  In the study of the evolution of cooperation, resource limitations are
usually assumed just to provide a finite population size. Recently, however, it
has been pointed out that resource limitation may also generate dynamical
payoffs able to modify the original structure of the games. Here we study
analytically a phase transition from a homogeneous population of defectors when
resources are abundant to the survival of unconditional cooperators when
resources reduce below a threshold. To this end, we introduce a model of simple
agents, with no memory or ability of recognition, interacting in well-mixed
populations. The result might shed light on the role played by resource
constraints on the origin of multicellularity.
