The coat pattern of calico cats does not define any breed, but occurs incidentally in cats that express a range of color patterns; accordingly the effect has no definitive historical background. However, the existence of patches in calico cats was traced to a certain degree by Neil Todd in a study determining the migration of domesticated cats along trade routes in Europe and Northern Africa. The proportion of cats having the orange mutant gene found in calicoes was traced to the port cities along the Mediterranean in Greece, France, Spain and Italy, originating from Egypt.