Snails found both in Ireland and the Pyrenees Mountains (located in southern France and northern Spain) may hold clues about the migration of humans in these areas long ago.
Banded wood snails in the two regions are similar to one another - studies of their genetic makeup show that they are nearly identical. Not only do they share identical shell markings, but also have matching mitochondrial DNA.
No snail like it is seen anywhere between the two locations, which likely rules out a natural migration of the snail without human assistance. The genetic markers point to the species being transported from the French mainland to Ireland 8,000 years ago, during a migration of people as the last ice age ended.
At that time, rising sea levels triggered large land- and mudslides, and Britain, once connected to the European continent and Ireland, became an island.
"There is a very clear pattern, which is difficult to explain except by involving humans. If the snails naturally colonized Ireland, you would expect to find some of the same genetic type in other areas of Europe, especially Britain. We just don't find them," Angus Davison of the University of Nottingham in the United Kingdom, said.
Davison discovered that the 8,000-year-old marker found in the DNA of banded wood snails also matches up with a human marker in the genetic code of people in those two areas. This suggests a migration of humans from southern France to Ireland at that time.
There is evidence that the ancient people of the Pyrennes region in what is now France were eating banded wood snails, and the creatures could have either hitched a ride on the underside of boats or been carried along on purpose for food.
The Garone River, which winds its way through the Pyrennes, was an ancient highway for the people of the region 80 centuries ago. The river runs for 375 miles, and could have been the route by which the snail was delivered to the island of Ireland.
"The highways of the past were rivers and the ocean - as the river that flanks the Pyrenees was an ancient trade route to the Atlantic. What we're actually seeing might be the long lasting legacy of snails that hitched a ride as humans travelled from the South of France to Ireland 8,000 years ago," Davison said.
This new finding may help answer a puzzle which has become known as "the Irish question." Many species of plants and animals appear in both Ireland and mainland Europe, but not in Britain. These human migrations may explain the mystery.
The study of the snail and its relation to human migration was published on PLOS ONE, the open-source online journal operated by the Public Library of Science.