When this happens, the group must resort to punishment in order to maintain cooperation among members. And, this punishment is coordinated and conditional.
In the April 29, 2010 National Science Foundation's article 'Coordinated Punishment Leads to Increased Cooperation in Large Groups' states that 'The finding challenges previous cooperation/punishment models that argue punishment is uncoordinated and unconditional.'
Dr. Boyd and his team report their research's findings in the April 30, 2010 issue of the journal Science. The article's title is "Coordinated Punishment of Defectors Sustains Cooperation and Can Proliferate When Rare" (DOI: 10.1126/science.1183665).
The NSF article adds, ''¦ it turns out that most members of large groups cooperate. Why? Boyd and his colleagues suggest cooperation is maintained by punishment, which reduces the benefits to free riding. There are tribes, for example, that punish free-riders who do not participate in warfare by not allowing them to take a bride. Thus, there is the threat of losing societal benefits if a member does not cooperate, which leads to increased group cooperation.'
And, 'Previous models of cooperation assumed that punishment of free-riders was uncoordinated and unconditional. One problem with these models was that the costs associated with punishment were often higher than the gains of cooperation. Thus, the cost of one group member's punishing a free-rider would be substantial and would not overweigh the gains achieved through increased cooperation.'
Page three concludes.