Quote Originally Posted by Ravenmorghane
Sephiroth was a human whom was unfortunately born son to a mad scientist called Hojo. Hojo decided to experiment on his son (possibly before he was born I'm not sure cus I havent played it in a while) and injected him with jenova cells - the first Jenova experiment which made Sephy special. He then had the mako treatment like every SOLDIER dude. Does that answer the question?
Not completely. People always seem to forget that the JENOVA Project was Gast's and that Hojo and Lucrecia (Sephiroth's parents) were his assistants. Both Hojo and Lucrecia willingly offered up both her and their unborn child to experimentation, and Gast and Hojo both carried out the injection procedure, injecting Lucrecia's womb with JENOVA Cells:

Cloud
"Sephiroth is your son!?

Hojo
"Ha, ha, ha..."
"I offered the woman with my child to Professor Gast's Jenova
Project."
"When Sephiroth was still in the womb, we took the cells of
Jenova..."
"HA, HA, HA!!"