Stomach bug gives clues to Pacific migrations
EU-funded researchers have analysed the genetic sequence of bacteria found in the stomachs of native people in the Pacific in order to shed new light on how and when humans colonised this vast, diverse region. Their findings, published in the journal Science, confirm previous studies from the fields of archaeology, linguistics and human genetics. EU support for the study came from the PathoGenoMics ('Trans-European cooperation and coordination of genome sequencing and functional genomics of human-pathogenic microorganisms') ERA-NET project, which is financed under the 'Coordination of research activities' budget line of the Sixth Framework Programme (FP6). When our ancestors left Africa some 60,000 years ago, a stowaway tagged along in their stomachs: Helicobacter pylori. Today, half of the world's population is infected with H. pylori bacteria, and the bug has been linked to stomach ulcers and an increased risk of cancer. This latest study builds on previous work demonstrating that different continents are home to different strains of the bug. As the human populations spread out across the world, split up and diverged genetically, so did the populations of H. pylori they carried with them. These patterns are still visible today: people in Europe are infected by a strain called hpEurope, while Asians suffer from the strains hpAsia2 and hpEastAsia, for example. 'About 10 years ago, we discovered that the [strain of] bacteria in Europe is different from that in China,' commented Mark Achtman of the Max Planck Institute for Infection Biology in Germany. 'In 2003, we were able to show that a strain of the bacteria came to North America with the slaves.' In this latest study, the scientists analysed over 200 samples of H. pylori taken from native Pacific populations, including aboriginals in Taiwan and Australia, highlanders in New Guinea and Melanesians and Polynesians in New Caledonia. Some samples were donated from doctors and hospitals, while in some areas doctors invited representatives of aboriginal populations to participate in the study. The results reveal two strains of the bacteria that appear to have been evolving separately for thousands of years. Inhabitants of New Guinea and Australia were found to be infected with a strain of the bacteria called hpSahul, which split from Asian populations between 31,000 and 37,000 years ago. At that time, low sea levels meant that Australia, New Guinea and Tasmania formed a single landmass called Sahul, and just a few deep sea channels separated Sahul from what is now the Indonesian archipelago. The second strain identified in the samples was hspMaori, which is related to the hpEastAsia strain and appears to have left Taiwan some 5,000 years ago before spreading out to the Philippines and into Polynesia and New Zealand. 'Our results lend support for two distinct waves of migrations into the Pacific,' the scientists write. 'First, early migrations to New Guinea and Australia accompanied by hpSahul and second, a much later dispersal of hspMaori from Taiwan through the Pacific by the Malayo-Polynesian-speaking Lapita culture.' The researchers were surprised to find that not one sample contained both newly discovered strains of the bacteria. This could be because the early populations had very little contact with one another, or because one strain is stronger and always takes over when the two meet. 'Alternatively, hpSahul and hspMaori may still coexist in unsampled islands of East Asia, Melanesia and coastal New Guinea, where their identification might help to unravel the details of human history in those areas,' the researchers note. Interestingly, in the same issue of Science, a detailed investigation by New Zealand scientists of the Austronesian language family paints a similar picture to that painted by the genetic analysis of H. pylori. In an accompanying comment article, Colin Renfrew of the UK's University of Cambridge wrote: 'The convergence between the approaches suggests that a synthesis between linguistic and genetic interpretations of human history may soon be possible on a worldwide basis.'