> You only respond to external stimulus or sensations from your body.
Oh really? So I never spent time simply pondering why this universe exists? Or why I like the color blue more than green?
> In my layman's understanding of biology, the only difference between human brains and other mammalian brains is neuronal density; all the structure is the same as far as I've read.
And yet humans are different. That's the puzzle. You can't say "I've solved the puzzle - there is no puzzle!" because there are obvious differences that you can't simply ignore by saying "I don't understand".
It doesn't work that way.
> If you have to keep believing humans are somehow special, then associate that specialness with being the only creature with highly dextrous appendages that evolved with access to trees and metal that also farms.
No thanks. I choose reality instead. Where humans are in fact special, they have self awareness and language, and the ability to argue on the internet.
You can go on imagining yourself as a body without a mind if you like, I choose different.
Go read Blindsight by Peter Watts, and ponder why we have a mind - the book will show you it doesn't have to be that way, yet it is.