H. pylori, which infects the mucus lining of the stomach and duodenum, is the o­nly known microorganism able to flourish in the stomach's highly acidic environment.

The finding, published o­nline Wednesday in the journal Nature, could provide insights into both medicine and anthropology, the scientists said, since it improves understanding about ulcers and also offers a new way to study early human migration and diversification.

"Humans and this ulcer-causing bacterium have been intimately linked for the last 60,000 years," researcher Dr. Francois Balloux, of the University of Cambridge in the United Kingdom, said in a prepared statement.

The researchers compared the DNA sequence patterns of humans and H. pylori and discovered that genetic variations developed as humans dispersed from Eastern Africa over thousands of years.

"The research not o­nly shows the likelihood that for tens of thousands of years our ancestors have been suffering the effects of this bacteria, but it also opens up new possibilities for understanding early human migration. For example, we could use our understanding of the bacteria's spread to gauge poorly understood human population shifts in Europe, Africa and Asia," Balloux said.

Until the 1990s, it was widely believed that stress and spicy foods caused peptic ulcers and gastritis. Now that H. pylori is recognized as a major cause, these conditions are now treated with antibiotics that are effective against the bacteria.