A mobile wireless ad hoc network (MANET) consists of a number of devices that form a temporary network operating without support of a fixed infrastructure. The correct operation of such a network requires its users to cooperate on the level of packet forwarding. However, a distributed nature of MANET, lack of a single authority, and limited battery resources of participating devices may lead to a noncooperative behavior of network users, resulting in a degradation of the network throughput. Thus, a cooperation enforcement system specifying certain packet forwarding strategies is a necessity is such networks. In this work we investigate general properties of such a system. We introduce a Prisoner's Dilemma-based model of packet forwarding and next using an evolutionary game-theoretical approach we demonstrate that cooperation very likely to be developed on the basis of conditionally cooperative strategies similar to the TIT-FOR-TAT strategy.