In what century did the Fall of the Roman Empire take place - 476 CE?

Since much of the west had already fallen by the middle of the 5th century CE, when a writer speaks of the fall of the empire, he or she generally refers to the fall of the city of Rome. Although historians generally agree on the year of the fall, 476 CE, they often disagree on its causes.

the american rail road was the most influential and useful transportation system developed in the 1800's with steam locomotives and in the very late 1800's and early 1900's diesel electric locomotives being used to transport goods and people around the newly expanded united states!

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.