We don’t always have a lot of information about ancient myth and how it survived. Even when stories were relatively well-documented, as in the case of Greece and Rome, you can’t always tell where they came from or how they evolved into the form we know now. And when the tales were written down by people who did not see them as religious? That adds a whole additional layer of intention to see through.
The Scandinavian and the insular Celtic myths that we know were written down long ago, generally by people who were at best dispassionate and at worst antagonistic toward the beliefs those stories reflected. The tales in the Elder (Poetic) Edda were copied down by Christian monks–how much in them is an accurate transcription of what they knew or heard? (That said, how much did the stories change among those who believed during the pre-literate centuries?) In the Younger (Prose) Edda, Snorri’s intent was primarily the preservation of a literary form rather than its content, which provides a different set of difficulties. In both cases, however, the conversion had been recent enough that a certain amount of the Norse myth was maintained. The Celts were not quite so fortunate, and the Irish legends (and especially the Welsh ones) can be difficult to parse for religious content. The stories, however, are often still there.
In the Kalevala we have a comparatively modern (and comparatively well-documented) instance of surviving ancient tales making their way into the modern record.
The Finns of the time (like their Scandinavian neighbors) had not been pagan since the 12th century BCE or so. and by the mid-19th century any myths in their original form or forms had long disappeared. What still existed, however, was a long-standing tradition of story-singing in which one could hear echoes of the ancient Finnish pagan faith. This oral tradition existed for centuries, but by the 19th century the practice was dying out, and with it what was known of ancient myth.
We can thank Elias Lönnrott for the survival of much of what we know about Finnish folklore and myth, as he was the author of the Kalevala, the Finnish national epic poem. The 19th century in Europe was a time of political upheaval, of smaller and less powerful lands reacting to many years of having been occupied by larger and more aggressive nations; in the case of the Finns, the occupier was Russia (they did not declare their independence until 1917). One way in which the smaller lands, such as Hungary and Poland as well as Finland, asserted their identity was through their native folklore and myth. The Kalevala was an example of this–a reminder to Finns of their unique culture.
Lönnrott travelled far and wide throughout Finland, going from place to place, listening to the story-singers and writing down their tales. This research took years and resulted in a large body of work and a wide variety of songs (including many stories with more than one version depending on the region and the storyteller). It was an impressive feat and one which resulted in the survival of many stories and lore that otherwise would have been long lost.
With reference to Lönnrott I use the word “author” mindfully and with intent, because in assembling his poem he used enough poetic license that the work as a whole can be considered his creation. He sometimes combined characters (the Kalevala’s version of Lemminkainen, for example, includes characteristics of several other heroes as well), renamed them or created them out of whole cloth to be featured in existing tales (such as the unfortunate bride Aino, who is never named such in in the original songs).
This isn’t intended as a criticism of Lönnrott, by the way; while saving the stories was one of his goals, it was not the only one–and the creation of the Kalevala, Finland’s national epic poem, was itself a uniting force. What the Kalevala is not, however, is an accurate retelling of ancient Finnish myth or of the folktales that held its last remnants.
However, the wonderful thing about the Finnish stories is that we don’t only have Lönnrott’s final work to rely on. We also have his extensive records and transcriptions of the songs and stories he tracked down so long ago. We know much of what, in the Kalevala, is Lönnrott’s own work; we can tell when he changed things. We have the original 19th-century songs and you can actually go in and compare different versions of the same stories.
I absolutely recommend reading the Kalevala or any of the transcribed Finnish songs. The stories are wonderful, and the rhythm of the poetry is beautiful and unique.
Kuusi, Matti, Ed. Trans. Keith Bosley. A Trail for Singers: Finnish Folk Poetry: Epic Finnish Literature Society: Helsinki, 1999.
Lönnrott, Elias. Trans. Keith Bosley. The Kalevala. Oxford University Press: London, 2009. Kindle edition.
Pentikäinen, Juha Y., Trans. Ritva Poom. Kalevala Mythology. 2nd ed. Indiana University Press: Bloomington, 1999.