Found this epic theory that Sonic is an Alien, he's the one born on Ark, the one who lived with Maria.

Found this theory from five years ago.

https://www.youtube.com/watch?v=vYBc-UldAcY

Apparently, it means that Shadow's memories of Maria are actually Sonic's memories.

This explains the logical hole - that Gerald said he has created Shadow to avenge Maria. Yet Shadow has memories of living wiht Maria.
So it means that Sonic is the ultimate lifeform that Gerald has created. While Shadow is the copy with similar capabilities.

It explains why Eggman is always after Sonic. Always tries to harness Sonic's Chaos power. Either by creating Metal Sonic, Mecha Sonic... trying to control Chaos or Shadow.