Unless you assume some magic/soul/etc, then a human brain is a proof that there exists a non-impossible algorithm that learn to be a General Intelligence, and it can run on non-impossible hardware.
Yes, I assume a magic/soul/etc. and I believe that the human brain is not stand-alone in creating intelligence.
Check out this exciting video for discussion on how 'thinking' can happen outside brain.
https://neurips.cc/Conferences/2018/Schedule?showEvent=12487