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New York Times:

But the brown rats of Europe became the true globe-trotters. As Western European countries colonized other parts of the world, they took the rodents with them.

The brown rats of New York and other Eastern American cities trace their ancestry to those in Western Europe. So do brown rats in South America, Africa, New Zealand, and isolated islands scattered across the Atlantic and Pacific.

Even today, the ports of New York City are visited by rats from around the world.