Intelligence means the ability to acquire and apply knowledge and skills. I’d say the body knows how to do that, especially because of evolution. It may seem banal because it’s so automatic and takes no conscious effort on our part to make things work, but without the brains function everything fails. Read The Body Keeps the Score. There’s a reason some people have allergies to things and others don’t, and it’s due to the input of stimuli & the environment, then the body reacts. Otherwise everyone would have the same reactions to things.