In 2015 Jeremy Searle, professor of ecology and evolutionary biology, and two co-authors posited, based on mouse mitochondrial DNA, that the first humans to visit the Azores came from Northern Europe, not Portugal. Their study, published in the Journal of Evolutionary Biology, has taken on new relevance in light of a new, international study published in the Proceedings of the National Academy of Sciences (PNAS), which looked at sedimentary layers in Azores lakes and historical climate patterns and came to the same conclusion Searle’s group did: Norse explorers discovered parts of the Azores between 700 and 850 A.D.
“This is a completely different set of data, but their findings confirm what we hypothesized in 2015,” Searle said. “Having this variety of available evidence: the sedimentary record, historical climate data, our mice – our living artifacts – these are all tools for archaeologists and historians to use in piecing together the past.”
For 20 years scientists have been studying the mitochondrial DNA of house mice to learn more about human visitation and settlement in far-flung places; because house mice live alongside humans, the presence of one almost guarantees the presence of the other. Studying the genetics of living mice can give clues about their ancestors because mitochondrial DNA – the portion of the genome that is exclusively passed by females – remains virtually unchanged through generations particularly in a closed, island environment, Searle said. While later-arriving males may outcompete and genetically displace existing males, the DNA of first-arriving females seems to remain permanently dominant, he said.
“We’ve found that these mitochondrial DNA sequences seem to be a really good marker for first colonization of islands,” he said.
Additionally, house mouse mitochondrial DNA is genetically distinctive between geographic regions: The DNA of mice from southwest Europe is different from the mice of Britain and different from the mice of Scandinavia. Searle’s team found that Azorean mice had mitochondrial DNA suggesting an early colonization from the far north of Europe, just as expected if the Norse transported them.
The new study in PNAS explored the sedimentary layers of Azores lakes. That research found evidence of human settlement between 700-850 A.D.: They found compounds associated with livestock feces, charcoal remains associated with controlled burning of wood by humans, and pollen signatures that would only occur with some level of intentional deforestation, Searle said.
“Our suggestion was that the Norwegian Vikings might have visited the Azores – you only need to have a very short visitation for mice to get on the island – but we didn’t say anything about them having settled there,” Searle said. “This new research indicates that there was substantial human occupation and settlement of the Azores during that period, and the dates match well with the time when the Vikings were moving around the North Atlantic.”
The 2015 paper that first proposed Viking discovery of the Azores is “Of mice and the ‘Age of Discovery’: the complex history of colonization of the Azorean archipelago by the house mouse (Mus musculus) as revealed by mitochondrial DNA variation.” First author is Sofia Gabriel, then a Ph.D. student with Searle, now a postdoctoral fellow at the University of Lisbon.
Krisy Gashler is a writer for the College of Agriculture and Life Sciences.
Header image: House mouse (Mus musculus). Photo by Sofia Gabriel, postdoctoral fellow at the University of Lisbon
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