On the Origin of Changelings · 4:24am Jan 17th, 2015
We all love changelings. It's only natural; they're cuddlebugs!
But, where do they come from? Why do they need love? Why are they just so darn cute?
Originally, I'd credited/blamed Discord with their creation, through the corruption of Flutterponies. The idea seemed to make sense, and I feel it still does. But, while talking to my prereader, I came up with another theory, one that fits the show canon better and seems to have been foreshadowed in the show itself!
Note: There'll be a TL;DR at the end for you lazy folks, or if you just want the idea without all the headcanon.
But first, what do we know about changelings? Warning: Spoilers for the show and comics below!
We know they're equine, possibly another subspecies of ponies. We know they feed on love, that they have a Queen, and that Chrysalis is a bit of a twit who doesn't like apples. Yep, the show sure does flood us with info, doesn't it?
For more, we have to look at the other source of information (despite how questionable it is), the comics. One of the first things that struck me, reading the comics, was that other changelings besides Chrysalis can talk. So, they aren't mindless insects. More importantly, we see that they're loyal to their Queen, and trust in her. I don't think they say a word against her, or are punished by her, at any point.
The closest it comes is Chrysalis telling the changelings to shut up twice; once while she's trying to monologue, then again after her inevitable defeat, when they're trying so solve a riddle.
On top of that, while Chrysalis is the first one to react with fear to those things around them, the changeling beside her seems to be defending her. Until it's freaked out by the little love-balls, then it's clinging to Chrysalis like a foal and its mother, and she's holding it pretty tight in return. At several other points, Chrysalis is clearly affectionate towards her changelings.
Throughout the comics, we see they use that green crap for cocoons and building material. We also see that they treat creatures of debatable sapience (those things in the town) as little more than lunch. So, they're not exactly merciful. Chrysalis in particular, doing something horrible to one of the Huggy-Wuggies (it deserved it) to intimidate the Crusaders into being quiet and threatening to "put them out of her misery".
On to the theory. Does anyone remember the Hearts & Hooves Day episode? The one with the love potion love poison?
Let's take a look at the book in that episode:
What's the first thing you notice? Besides Prince Chinsworth, anyway. Look at the Princess. See anything odd about her?
Yep. That's an alicorn, that is. Embodiment of all three races, has wings and horn, is extremely magical and long-lived. Take careful note of that last part. Long-lived. What alicorns do we know about? Celestia and Luna, obviously, but do they seem like they'd ever been love-poisoned? Not really. Twilight Sparkle? Not a chance, considering how recently she ascended. That just leaves Cadenza... or does it? From the books, we know she was a pegasus, but ascended and was adopted as Celestia's niece after defeating Prismia, a pony who used a love-stealing spell. That leaves us with some more questions (all about Prismia), but it also leaves us with no alicorns. Except one:
Chrysalis. Twisted, but still an alicorn of sorts.
But, from her behaviour, she doesn't seem to be under a love poison herself, and it sounds like she hasn't been in Equestria many times before, and you'd think Celestia would recognise another alicorn, even if they'd changed so much.
Leaving that for a moment to go back to the story behind the poison, I'll just put a quote from the episode here:
Sweetie Belle: Apparently, some prince a long time ago whipped up this recipe and gave it to this princess he liked. He meant it to be a love potion, but things didn't turn out so well.
Apple Bloom: How "not so well" did things turn out?
Sweetie Belle: Well, there's something here about a dragon, the kingdom falling, chaos reigning... Okay, apparently it was all because the prince and princess were so lost in each other's eyes that they couldn't perform their royal duties.
So, we've got a prince of indeterminate species (could be earth-pony, pegasus, or stubby-horned unicorn. Blackjack's ancestor?), and an alicorn princess. Both affected by a love poison, both unable to perform their royal duties, their kingdom falling down around them. But, as long as they have each other, they're happy. Nothing else matters, their love their only reason to live.
A pity the prince was mortal, and the princess wasn't.
When he died (no idea how), her love for and need to be loved by the prince, unrelenting, still burning fiercely because of the poison, began to eat away at her. She remained there, in the remains of the once-grand kingdom, alone.
Until she gave birth to the prince's foal. A foal who hungered for love, as its mother did. A foal whose need for love could never be sated, like its mother's.
Not the first changeling, not as we'd recognise them, but it was a step down the path.
Foals grow up. They leave home, even if home is the ruined remains of a kingdom inhabited only by them and their mother, a mare unable to leave herself. This foal would leave, they would have foals of their own, and they would have foals of their own. Some would feel the hunger for love, some would not, until one day... one ascended to alicornhood. The first Queen. The first changeling, different from ponies in form and mind. Eternally hungry, with a need for love that matched her ancestor, the lovelorn princess.
Why didn't Celestia know about the ascension? Simple: It happened before Celestia or Luna were even born.
From her, the first Queen, Genesis made flesh, came a call. Those who were descended from the lovelorn princess, whose blood still carried the love poison's taint strongly enough, were drawn to her. The magic of the alicorns is powerful and strange, affecting those around them, and unborn foals most strongly. More were born like her, the beginings of the changeling race, from parents who were only ponies on the outside. Neither earth pony nor pegasus nor unicorn, but something new. And from the strangeness of her magic, the Queen's own daughter would be born like her, an alicorn.
Thousands of years later, we have Chrysalis, latest in a long line of of Queens, alicorns who aren't ascended, but born. The truth of their race is lost to the mists of time and a kingdom long turned to dust. The changelings themselves, long-parted from their pony cousins.
And that's my theory about where changelings come from
I know it's got some flaws, and maybe a few holes, but so do changelings!
At the very least, I hope it was interesting and got some of you thinking.
There's some things I didn't touch on, like the "nice" Chrysalis from the comics, or more detail about Prismia (haven't read the book yet), but there's enough to come up with some more interesting ideas.
tl;dr: Changelings exist because of the love poison.
That is a legitimately amazing theory...
SOMEONE SEND THIS TO THE_CHANGELING_PRINCE_2!
I mean, at the very least, I'm sure he'd like to know it.
Dude, I can buy this.
Also, if you're interested in a canon-set showing of who Prismia could have been, as well as my own interpretation of how changelings were created, I highly recommend my story, Essenza di Amore.
Of course if you're not one to go for blatant self promotion, check out Equestria Daily. they just reported on a new, specifically villain-centric line of comics, each focusing on our show villains' back stories. No telling exactly when they'll be out but they look very promising.
but pls read my story, I spent 6 months writing and perfecting it
I'm dead tired, and you still manage to wake me up and get me understanding things!
This is an excellent theory, and one I'm cataloging as "Plausible and believable." Now, I believe my bed and cat are calling! Cat louder than the bed, obviously. 
Oh, and one more thing; I have breached 2,000 words on the Hearths Warming Event story, and I'm right after what I think is my halfway mark! Hopefully it'll be in your hooves by the end of the month!
Hm, interesting!
I do not think I have ever read a theory for anything fictional that I have liked as much as this one.
Honestly? This comes off as quite believable. Not my personal choice for an origin story but a likely one that fits with the shows themes. Linking back to the shows previously mentioned lore is something I feel has been done quite a bit recently and I wouldn't be surprised if the show does link Queen Chrysalis back to the Hearts and Hooves day princess, perhaps not in the same way but certainly in a similar fashion.