Is there a new class of micro-organisms?by Philip Ball / April 20, 2011 / Leave a comment
Published in May 2011 issue of Prospect Magazine
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The 20th-century biologist and atheist JBS Haldane once offered the dry observation that if God existed, he had an inordinate fondness for beetles. But God surely favours single-celled organisms more: beetles and humans share the same neighbourhood (“animals”) on the tree of life, while single-celled life forms have two of the three fundamental branches—bacteria and archaea—all to themselves. Bacteria and archaea are so alike that the latter were awarded their own branch only in the 1970s. Archaea have a different biochemistry from bacteria—their metabolism usually produces methane—and they are found everywhere, including the human gut.
Now, a team at the University of California, working with genomics pioneer Craig Venter, claims to have found hints of a fourth major branch in the tree, again populated only by single-celled organisms. These branches, called domains, are the most basic divisions in the Linnaean system of biological classification. We share our domain, the eukaryotes (distinguished by the way cells are structured), with plants, fungi and yet more monocellular species.