michel said:
Do you have any idea in how they differ?
Not in very specific terms. I believe that since we are created in God's image, human beings have a spirit that is more like God's. We have the ability to be able to distinguish right from wrong. In the Garden of Eden, after Adam and Eve ate the forbidden fruit, God said, "Behold, the man is become as one of us, to know good and evil." Animals, I don't believe, have the ability to make decisions of a truly moral nature. Maybe that's why I like them so much. I don't believe they can be "evil." They sometimes do bad things, but I would attribute these things to instinct or to the will to survive, or -- when they have been abused by people -- out of fear. Because they don't have a moral consciousness, I don't believe they have the same divine potential we human beings do. It kind of gets back to my belief that in order for us to be able to progress spiritually, there must be opposition in all things. They can't know (at least not to the extent we can) the difference between good and evil, so their progression is somewhat limited. On the other hand, they do have emotions, and anyone who says they don't is just plain wrong!
As to how this distinction extends to plants, I'm less certain. But, the fact that we know plants can be either alive or dead does, to me, imply the existance of a spirit component. Also, that's part of LDS doctrine, though none of our leaders have ever elaborated on it. We believe that God created the spirits for all His creations before He created them physically. So, once again, I believe this extends in some way, to plants. I've heard of scientific studies in which plants in separate "test groups" were exposed to different types of music. They responded differently to classical music than they did to hard rock. All I can really remember about the study was that the group of plants that were in a room where classical music was being played, eventually started growing towards the source of the music. I don't know that it really proves anything, but I found it interesting anyway.
I've done a very small amount of research into early Christian beliefs concerning whether or not animals have souls, and did learn something quite interesting. For instance, one early Christian document, "The Secrets of Enoch," states that animals will appear at the bar of God's judgment to accuse human who have wronged them. Obviously, this is not Christian "doctrine" today, but it's possible that the ancient Christians believed this to be true. Also, in the Bible (in Revelation 4), there is mention of four beasts who were seen by John as praising and glorifying God. To me, that sounds like they have immortal souls. I think they have far greater wisdom than we often give them credit for.