How Rats Accidentally Preserved Clues to Human History

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Rats have lived alongside people for thousands of years, and their habit of collecting useful objects has left behind an unusual record of human life. Researchers have found buttons, pins, thread, scraps of clothing, fishing gear, food remains and other everyday items in rat nests. Because some nests stayed hidden and dry for long periods, objects that might normally have disappeared could survive for researchers to study. In historic buildings, rat nests can reveal what people made, used or discarded nearby. The objects can even provide clues about local work and the materials available to a household. Rats generally stay fairly close to their nests, so their collections can give researchers a surprisingly local snapshot of human activity. Rats can also help scientists study much older history. Genetic evidence from rat remains has been used to trace movements of rat populations that traveled alongside people across islands and continents. Since rats depended heavily on human food and transport, their remains can provide clues about connections between settlements and the movement of people. Pack rats provide another kind of historical record. Their large middens can contain plants, pollen, food remains, woven materials and other debris. In dry environments, rat urine can harden and help bind material together, allowing delicate traces to survive. Researchers have used these remains to reconstruct past diets and environments, including evidence from thousands of years ago. The result is an unusual archaeological resource. Rats were not intentionally preserving history, but their nesting and hoarding habits sometimes created accidental time capsules that scientists can use to investigate the past.