In this paper, we consider medium access control of local area networks (LANs) under limited-information conditions as befits a distributed system. Rather than assuming "by rule" conformance to a protocol designed to regulate packet-flow rates (as in, e.g., CSMA windowing), we begin with a non-cooperative game framework and build a dynamic altruism term into the net utility. Our objective is to define a utility model that captures more closely the expected behavior of users, which according to recent results from behavioral and experimental economics should include a conditionally altruistic dimension. The effects of our proposed dynamic altruism are analyzed at Nash equilibrium in the quasi-stationary (fictitious play) regime. We consider either power or throughput based costs, and the cases of identical or heterogeneous (independent) users/players.