Out on a limb

摘要

The e-mail arrived two weeks after Jonathan Eisen's paper was published. Tongue-in-cheek, it read: Welcome to the Fourth Domain' club." Eisen, an evolutionary biologist at the University of California, Davis, chuckled. His paper', which came out in March, hinted at bizarre new forms of microscopic life in the ocean. The e-mail was from Didier Raoult, a biologist at the University of the Mediterranean in Marseilles, France, who for years has argued that the colossal viruses he has identified belong to a unique, hitherto unknown, branch of life: the fourth domain. Raoult believes that this domain branched off from the very base of life's evolutionary tree - a declaration that has been met with strong scepticism. Researchers disagree with the way he interprets sequence data. The debate highlights how hard it is to decipher the original relationships between microorganisms that have swapped, tinkered with and generally scrambled their DNA over billions of years.