text: The function of msDNA remains unknown even though many copies are present within cells. Knockout mutations that do not express msDNA are viable, so the production of msDNA is not essential to life under laboratory conditions. Over-expression of msDNA is mutagenic, apparently as a result of titrating out repair proteins by the mismatched base pairs that are typical of their structure. It has been suggested that msDNA may have some role in pathogenicity or the adaptation to stressful conditions. Sequence comparison of msDNAs from Myxococcus xanthus, Stigmatella aurantiaca, and many other bacteria reveal conserved and hypervariable domains reminiscent of conserved and hypervariable sequences found in allorecognition molecules. The major msDNAs of M. xanthus and S. aurantiaca, for instance, share 94% sequence homology except within a 19 base-pair domain that shares sequence homology of only 42%. The presence of such domains is significant because myxobacteria exhibit complex cooperative social behaviors including swarming and formation of fruiting bodies, while E. coli and other pathogenic bacteria form biofilms that exhibit enhanced antibiotic and detergent resistance. The sustainability of social assemblies that require significant individual investment of energy is generally dependent on the evolution of allorecognition mechanisms that enable groups to distinguish self versus non-self.