;Van Ree 1996;Hertz 1997;Gianoulakis 2004) -so much so that an endorphin antagonist such as naltrexone is now the treatment of choice for alcohol addiction (O'Brien et al 1996;Saland et al 2008).…”