No Apologies
Half-dragons are weird.
I mean, dragon and human anatomy isn’t exactly compatible. The parts don’t really fit. And there’s a size issue. Do the humanoid mothers lay eggs? That doesn’t seem physically possible.
Ostensibly, shapechanging comes into play, but not every type of dragon can alter its form into that of a human. That power is mostly limited to metallic dragons. Or the oldest of old dragons, who don’t strike me as the sort to want to fool around with tiny mortals.
You know, apparently the ancient Chinese had this belief that jade (the mineral) was the dried semen of a celestial dragon.
That’s a possibility if you want to make half-dragons but don’t have a willing dragon; you could use an artificial-insemination magical ritual instead, with jade or some other jewel as a material component.
Now if you’ll excuse me, I have to go write this idea down; a noble house who used their family jewels (no pun intended) to perform a ritual to imbue their descendants with the power of dragons.
I agree, half-dragons are weird. Especially after 3.5 granted the template quality to the thing, so you can make a half dragon out of… anything, like a half-dragon-half-treant. Not just puny humans, but actually every creature that moves and breathes. Before that I didn’t know the dragons were SO horny and ready to fuck around (literally) this much…
It is magic, and dragons are made of magic.
Seriously, only those who can take an appropriate shape come into half-anything offspring,of course. And sure every type of dragon can alter shape, even if you stick to the old “everything by color” stuff which i never did, just think of the class levels dragons can have. Shapeshifting is really an easy thing.