User blog comment:LastationLover5000/Fairy Tail 301 - In Which Hiro Has Been Reading My Things (The Dragon King)/@comment-3549833-20120928211202/@comment-4666155-20120928211958

Nah Per, Zealconis (it's ZEALCONIS, even the ACTUAL WIKI is calling him that), is wrong. I'm trusting Usopp's research on this one. Zealconis has probably never taught a human anyway, he wouldn't know the side-effects of teaching a human Dragon Slayer magic. And the way it was described, even if he was right, it only seems to affect humans that are particularly malicious, as Acnologia in human form was said to drink the Dragon blood, no?

And true, that would explain it. Either way, no Dragons from Humans >-< (But Humans from Dragons are just fine)