What did the caste system in india and the fuedil system in europe have in common?
a. division of society into hereditary social classes
b. encouragement of trade between countries
c. peasants could live anywhere except land that was part of lords estate
d. strong emphasis on acquisition of wealth

genetics is the study of how dna works, the methodologies defining the new recent technologies allow scientist to have a panoramic view of the entire dna landscape, especially how genomes interact with their environment, including off course, factors outside their organisms.

thus is very possible the existence of both scenarios, where populations of isolated individuals have different genetic traits, and share traits related to genetic mutation, due rats can easily travel overseas using human transport channels. so scientists could get a vast number of data, including human interaction, evolution of rodents, health development, spread of infections, development of new organisms, how genomes evolve in different environments and so on.