Eight thousands years ago, people brought snails from Spain to Ireland, suggests a new study, which used DNA analysis to identify a snail species that lives today only in Ireland and the Pyrenees mountains between France and Spain.
In both places, the snails have large, white-lipped shells. And, according to the new work, the two groups also share genetic markers that are extremely rare elsewhere in Europe.
Along with other evidence, the findings offer a new window into ancient human migrations.
"It's interesting to use snail genetics to find out how snails colonize, and it also maybe gives us a little insight into what humans were doing, too," said Angus Davison, an evolutionary geneticist at the University of Nottingham in the United Kingdom.
"One really neat thing about this study is that, if we accept that humans transported snails, it really gives us a unique insight into an individual journey 8,000 years ago, and it gives us evidence of that from a source you might not imagine."
For more than 150 years, biologists have been puzzling over an Irish mystery: A number of wildlife species that live in Ireland are absent from the rest of Britain but are found in Iberia, the peninsula that includes modern-day Spain, Portugal and parts of France.
Research into this so-called "Irish question" has failed to produce a single theory that explains how and when various species covered hundreds of miles from one place to the other.
To see if they could add any new understanding to the Irish question, Davison and colleague Adele Grindon focused on a distinctive-looking snail that had the same one-inch long shells in both locations. According to fossil evidence, the snails first showed up in Ireland about 8,000 years ago. The mollusks had lived in southern Europe for tens of thousands of years before that.
First, the researchers enlisted volunteers to help collect nearly 900 snails from both parts of its range. Then, they extracted mitochondrial DNA, which is passed directly from mother to offspring, and they looked at specific areas of the genome that are known to vary from snail species to snail species.