Theologically, if a stem cell splits into two cells, is that a duplicate soul or a totally different soul?

Interesting, if life and creation begins at conception then twins must share souls.

If one twin sells his soul to the devil to become a famous lounge singer, what happens to the other twin?

Ah, regretfully the religious ones have it there way again. Some seem to think a soul is mysteriously implanted into an embryo at conception, and there lies another stumbling block to medical sciences advancement. But, cheer up, recent stem cell research has developed new stem cell lines from old existing ones. There may be hope yet. I agree that it does hinder the advancement of medicine but with determination and much hard work progress is being made despite the short sightedness of religion.

Recent digital film evidence indicates that there is never a time when most organisms are only one cell (there remains a question in the case of parthenogenesis). By the time the DNA from each parent combines, the cell has already divided. Some scientists suggest this two cell stsrting point may give the membranes contact with another cell that might allow for differentiation to occur (a point of reference to expand from) that a single cell would be missing.

Do you mean an embryo or pre-embryonic cell-bundle?

The obvious answer would be a different soul, since twins are separate people. That said, twins do seem to share personality traits and be able to understand each other far more deeply than "normal" siblings.

This is assuming that souls exist etc.

a stem cell isn't a person. But embryonic stem cells are gathered from a Human Being. Scientifically, can an embryo be anything OTHER than a Human Being?

You also have to keep in mind that these two separate clumps of cells can merge back into one.

So one of the souls got taken out to the Recycle Bin

That is a great question.

I don't think theologians know for sure, that is probably why they are against it is because they are unsure, and may not interrupt the sanctity of life by unnatural means.

I would have to say one person otherwise everybody who doesn't have a twin has a died twin. Think about if you have a twin then two cells developed if you don't have a twin you have a dead twin.

1

It all depends on whether it's naturally conceived- if so they both have souls.

If it was artificially conceived neither will have a soul.