According to Hinduism, a soul incarnates in several forms, in several realms - not just as an Earth being. A soul could incarnate as a tree, a bug, a deer, a rat, a rabbit, a cat, a human and so on.
I personally do believe in reincarnation. And my personal belief about whether a soul can incarnate as a non-human before/after a human incarnation is as follows: Yes, a soul can incarnate in many forms. I do not believe that the human form is so special that a soul incarnating as a human could not take other incarnations (in past or future lives) as other beings.