How come chemicals like alcohol can change our consciousness? Or adrenalin?
How is it that the only consciousnesses we are aware of happen to be located in exactly one human body, rather than say only the upper half of one, or fifteen humans, or any other subdivision of the universe's matter? Why is my consciousness not shared with other people's?
To me the hypothesis "human bodies produce consciousness, probably by some mechanism that's shared by lots of life but not necessarily all" is a lot simpler.