True native Americans have the deepest respect for "nature." Their word for God union or self realization was "true hearted." They saw and understood much of the natural condition of how to live in harmony with nature but did not have the scientific language of today's scientists. They saw the living forces and living energies of nature and creation and simply called them "spirits."
Lobsang Rampa states: Humans in their conceit and overweening sense of superiority think that they alone have a soul. Humans think that only humans continue after life, after death, and into another life.
Many of the ancient races worshiped Nature Spirits. They were not so far wrong because there are Nature Spirits, and they are quite as important as Nature Spirits.
A human is a lump of protoplasm plasm which has a soul some times called the over soul or Holy Spirit which tells that lump of protoplasm plasma how to operate. How to grow, in the same way trees have Nature Spirits, spirit entities who look after that tree. Animals also have spirits, souls, if you like. And it does not at all follow that because an animal cannot speak English or any language, that the animal is Dumb. Many animals have characters in no way inferior to the best of so called humans. (From the root word Humane).
For your own evolution, then, remember that there are animal spirits growing and evolving on different lines from humans, admittedly, but in no way inferior to humans. They are distinct and quite separate lines; Humans never reincarnate as animals, animals never reincarnate as humans. They are quite, quite different lines of growth.
See also: the chapter on Drugs (Social).