Domestic cats spread from the Middle East and Egypt to other parts of the world in three phases.

Early archaeological sites where the remains of cats and humans have been found together.

Phase 1: 6000 B.C.-200 B.C. During this period, cats made the transition from semi-wild residents of human settlements to fully domesticated members of the household. Some cats made their way to Rome on trading ships.

Phase 2: 200 B.C.-1400 A.D. Cats spread through Europe and Asia with the expansion of the Roman Empire, the silk trade, and Christian and Buddhist missionary movements. By the end of this period, domestic cats could be found from Ireland to Japan.

Phase 3: 1400 A.D.-Present. Cats travelled on ships as mousers and began to cross the seas in the fifteenth and sixteenth centuries. Colonization by European countries brought cats to other continents. By about 1850, cats could be found almost anywhere there were people.

Scientists can use the physical traits of cats to trace their spread around the world. For example, cats with extra toes (polydactyly) have left a distinctive "trail" in eastern North America. Cats with this rare genetic trait are strangely common in Boston and in two cities in Nova Scotia. Scientists believe that polydactylous cats were first brought to Boston in the 1600s and that some of their descendants were then carried to Halifax and Yarmouth along well-established shipping routes.