I think that HADD is crap. If anything, our tendency as humans is to fail to give the benefit of the doubt to other humans let alone other species as far as intelligence and equality. Mythology is not the result of mistaking inanimate objects for spiritual entities, rather it is the natural function of the human psyche to express superlative qualities as personified characters. It is a playful, fictive process which is interpreted in a variety of ways, ranging from simple entertainment to social drama to sacred revelation and has nothing whatsoever to do with survival or evolutionary biology.
Obviously whatever we have in the way of signifying sentience is present in other life forms as well - not as an independent phenomenon but as an aspect of being a living organism as opposed to a dead one.