 Consider some of the species concepts developed by microbiologists. One microbial species concept, the Recombination Species Concept, asserts that species are groups of microbes whose genomes can recombine (Dykuizen and Green 1991). The motivation behind this species concept is that though microbes generally do not reproduce sexually, they form gene pools of organisms connected by recombination. Another microbial species concept is Cohan’s (2001, 467) ecological concept in which a “species in the bacterial world may be understood as an evolutionary lineage bound by ecotype-periodic selection.” According to Nesbo et al. (2006) and others, these two microbial species concepts sometimes sort the same organisms into different species. A third microbial species concept, the Phylo-Phenetic Species Concept (Rossello-Mora and Amann 2001), is different than the first two. While the Recombination and Ecological Concepts are based on biological theory about the nature of microbial species, the Phylo-Phenetic Species Concept is designed to obtain stable classifications of species that can be used in medical and microbial research.