Talk about following your gut. When humans first trekked out of Africa about 58,000 years ago, they carried with them stone tools, animal skins--and bacteria that cause ulcers and stomach cancer. These anatomically modern humans unwittingly had the guts to spread Helicobacter pylori into Eurasia, where they passed on the bacteria to their descendants, according to a report published online 7 February in Nature. "The evidence is really convincing," says microbiologist Mark Achtman of the Max-Planck Institute for Infection Biology in Berlin, principal investigator of an international team that traced the origins of the bacteria in modern humans.
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