The way I understand the term substance dualism is that there exists the material realm made of atoms and an immaterial realm made of, for want of a better word, spirit. I believe there are many aspects of humans that establish it in particular the existence of libertarian free will, as opposed to compatibalism (I make a case here https://forum.freecapitalists.org/t/does-praxeology-imply-that-there-is-no-free-will/12964/26 )and as you point out emotions themselves would lend itself towards substance dualism since without it there cannot be a subject to feel, only atoms exist as my signature states.
Naturalistic evolution cannot account establish a foundation for truth ascetaining senses, merely survival ascertaining senses; to survive doens’t mean you have true beliefs. To say that the question is unanswerable is just atheistic hand waving. Now treating them as ultimate givens is correct however only in an epistemological sense- we know truly that these parts exist and exhibit these criteria; however it doesn’t follow from that we cannot create a solid foundation as to how they do exist.
It depends of course what you mean by observe. If you mean by the 5 senses then no except if you lived in Palestine in the 1st century AD, at a burning bush etc ie non-repeatable events. With introspection, conscience etc you can reflect on his existence and via prayer can actually commune with him.
As to why he comes in? A brief argument: The universe came into being (the idea of it being infinite in an actual sense is absurd). Therefore a creator exists. Now to qualitatitively differ from one another we need something other than matter to be the true subject. Therefore the creator creates the qualitatively seperate souls which are united with a body to make it our body. Now I am open to the idea that animals have souls although they probably aren’t rational and exibit qualitatively different attributes than human souls.
Taking the nature of acting man without a consistent metaphysical underpinning.
Correspondence.