[Keeper of Dol Guldur]

The idea of hermaphroditic dragons is an appeasing one, but I was always under the impression that Tolkien's dragons weren't especially different from those of Medieval Legend.

Where did Glaurung come from? I definitely don't think he was a tortured Eagle or anything of the sort, after all dragons may have rivalled eagles but there are many more differences than say, an Elf and an Orc. Rather, I'd take more a story like how Sauron bred his Nazgul's Steeds. Some ancient creature (dinosaurs, anyone?), still existed in the pits of Angband, and Morgoth, using black magic, did horrible things to them (like splicing with huge wings and so forth) and inhabited their bodies with Fell Spirits, extroardinarily powerful ones. Clearly not the Valaraukar, but something of that kinship - spirits of fire and ruin that hailed from the beginnings of Middle Earth itself, not unlike a Bombadil, a Goldberry, or other more 'Fairy-Tale-ish' sorts of things to be found in Tolkien's world.

Obviously the concept of bloodlines were important to Tolkien and in the Lord of the Rings and it's companion books. Glaurung being the first, was "Father of all Dragons" because he was the first finished product of all these freak reptiles Morgoth bred, inhabited with a fell spirit and allowed to grow beyond nature's original intentions. Clearly there would have been females too, just none anything within the realm of Glaurung, and all more nesting creatures. It's likely before he was unleashed on the world, Glaurung had a whole herum of female reptilian monsters, with nests of eggs the likes of which Ancalagon, Scatha and Smaug all came from, although each would have been subject to being interjected with one of the evil spirits of Morgoth's servitude whether while in eggs, or just after hatching, or even after a certain growth.

Obviously the Nazgul's steeds weren't possessed by evil spirits, they were just steeds, whereas dragons spirits were likely the reason they grew into the terrifyingly powerful creatures they were.