Metaphysical / Paranormal event
The first sorcerers began to be born when the dragons began to reach adulthood.
The first sorcerers were all draconic bloodline sorcerers, and were born within range of dragons' regional effects. They learned their powers through instinct and trial and error. Some, recognizing these powers as draconic, sought out education from the source, although the dragons were as confused by their existence as the mortals were.