Figure 2
From: Which risk scenarios can drive the emergence of costly cooperation?
Average contributions in an evolutionary model.
Full lines show the Nash equilibrium calculated using Eq. (4). Single points represent the average contribution from ≈2000 realizations (a) for the Piecewise linear curve and (b) for the Fermi function with 
. These simulations confirm that the equilibria calculated here can also be obtained as the average of an evolutionary process. For the Fermi curve, the curve must become steeper with increasing d to stabilize the equilibrium, as discussed in the main text (N = 100, G = 1000, μ = 0.01, σ = 0.01).
