Is it me or does the Hive look to be the "space zombiefied" or mutated vesion of existing races. Sort of like what the Flood were in Halo. From the few pics out the it looks as if they are mutated version of the Fallen, Humans, and even the Cabal. Similar to what the Reapers were in Mass Effect 3.
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idk. I think they do use bodies of fallen victims, but only after modification, like the three green eyes and what not.