A seed bank stores seeds of crop varieties in cold, dry conditions so that they remain alive for decades. The purpose is not nostalgia. Modern farming relies on a small number of high-yielding varieties, and a disease that defeats one of them can spread across a continent, since the fields are genetically almost identical. Breeders answering such an outbreak need old varieties that were never bred for yield but may carry resistance. The bank is insurance against a risk created by the efficiency of the system it serves.