Board Thread:Questions and Answers/@comment-34129530-20140808152003/@comment-679780-20140809042822

Also, you ask how Shadows creation is possible "without hedgehog or Sonic's DNA?"

It's true that it is impossible for Shadow to have been created after Sonic's DNA but that doesn't mean that there arn't other hedgehogs out there. Gerald Robotnik is Shadows creator, Black Doom contributed his blood with altering the DNA and no one cares who is is the genetic doner of hedgehog DNA to the project for Gerald to tinker with.