Retriever sent the BBC link on the ancient interconnectedness of fairy tales, and both James and Maggie's commented on it. A woman at church supper had run across the article (she used to be a professional storyteller), and later my son reported that my 8 y/o granddaughter had noticed that "Raiders of the Lost Ark" seemed to be a cross between "Star Wars" and "Lord of The Rings." Thus, it looks like I am obligated to weigh in on the subject in some way. Admittedly, the first three elements surrounding me may be related to each other.
I was initially very suspicious, and that may have influenced all subsequent reading. But I thought I'd have a go at the original study, and I was both confused and mildly encouraged. Their intent was not merely to see if they could find similar stories in diffuse Indo-European cultures, but whether they followed a pattern based on language more than geography, as would be considerably more likely with folktales. That is, they are not merely trying to determine whether a story about ravens giving advice occur in many lands, but if there is a pattern of particular raven-stories being more common in one linguistic line than another. I am also grateful that the researchers were properly tentative, in contrast to the (usual) journalists' blithe overconfidence of "Oh yeah, totally there. Traced it back to the Bronze Age."
Strong points: I think they have actually discovered some signal amidst the noise. There are a few stories that seem more common here than there, and strongly enough that the discovery of a lot of neutral story-data would not wash it out. It will be very interesting research to see over the next few decades whether stories in Sino-Tibetan, Altaic, or Amerindian languages show persistence over linguistic rather than geographic space, especially if the stories are not that similar to those in this study. Frankly that is the only evidence that would really convince me going forward. We have to see this in other language groups, not just our own heavily-researched one.
Problems: It is really hard to extract signal from noise in this sort of thing. Look at Figure 4 in the original study and look at the names of tales.
A lot of those stories sound like cultural universals that would just naturally pop up no matter where you lived. "The Faithless Wife," "The Lazy Boy." I'm thinking those aren't simply Indo-European concerns. Even something stranger sounding like "The Animal Bride," is known worldwide. There is a fairly common Korean story about a female bear who went into a cave and ate nothing but garlic for a long time in order to attract a human husband. (Hey, it could work.) There are animal brides and grooms in Amerindian stories. "The Monk and the Bird" sounds culture-bound at first, but when one steps back, that's likely to be something that shows up over and over again. Yet there are stranger stories that one would think could possibly show up anywhere, but wouldn't automatically show up everywhere: "The White Serpent's Flesh," or "Three Hairs."
Similarly, it is hard to know whether stray elements in a story are the real ancient connection, preserved like a fly in amber of thousands of years, or are random drop-ins, differing from valley to valley and signifying nothing. The hero drinks from a very fine cup - a good storytelling detail, but is it somehow important at a mythic level, a feature that captivated the minds of hearers over generations that kept one story alive while another vanished? Or is it an accident that happened to be preserved in the version we are familiar with.
Stories change, and they change quickly. If you pick up a book of folk tales that records versions before 1900, you will find them quite alarming in their strangeness. Here is one from the Brothers Grimm, and thus only a few hundred years old, not 10% of the time-depth we are talking about for other tales. The Juniper Tree.
Therefore, we should be very suspicious if anything seems to be recognisable after a few thousand years. We may be imposing meaning on stories.
Still, I hope it's true. BTW, there is a classification system for folktales that you might like to browse, the Aarne-Thompson.