Horizontal gene transfer between organisms allows us to understand genealogical relationships in prokaryote evolution. 'Over long periods of time gene transfer makes organisms existing in the same environment more similar to one another. This is most clearly seen in the case of organisms that live in environments that are otherwise inhabited by distant relatives only.' Thus, Gogarten concluded, 'the boundaries between prokaryotic species are fuzzy. Therefore the principles of population genetics need to be broadened so that they can be applied to higher taxonomic categories.'
See also: Genomes and the Tree of Life Tree of Life Horizontal Gene Transfer in Prokayotes