Our world is not perfect, and I don't think it ever will be. But we are certainly doing better than 1000 years ago. Look at # of death in wars per century, you will get a picture. Look at democratization, human rights, slavery, treatment of women and children, health care, science and our understanding of our environment... we have come a long way.
About soul accounting & reincarnation:
As I have understood it, reincarnation has its earliest roots in Hinduism ( and later in Buddhism). Anyway, it is a belief, and not a scientifically proven fact.
But as per belief...
The spirit or our consciousness is one and the same, like a vast ocean, but the waves on it are many, fleeting and recurring. A soul is like a wave that manifest on surface of ocean, and if left unresolved it resurfaces in another sapce-time as new manifestation. Also it is not a single discrete packet, but a continuation. And one wave (soul) can split in many, and many can emerge as one. Hence patterns of reincarnation can be countless. A man can become a tree, stone and a dog and all those who died in a single plane crash can come back as one single personality. Therefore this one to one accounting of souls is mere approximation for popular understanding, but not an accurate reflection of the doctrine.
I'll give a mythological example in Hindu scripture Ramayana. It is more of a metaphor, but makes the argument I am trying to make. Here Lord Vishnu, his consort Lakshmi, and "his bed" (a huge snake SheshNag) all together reincarnated as Rama, and his 3 brothers and his wife Sita. Thus 3 became 5 for the purpose of drama that unfolded in Ramayana.
Your Adam and Eve reference from point of reincarnation is very interesting. One way to look at this could be to see Adam and Eve as 2 powerful waves emerged on the consciousness and rippled further into billions of patterns as planets, starts, people, trees, plants, animals and entire cosmos.
Again reincarnation is belief, and stories associated with are metaphors for larger understanding of life as movement is much longer journey than meets the eye.