frequent in regions of the world with low rates of gastric cancer, such as Australia and North America. A third vacA polymorphic site, the intermediate (i) region was more recently identified, with variants i1 and i2. Strains type i1 were associated with higher risk of gastric adenocarcinoma.38 OUT OF AFRICA Increasing evidence supports the hypothesis that H. pylori was already established in human stomachs at least 100,000 years ago, before the human migration out of Africa about 60,000 years ago.26 Fig. 1, from Covacci et al .,26 displays the ancient human migrations and the approximate time of each migration wave. It has been hypothesized that after migration out of Africa, humans reached Asia by a southern coastal route, through India and then into South East Asia and Australasia.39 That route extended along the region known as Sundaland (including the Malay peninsula, Sumatra, Java, and Borneo), that was part of the Asian mainland as a result of low sea levels during the last ice age.40 Also due to the low sea levels, Austra- lia, New Guinea, and Tasmania were connected in a continent called Sahul, separated from Sundaland by a few narrow deep- sea channels.41 The modern humans settled Europe about 30,000 to 40,000 years ago, probably entering via two routes: from Turkey along the Danube corridor into Eastern Europe, and along the Mediterranean coast. Finally, Homo sapiens and H. pylori crossed the Bering Strait together approximately 12,000 years ago and then continued their migration to the Americas. During the last decade, genotyping of H. pylori strains ob- tained from multiple human populations around the world has demonstrated that the genetic diversity of this bacterium reflects human migrations and subsequent geographic and ethnic sepa- ration between human groups. Analyses of genetic diversity of H. pylori are more frequently carried out by comparing sequences Table 1. Genetic Ancestral Prototype Populations of Helicobacter py- lori6,41,43,46,48 H. pylori population Geographic distribution hpEurope hpAfrica1 hspWAfrica hspSAfrica hpAfrica2 hpNEAfrica hpEastAsia hspEAsia hspMaori hspAmerind hpAsia2 hpSahul Europe, Middle East, India, and Iran Western Africa South Africa South Africa Ethiopia, Somalia, Sudan, northern Nigeria East Asians Taiwan Aboriginals, Melanesians, Polynesians Native Americans Northern India, Bangladesh, Thailand, Malaysia Australia Aboriginals and Papua New Guineans Correa P, et al: Evolutionary History of the Helicobacter pylori Genome 23 of housekeeping or virulence associated genes. Some authors have suggested that genotyping of H. pylori may be superior to human genetic markers to distinguish geographically related populations.42 Analysis of multilocus sequence typing (MLST) of housekeeping genes has shown to be a robust and consistent test to study ancestry and evolution of H. pylori populations. Based MLST of seven housekeeping genes (atpA, efp, mutY, ppa, trpC, ureI, yphC) and one virulence-associated gene (vacA) of 370 strains isolated from 27 human populations, Falush et al.43 identified four main clusters of H. pylori populations with distinct geographical distribution identified as: 1) hpEurope, 2) hpAfrica1, 3) hpAfrica2, and 4) hpEastAsia. Further analysis split hpEastAsia into hspAmerind, hspEAsia and hspMaori sub- populations. hpAfrica1 was subdivided into hspWAfrica and hspSAfrica.43 More recent studies identified other main clusters: hpNEAfrica, hpAsia2, and hpSahul (Table 1).6,41 EVOLUTION OF ASIAN H. pylori STRAINS It could be speculated that the H. pylori genome from the ancient Asian strains were less carcinogenic than the present more carcinogenic Asian and European strains. This change may be reflected in the elevated gastric cancer rates observed in Korea and Japan, where the H. pylori strains possess CagA with EPIYA-D motifs, linked to higher phosphorylation and higher cancer risk. Although the genotype of the ancient Asian strains is not known, it is generally assumed that that their viru- lence and carcinogenic potential was very low.44 Censini et al.22 linked the hypothetical emergence of virulent variants from less virulent variants to the acquisition into the H. pylori genome of the cag PAI. Present day evidence suggests that the secular evolution of the ancient Asian strains differed in Asia and the Americas. In both continents the cag PAI was inserted into the H. pylori genome, but the CagA protein in East Asian strains has an EPIYA-D motif and the Western version has instead one or more EPIYA-C motifs. Recent evidence supports a possible evo- lutionary pathway for the EPIYA-D segment by sequence rear- rangement within the cagA gene.45 This work, by Furuta et al.,45 supports that the left half of the EPIYA-D segment characteristic of East Asian CagA was derived from Western-type EPIYA, and suggests that Amerind-type EPIYA could have been the inter- mediate, through rearrangements of specific sequences within the gene. The value of H. pylori genome as a marker of human migra- tions has been well illustrated in studies carried out in Ladakh, an isolated location in the trans-Himalayan region of Northern India.42 Two separate groups with independent social and re- ligious characteristics inhabit Ladakh: Buddhists, primarily of Mongoloid Tibetan descent, and Muslims who migrated from Pakistan in the 14th century. The classical human genetic mark- ers were insufficient to distinguish the two Ladakh communities. But H. pylori sequence analyses clearly showed the differences