Something me and a friend have been discussing for a while now is the odd similarities between the Dementors and the Lethifold, and I think that the best explanation is the simplest. Dementors and Lethifold in fact share the same race.
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SPOILERS ARE FOR ANYONE WHO HASN'T SEEN THE TIME MACHINE MOVIES OR READ THE NOVEL!
If you've ever read The Time Machine or watched the movies then you'll probably get a general idea of what I'm talking about. For those of you who don't, in the story, the main character uses a time machine to go into the distant future to see how humanity has advanced.
In the future, he stumbles across two strange races of creatures. The Eloi are completely childlike and have little to no knowledge of anything outside their temples. And the cruel and cannibalistic Morlocks who dwell deep underground and run complicated machinery in order to better prepare the Eloi on the surface for food.
Eventually, the Time Traveller comes to the horrifying realization that the Morlocks and the Eloi are in fact, descendants. Humans had long ago evolved and branched out into two distinct subspecies.
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So you can probably guess where I'm going with this. I think that centuries ago, probably before humanity as we know it was even around, there was some other race that roamed the Earth. Eventually, something happened. Maybe some kind of cataclysm, or maybe it was just evolution doing what evolution does best. But eventually, this race evolved and branched out to become what is now known as the Dementors and the Lethifold.
