If you wish to make an apple pie from scratch, you must first invent the universe. — Carl Sagan The existence proof argument for general intelligence, the idea that artificial general intelligence must be possible because human general intelligence exists, would not even be conclusive if by artificial general intelligence we meant a brain grown in a vat — the existence of a thing does not prove that it could have come into existence in any different way — but it’s absolutely absurd if by artificial general intelligence we mean a computer running certain software. The existence of anything does not prove that a computer running certain software could perfectly simulate that thing. This is not even true for many things far simpler then a human brain, such as a double pendulum.
"the existence of a thing does not prove that it could have come into existence in any different way"
If you accept laws of physics and don't ascribe any metaphysical properties to the thing - then yes it does. It might be unlikely, but you can just put the atoms in a proper configuration and you will have your thing.