Evolution of cooperation with an initial hare-hunting strategy and a reward for solitary stag hunting.

(a) Evolution of the mean percentage of stags hunted successfully (i.e. cooperatively) with respect to the total number of prey hunted in a robotic simulation. (b) Mean number of prey hunted during the last generation of evolution for each independent run. The bottom green bar represents the number of hares hunted, the middle pink bar the number of stags hunted cooperatively and the top grey bar the number of stags hunted alone. The standard deviation for each quantity is shown by black lines. The population for each of the 30 independent runs was previously evolved in an environment with only hares. Rewards were 50 for a hare, 50 for a stag hunted alone, and 500 for a stag hunted cooperatively as presented in Table 3. The number of prey (18) was kept constant throughout the simulation by replacing killed prey by a prey of the same type.