Data from the Human Gene Mutation Database were used to contrast the alternative hypotheses that microsatellites arise through insertions or through substitutions. The results showed that a high percentage of small insertions created novel microsatellite repeats through the duplication of the adjacent sequences. However substitutions were still the dominant source of new microsatellites since they are so much more common than insertions. Although insertions contributed a minority of new repeat loci, their relative importance increased rapidly with repeat motif sizes. Microsatellite techniques were then applied to examine genetic conflicts in the cellular slime mold, Dictyostelium discoideum. Microsatellite genotyping showed that genetically distinct clones generally formed multicellular fruiting structures together in the mixing experiments. More interestingly, some clones were found to preferentially become reproductive spores instead of non-reproductive altruistic stalk cells. These conflicts of genetic interest make D. discoideum a potential excellent model system for social evolution.