First, reincarnation is always progressive. Man never reincarnates the body of lower animals, no matter how animalistic his previous life had been. Man always comes back a little better than before.
2nd, we reincarnate not necessarily because we are bad but because its necessary to attain perfection. All must undergo the process until perfection is attained.
If its true that we have lived before, why we don't remember our past lives?
* Because the process of earthly rebirth of entering the physical plane causes a drowning out of our memories, just like the fact that we don't remember our dreams when we wake up.
Source: Soulmates, Karma, Reincarnartion by Jimmy Licauco
