Technical Abstract: The birth-and-death model of multigene family evolution has been extensively characterized in eukaryotes over the last decade. However, this mode of multigene family evolution has not been described for bacteria. By not considering the birth-and-death mode of gene family evolution, the extent of lateral transfer events may be artificially projected upwards. The purpose of this study was to investigate whether this holds true in a representative bacterial multigene family, the internalins. Our findings indicate that internalins evolve under a birth-and-death process. Lateral transfer was detected twice, but the estimated frequency would have been much higher had it not been analyzed within the context of birth-and-death evolutionary dynamics and a phenomenon that we term “gene duplicate-sorting”, which involves the unequal transmittal of gene duplicates during or subsequent to the speciation process. Within this framework, we suggest that the frequency of lateral transfer in bacterial multigene families may be artificially inflated and that its extent should be reinterpreted in the light of birth-and-death evolution.