The evolution of extreme cooperation via shared dysphoric experiences

Abstract

Willingness to lay down one's life for a group of non-kin, well documented historically and ethnographically, represents an evolutionary puzzle. Building on research in social psychology, we develop a mathematical model showing how conditioning cooperation on previous shared experience can allow individually costly pro-group behavior to evolve. The model generates a series of predictions that we then test empirically in a range of special sample populations (including military veterans, college fraternity/sorority members, football fans, martial arts practitioners, and twins). Our empirical results show that sharing painful experiences produces "identity fusion" - a visceral sense of oneness - which in turn can motivate self-sacrifice, including willingness to fight and die for the group. Practically, our account of how shared dysphoric experiences produce identity fusion helps us better understand such pressing social issues as suicide terrorism, holy wars, sectarian violence, gang-related violence, and other forms of intergroup conflict.

Figure 1. Shared dysphoric experiences.

(a) Bruises and welts from Brazilian Jiu Jitsu belt whipping gauntlets (Photos: Guillaume Huni). (b) Memorial in Misrata to the thousands of revolutionaries in Libya who laid down their lives in the 2011 uprising (Photo: Harvey Whitehouse).

Figure 2. Effects of the benefit b, cost c, group size n, and the weight of previous experience h on the average individual efforts in euphoric groups and dysphoric groups .

(a,b) “us vs. nature” contests with the frequency of euphoric groups π = 0.5. In these games, the value of π does not affect the outcomes. (c,d) “us vs. them” contests with π = 0.2. (e,f) “us vs. them” contests with π = 0.8. The height of the bars is also reflected in their color using the gray colormap (low values in black and high values in white; specific to each individual panel). Notice the difference in the y-scale between subgraphs.