Here's a banana for you to munch on while pondering!
On a serious side though, I actually think what you are bringing up are very good questions. Kind of like, what came first, the Chicken or the Egg?
I was watching a program the other night where scientists are looking at space rocks from Mars and the genetic DNA of the fossils within .... where they are almost identical to DNA patterns here on Earth.
With that said, I don't discredit summations of animals having spirits because, in finality, they too are living beings. And, if you look long enough, over centuries of time with accounts of different areas, all have stories of animal spirits - regardless of color or creed.
As for demons.... I personally think the term is overused... kind of like the 90's craze with Ritalin. Demons were never human or animal; they are a species of their own from a time long before any of us can even begin to fathom. I don't discharge demons from mind, but I believe that the majority of negative interactions that are experienced are negative imprints left behind or by a spirit whose unfinished business still exerts an emotion of anger or hatred or to cause harm.
To look at the spectrum of Heaven and Hell, or however it is coined per location of a particular society, I look at it as being all around us - like air. We can't see it,but we know it's there. As a little child my child brain said Heaven was in the clouds and hell was at the core of the earth. As an adult, I put it as everywhere, on a different plane from us, but nonetheless, here.