According to several articles I have read, the Italian gene pool has remained pretty stable for around the last four thousand years. This means that modern-day Italians are the direct genetic descendants of the ancient peoples of Italy who have been there since Roman times and before, since invading barbarian tribes (Ostrogoths, Lombards, etc) were too few in number to make a significant contribution to the gene pool.

How is it then that the people who called themselves Romans suddenly decided to start calling themselves Italians, Venetians, Florentines, and seemingly lost many cultural ties to their genetic ancestors? Why is it that the Greeks, for example, have managed to maintain their ethnic identity and still refer to themselves by the same name their ancestors used 2500 years before them, still speaking roughly the same language, while the Romans have completely lost it?