Equilibria and the stability conditions for a population of DISC players under MX. (a) Cooperativeness (ψ) and (b) ingroup bias (ρ). In (a) and (b), we set (M,θ) = (2,0.6),(∞,0.6), (2,0.2), and(∞,0.2). (c)–(f) Stability conditions. The homogeneous population of DISC players is stable in the shaded parameter regions. We set (c)(M,θ) = (2,0.6), (d)(M,θ) = (∞,0.6), (e)(M,θ)=(2,0.2), and (f)(M,θ) = (∞,0.2).