A Survey of Replicator Equations

What are the units of natural selection? This question has aroused considerable debate in theoretical biology. Suggestions range from pieces of polynucleotides, genes, or gene complexes to individuals, groups, or species. It could be, however, that different answers are correct in different contexts, depending on the scale on which selection acts most decisively. This is somewhat analogous to physics, where the dominant force may be gravitational, electromagnetic, or strong or weak interparticle attractions, depending on the problem.