Equilibria for a population of DISC players under ST and JG. (a) Cooperativeness (ψ) and (b) ingroup bias (ρ). We vary the assignment rule (ST or JG), the number of groups (M = 2 or 10), and the probability of ingroup interaction (θ). The lines represent theoretical results shown in Table 3. The symbols represent numerical results.
Nakamura and Masuda BMC Evolutionary Biology 2012 12:213 doi:10.1186/1471-2148-12-213