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PNAS u January 26, 2010 u vol. 107 u no. 4 u 1255–1256 www.pnas.org/cgi/doi/10.1073/iti0410107 A genomic analysis of the undersea Lost City Hydrothermal Field (LCHF) in the Atlantic Ocean reveals how microbial populations can rapidly grow and fade over a millennium. The research may also provide a time series showing how environmental change and natural selection determine the dominance of one species over others. William Brazelton et al. (pp. 1612–1617) sequenced ribosomal RNA genes from bacteria and archaea collected from the LCHF, a unique system of hydrothermal vents near the Mid-Atlantic Ridge that is home to dense communities of microbes. The authors found that many microbial species shifted from rare to dominant over the past 1,200 years as environmental conditions such as ocean temperature and pH changed. The species that became dominant came from an extremely diverse pool of rare organisms that were able to exploit the environmental conditions and increase their population at the expense of other species. The cycle, similar to evolutionary processes that have occurred countless times as life progressed on Earth, is continuing as the chimneys grow and develop, according to the authors. — P.D.