Short answers, pulled from the story.
The name Norway rat was popularized in 1769 by English naturalist John Berkenhout who believed the species migrated to England on ships from Norway in 1728. The species actually originated in northern China and neighboring areas and spread to Europe during the Middle Ages.
The brown rat species likely originated in northern China and neighboring areas before spreading to Europe and the rest of the world during the Middle Ages. It traveled from Persia to England and then to other countries visited by English ships where it displaced the black rat.
The brown rat has acute hearing sensitive to ultrasound and possesses a highly developed olfactory sense while its vision is poor but allows it to see ultraviolet light. It is a good swimmer that can climb slim round metal poles and digs extensive burrow systems for shelter and food storage.
The brown rat can breed throughout the year with a gestation period of 21 days and litters numbering up to 14. Under ideal conditions the population can grow from 2 to 15,000 in a year due to females reaching sexual maturity in about five weeks.
Selective breeding has produced the fancy rat and laboratory rat as the domesticated subspecies Rattus norvegicus domestica with variations in coat patterns and body size. Studies of wild rats in New York City show that urban populations evolve distinct genomic profiles over time due to barriers like roadways and low garbage districts.