Just curious.
How about a Dwarf and a human?
No, because one of them is fictional.
If you’re talking about within a fictional setting then the rules are whatever the author wants them to be. If he wants a human to interbreed with a dragon, then it’ll happen.
In the context of Tolkien’s stories, hobbits were humans, just a peculiar subpopulation (like the Druadain). There might be size-related issues that would make reproduction between Hobbits and Bigs difficult, and of course there’d be social and psychological barriers, but other than that, they’re the same species and should be interfertile.
Dwarves, however, have an entirely different origin than humans (or, for that matter, elves). They were created as automata of a sort by Aule, one of the Valar, who grew impatient waiting for the Children of Illuvatar (the Elves and Humans) to appear in the world. Illuvatar scolded him for his impudence, but when Aule repented, he gave them the fire of existence and named them as adopted children. So we can reasonably say that Humans and Elves are more like each other than either is like Dwarves. And while there were a few couplings of humans and elves, they almost never resulted in children, and then only in the most extraordinary of circumstances, so we can extrapolate that humans and dwarves would not be interfertile at all.
If, by chance, you’re thinking of Homo floriensis, the recently-discovered relative of our species which may have out-survived even the Neanderthals, we can’t know for sure, since they’re all extinct now (we think). But as a rule of thumb, animals in the same genus but different species can typically interbreed, but usually don’t do so given the choice, and the resulting offspring are often sterile, like mules. So it wouldn’t be a stretch to assume that the same applies to H. sapiens and H. floriensis.
As Chronos noted, the remains of a probable third species of humans some call the “Hobbit people” was discovered in Indonesia a few years ago. It is almost certain that they existed alongside homo sapiens there so the question isn’t completely ridiculous.
This question involves fictional beings. I’ll move it from General Questions to Cafe Society.
Gfactor
General Questions Moderator
–Animated Gandalf to Animated Samwise
Transcribed from The Return of the King (1980).
Youtube clip (at appx. 5:09-5:51)
So there’s your answer, courtesy of Rankin-Bass.
Dwarves, on the other hand, couldn’t even breed well with each other. They had the misfortune of being created with drop-forged chromosomes.
- Furbasol (Sindarin) ‘pervert (with an unhealthy interest in interspecies sex)’. Devised by Daeron as a nickname for Beren.
Tangential, but… If you want to go the D&D route and substitute ‘Halflings’ for ‘Hobbits,’ I’d have little doubt that it would be possible. Size could be an issue, but that’s what Polymorph Self is for. In fact, looking at the core rules alone, it seems damn near anything can breed with damn near anything else. I think one of the 3.5 supplements even gives guidelines for crossing any species.
So just pretend the Tolkien estate is kosher with all that. 
After a buddy & I saw Jackson’s FotR at the theatre, she wanted to see the Rankin-Bass RotK. (I warned her there’d be splenty of spoilers. She didn’t care. She was surprised to see Gandalf again.
Her: I thought he died!
Me: Told’ja he was a semi-Christ figure.
Her: rolls eyes, as she is wont to do when I bring up Christ, but has to concede this one Yes, you did.
Anyway when Gandalf says-
"And if you keep the Book of the Hobbits as Frodo asked, ages from now, when your stories are still told, will be those humans who might well wonder, “Is there Hobbit in me?”
Her: Ted, might there be Hobbit in you?
Me: I’m fat, I’m lazy & I live in a hole at the end of the hall. I think the case is clear.
There’s an entire section that the dear professor omitted from the original tale, having to do with the sex trade and live shows at Bree. In fact there are rumors that some of the Gamgee brood, whose enormous genital dimensions were legendary, participated in a show called “the wee one’s happy human wife” or something of that sort.
I’m just glad that Jackson decided to leave that part on the cutting room floor
“You WANT a little Hobbit in you?”
Pervy hobbit-fancier!
**Terrifel **was joking of course. That RotK has almost nothing to do with Tolkien. 
For the record, Tolkien hinted in the forward that Hobbits actually dwindled even more in size. It seems unlikely they would grow larger going forward in the Fourth Age.
Merry & Pippin of course were exceptionally tall due to a magic-like effect of drinking Ent-Draught.
As mentioned, Dwarves are much further from humans and almost certainly would not be interfertile.
Footstool of a Took!
Hey! I can assure you that I was addressing the question with all my customary gravitas.
The question was whether Hobbits and Men COULD interbreed, not whether they ever DID interbreed. Of course there would have been social resistance on both sides. Nobody wants to be labeled a furbasol.
As far as I know there are exactly three known couplings of humans and elves: Tuor and Idril, Beren and Luthien, and Aragorn and Arwen. All three of those resulted in children.
Actually there was at least one more and it could be argued that Aragorn and Arwen don’t count. Arwen was numbered among the Half-Elven (Peredhel) and was neither elven nor human despite being 25/32 elven, 6/32 human and 1/32 maia.
The line of Dol Amroth had a Sindarin Elf (Mithrellas of Lórien) in it and it is well possible there were others not mentioned.
Yes. Hobbits WERE human; they were a subspecies of Man.
Edwardian that he was, Professor Tolkien was discreet on certain things, but it’s clear that Farmer Cotten was afraid of Rosie and his wife being raped by Sharkey’s men. I think it’s safe to say that happened more than once before Merry & Pippin came back to put things right.
Wouldn’t have worked. She’s quite the sapphite & that would only have made her gayer.
Which really puts a whole other spin on all those unusually strong, blond-haired Hobbit-children born in 1420…
I hadn’t thought of that, but you’re right. Nonetheless I’m going to go with the mallorn explanation.