Fig. 1.

Population structure and relatedness, reproduced from Hamilton (17), who discussed how limited dispersal induced by various population structures influences patterns of relatedness and thereby affects the evolution of social behavior. In the panmictic and viscous models, smaller dots indicate younger individuals, and arrows indicate parenthood. In the island and stepping-stone models, younger individuals are not shown because reproduction occurs within groups. Arrows indicate dispersal between groups. For the viscous, island, and stepping-stone models, locally interacting individuals are positively related under limited dispersal, and the local relatedness structure has been explored in the field of population genetics (13, 18–21). The viscous model with continuous space is the most challenging to analyze and remains the least explored, yet it is probably the most realistic model for plant populations. Most of the papers rediscovering kin selection use either the island model (using groups of size $>$1 and with interactions occurring within groups) or the stepping-stone model (using “groups” composed of a single individual, represented as the node of a lattice structure; since migration links nodes, the population becomes a network with interactions occurring between neighboring nodes). Reprinted with permission from ref. 17.