C'est dans les Letters n° 158 (surtout dans la note de celle-ci) et n°319 que Tolkien en parle.
Letter n°131 (probablement fin 1951) : "[...] In the middle of this Age the Hobbits appear. Their origin is unknown (even to themselves)* for they escaped the notice of the great, or the civilised with records, and kept none themselves, save vague oral traditions, until they have migrated from the borders of Mirkwood, fleeing from the Shadow, and wandered westward, coming into contact with the last remnants of the Kingdom of Arnor[...]"
* "The Hobbits are, of course, really meant to be a branch of the specifically human race (not elves or dwarves) - hence the two kinds can dwell together (as at Bree), and are called just the Big Folk and the Little Folk. They are entirely without non-human powers, but are represented as being more in touch with 'nature' (the soil and other living things, plants and animals), and abnormally, for humans, free from ambition or greed of wealth.[...]"
Letter 319 du 08/01/1971: "...my 'hobbits' were in any case of wholly dissimilar sort, a diminutive branch of the human race..."
NB: les Letters donnent quantité d'autres détails sur les Hobbits. Il serait troip long de les citer tous ici.
Silmo