Hobbits?

[Selador]

The origins of Hobbits remains a mystery that I think Tolkien preferred to leave unsolved. I think that it is better left that way. But really, the existence of Hobbits is a sort of an historical accident.

Tolkien's letters make it clear that he was content to close the book on Hobbits after he had written the book The Hobbit. He really never intended them to get pulled into the universe of his greater mythology and was very resistant to any sort of sequel. But while JRRT wanted to flesh out his histories of Men and Elves, his publishers were insistent that a sequel involving Hobbits be written. So, we ended up with a masterpiece that encompasses both.

As you say, Tolkien had already established the origins of Elves, Dwarves, and Men. Now he had to squeeze Hobbits into the mix somewhere. He does so by making them sort of cousins of Men - a branch of the race known specifically as the 'human' race (as Tolkien tells us in his letters). I think he made them akin to Men because he saw both as purely non-magical beings, unlike Elves and Dwarves. But as far as I know he never tells us exactly how or where the Little Folk came upon the scene. I guess they must always remain just Eru's little secret, that in the end becomes the key ingredient to the fulfillment of his plan.