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The fourth branch

Is there a new class of micro-organisms?

By Philip Ball   May 2011

Robot companions may no longer be science fiction if the EU decides to fund a new project

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…

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