Such a natural laboratory is not so critical for cultural evolution - since we can easily see that going on in real time. However, fortunately, we do have some natural laboratories, and they do provide some interesting data.
Memes get isolated on islands in much the same way as genes do. Perhaps the greatest natural experiments in island cultural isolation took place in Australia and Japan. Both were colonised by humans many tens of thousands of years ago. Australia's culture developed slowly, and has subsequently been rather messed up by European settlers - but in Japan much of the original culture has survived and thrived.
I figure this makes Japan the Galapagos of memetics. A map illustrates the extent of its isolation from the mainland of China and Korea. Far enough to reduce meme flow to a trickle.
Japanese culture is rich, old and contains many interesting and well-known features. Many of these are related to the culture of nearby mainland China - but often there are interesting differences. Japan has its own martial arts, sports, religions, games, cuisine, architecture, traditions and ceremonies.
In the organic realm, islands are mostly evolutionary dead ends. They are eventually invaded by predators and more effective creatures from the mainland, who wipe them out. However, they also sometimes act as evolutionary incubators and sources of innovation and new species. In Japan I think we can see the cultural equivalent of that. Japan is one of the rare islands where interesting cultural evolutionary innovation has happened. In this case, the results are strong and vibrant enough to persist and go on to influence what happens on the mainland.