We study the stability of voluntary cooperation in response to varying group growth rates. Using a laboratory public-good game, we construct a situation where increasing group size yields potential efficiency gains, but only with sustained cooperation. We then study the effect of exogenously...

Prior research demonstrates a willingness to incur costs to punish norm violators. But, how strong are the motives underlying such acts? Will people rely on "excuses" to avoid acting on costly punishment intentions, as with other costly pro-social acts? In a laboratory experiment, we find that...