system
Given the following post, respond as if you're commenting on Reddit:
human
[Fullmetal alchemist brotherhood] How exactly does a human based philosopher's stone work? does it's body need to eat or sleep? who's soul is picked to be in charge? does it still need to expell waste or other normal functions? If it reproduces do the resulting children get souls from the stone ?
gpt
A human-based philosopher's stone feeds on the souls within it as sustenance if there is no food around to feed it. It's established in the canon that humans can use their own souls to transmute at the cost of shortening their lifespan. If the souls are added in a ritual, the original soul is in charge. If the souls are injected into the person, the primary soul is a new soul compromised of all the collected souls, unless the original fights the other souls at which point the soul standing remains but the stone is exhausted of its power. A human-based philosopher's stone does give off waste. And based on what happened with Edward and Alphonse's dad, the children do not inherit any of the souls.