The growth of European cities around the year 1000 was caused by

Renewed trade, larger population, better farming methods. The growth of trade led to the rise of the first large trading centers of the later Middle Ages. They were located on the important sea routes that connected western Europe with the Mediterranean Sea, Russia, and Scandinavia. Two of the earliest and most important trading centers were Venice and Flanders.

they wanted the u.s. to fight on the side of the central powers.

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.