Seeing the Big Picture on Microbe Distribution

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Science  18 Sep 2009:
Vol. 325, Issue 5947, pp. 1506-1507
DOI: 10.1126/science.1179690

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Statements about the distribution of organisms can be made at all levels of phylogenetic scope and taxonomic resolution. The distributions of organisms on Earth reflect the interplay of dispersive trends with opportunity, obstruction, and extinction over time. If dispersal dominates, taxa tend to be widely distributed, and we rationalize presences and absences with greater reference to ecology. Where dispersal is constrained, taxa are more endemic, and we seek explanations by reference to history. For microbes, the idea that “everything is everywhere, but the environment selects,” first mooted by Sprengel almost 200 years ago, still maintains support (15), but a recent review of molecular data suggested that it is simplistic or wrong (6). Two reports in this issue (7, 8) help to evaluate which concept best describes the distributions of marine microbes. In doing so, they raise broader issues about the nature of biological knowledge.