Selkies are also a story about how society covers up their discomfort over wrongs they cannot or will not right at the time; ie, marriage by rape.
I remember reading a fascinating theory put for by a fanfic writer called aragonite, whom I admired very much (she was on FFnet but had to take her stories off because someone started selling them on Amazon).
The theory went like this:
The area the selkie myth originated sort of 'originated'* was in the Shetlands and for anyone who doesn't know the Shetlands are an archipelago north of Scotland. Many of the islands are very small, however, people have been living on them since at least 4000BCE and probably further back than that.
These people had trade with the mainland. There are several accounts of them being excellent fishermen and also having both canoes and clothing made of sealskin. Sealskin is a) extremely warm which is good because the North Sea is very, very cold and b) extremely waterproof. There are accounts from sailors about how these 'finmen' could flip over upside down in their canoes and come up more or less bone dry again, for the most part. That made fishing an almost year-round possibility, which is great, because the more food your tribe has the better equipped you are to live through winter.
Now, tribes raiding other tribes for new members - ie, forced labour or women in general - is a very old and well-established human activity. So, if a fishermen were to, for example, see a comely young fisherlass in her canoe coming to trade and think 'well, I'll have one of those', how does he ensure she stays on the mainland once he's captured and bought her there?
Easy. He takes (steals) her 'skin'.
He either takes the sealskin off the frame of her canoe, so she can't use it to get home, or takes her sealskin clothing without which she probably wouldn't survive a trip back home. So congratulations, she's now 'married' because she is now wholly dependent on her kidnapper for food and shelter and has no means to get home unless she gets her hands on another seal skin; not impossible, there was a lot of seal trade, but if he's keeping her barefoot her odds of getting one are steep - especially if everyone in the village is kind of in on this whole thing. Or, at least, they're tut-tutting but staying out of it.
But, you know, priests and other outsiders might start sniffing around and ask about the history of the town, and they have a nasty habit of writing things down exactly as they are told (whether they understand it or not).
Kidnapping women to force into sexual slavery? Bad, uncomfortable, immoral, destroys the vibes.
A fisherman brings home a 'fairy wife'? Whimsical, funny, what a story, ha-ha don't question it, pay no attention to the logical fallacies.
And most importantly: if it's 'magical', no one could possibly do anything about it and no one was responsible. They are free from social obligations and community guilt..
Who can fathom the mind of selkies? They are just so-oo mysterious.
This is, of course, a vast oversimplification of complex history and culture, but nonetheless, there is an element in these fairy-monster-magic wife stories that kind of exist to let the wider community off the hook for witnessing a wrong but doing nothing about it.
* Shapeshifting myths come from the Vikings too, so the myth origin point is a bit muddy and might be a syncretic of a few different oral traditions
