Table 1.

Model parameters and values.

	parameter	default value (range)
m	number of groups	20 (5,50)
n	group size	10 (5,30)
a	baseline payoffs	10 (1,20)
γ	wealth elasticity	(−5,5)
b/c	benefit-to-cost ratio	1.25
d	global externality	d is set in model simulations so that $dp/nm=\hat{d}$, for p = 1; in the baseline $\hat{d}=2.5$
$p_{\mathrm{con}}$	probability of conflict	0.05 (0.05–0.25)
µ	mutation	0.01
α	strength of within-group (individual) selection	0.5 (0.5–1)