Through the millennia wave after wave of migrants – often in the form of invading armies — have descended upon the British Isles.The first people to arrive after the Ice Age were hunter-gatherers who followed their prey north from southern Europe about 12,000 years ago. The Celts came from central Europe about 3,000 years ago. Then came the Romans, followed by the Anglo-Saxons, Vikings and finally the Normans in 1066 AD.With each successive invasion, the previous people were either absorbed by the invaders, or retreated to the isolated corners of the Isles. Often called the “Celtic Fringe,” these regions have been studied as a window into the ancient history of the British Isles. Some scholars even propose that the present-day people of the fringe could be direct descendants of the earliest humans to arrive on the Isles after the Ice Age.But despite exhaustive research into the history and genetics of the Celtic Fringe, its prehistory remains mysterious, forcing scientists to think outside the box. In the September 30 issue of the Proceedings of the Royal Society B: Biological Sciences, biologist Jeremy Searle and his research team did just that, devising an unconventional method to study the prehistoric peopling of the British Isles.They could have examined the DNA of the Celts themselves. But that’s already been tried, so Searle and his colleagues turned their research underfoot.Earlier analysis found similar genetic patterns in populations of both common shrews and humans inhabiting the Celtic Fringe. Using those results as a benchmark, Searle and his team expanded the genetic analysis to the pygmy shrew as well as two species of voles.Searle reasoned that if these shrews and voles had similar immigration patterns to early humans, perhaps those patterns would show up in their DNA. Specifically, he believes that “this study can help us understand why humans in the British Isles form a Celtic Fringe.”Interestingly, Searle and his colleagues’ analysis revealed a division in DNA types for the shrews and voles similar to that separating the people of the Celtic Fringe and the rest of the British population. Further analysis revealed that the DNA types for the mammals living in the Celtic Fringe were quite old. So old, in fact, that Searle and his team propose that the arrival of these mammals traces all the way back to the post-Ice Age arrival of humans 12,000 years ago.If the mammals living in the Celtic Fringe date back 12,000 years, the people living there could as well.There is one problem with this hypothesis. The Celts themselves only arrived from mainland Europe 3,000 years ago, not 12,000 years ago. Conventional wisdom states that the Celtic Fringe only evolved after the Celts were pushed back following the invasion of the Romans and Anglo-Saxons.How does Searle explain this discrepancy? He and his team argue that the Celtic Fringe is not actually Celtic in origin. Rather, its presence predates the arrival of the Celts and their arrival only ‘reinforced’ a pre-existing division that was already there.In that case, it would have been the Celts themselves whose arrival pushed earlier inhabitants to the isolated corners of the British Isles. Subsequent migrations would have pushed the Celts into these same corners, which is why the language and culture of these regions are inherently Celtic. And that would also explain why the languages, culture, and history of the pre-Celtic people of Britain have mostly been lost to time.