When I was in grad school studying linguistics, I met some colleagues who had done fieldwork in the Amazon jungle. They told me about a tribe they worked with, and that tribe's concept of how souls are distributed. Now most of us in the modern world are used to the idea that souls are distributed one to a body, so if there is a human body, and it hasn't died yet, then it has a soul. But this particular Amazon tribe believed that souls are distributed one to a pregnancy. So when twins were born, the soul that went with that pregnancy was given to the first born, and that meant that the other twin had to be killed at once, Because having a body wandering around with no soul in it would be bad! It would be like a zombie!
Now, as educated, modern people, we discussed this tradition trying to inject as little cultural bias as we could into the discussion, and we all agreed that probably the reason for this conception of the distribution of souls was that in a hunter-gatherer group, a mother could afford to take care of one baby, but not two at the same time. For the survival of the group, as well as of the mother and one of the twins, the other twin had to be eliminated. But since no human being can countenance the killing of an innocent baby without some justification concerning the properties of the baby, this story about the second baby not having a soul had to be invented. This was done to lessen the guilt of the mother, the father and the entire tribe. It was a legal fiction to justify an unpleasant reality.
Now, if we had been missionaries, we might have taken a completely different attitude toward the soul question, believing that the primitive religion of the tribe was mistaken, and if they only adopted the one true religion, then they would realize, as we do, that every baby has a soul. And of course, they also would have had to adopt a modern, non-hunter-gatherer lifestyle in order to be able to economically afford this view of the soul.
The concept of the soul was invented in order to help define and distribute personhood rights to some but not all. Otherwise, all we would need to consider would be animacy. Is it alive? If so, it has rights. Is it not alive? Then it can be owned, used, and destroyed.
In many religions, non-humans have no souls. In some religions they do have souls. Whether you are allowed to eat them is one of the questions that this classification might help with. It is not a coincidence that cultures in which cows are said to have souls are also the same cultures in which eating or killing cows is not allowed. Which came first? The soul classification or the dietary restrictions? I think the concept of the soul follows the lifestyle, not the other way around.
If we go back to our own cultural bias of thinking it is one soul per human body, we can see that this idea is not entirely unproblematic, either. What about conjoined twins? One soul or two? One vote at the polls or two votes? How about conjoined twins that share a single heart, but have two heads? Is it one soul per heart, or one soul per head? Two heads, but just one body -- one vote or two? If two, who gets to cast the two votes? The head that controls the arms? But how will the other head get to choose how its own vote is cast? Will they vote on it? Who gets to tally the votes? Who is the tie-breaker?
It's obvious that giving rights to people who cannot possibly exercise those rights is in reality giving extra rights to the people who control the ones who ostensibly have those rights. So if we give all the rights of a citizen to a mental vegetable, we are actually giving those rights to his guardian.
Now, in addition to believing that it is one soul per body, many western religions tell you that the soul in question is immutable. It does not change. No matter what experiences the person has had, no matter what personality shifts the mind inside the body has undergone, the soul remains exactly the same.
In Our Lady of Kaifeng Courtyard of the Happy Way, it is Ted Sesame who gives voice to this credo concerning the immutable soul.
If the soul has nothing to do with our personality, our memories, our sense of self, our ethical standards or anything else that stems from our consciousness and changes with time, then the soul is a meaningless marker of legal personhood. Does a person still have a soul when he is brain dead? Is it the living body that gets attributed a soul -- or the mind inside that body's brain? If someone suffers a brain injury and turns from a sweet, caring person into a homicidal maniac, are we to think that nothing happened to his soul along the way?
Right now, many people enjoy movies and television programs about the zombie apocalypse. Once a person becomes a zombie, in this fictional scenario, it is all right to kill him with impunity. The implication is that his soul is no longer there, and so all the normal prohibitions concerning unjustifiable homicide are lifted. You don't have to wait till it is a self-defense killing. You can go hunting zombies. I think that one of the attractions of this kind of fiction for many people is the relief from our social prohibition against demonizing our enemies.
There's not much to take home from this, I think, besides the fact that arguments concerning the soul are not factual. You cannot prove or disprove whether someone or some thing has a soul. Stating who has a soul is in most cultures a political decision about what rights are going to be assigned to whom.
We need to be very alert to this, whenever people argue based on intelligence quotient or proof of having feelings or experiencing pain that any particular being has a soul. In most cases, this is an argument that precedes the granting or taking away of legal rights. Who gets to exercise those rights? If the rights of personhood are granted to someone who cannot stand on his own two feet and support himself, then these rights accrue to the guardian or caretaker. Sometimes the people who argue for more rights are people who plan to become caretakers. It only pays, of course, if there is public financial support given to legal persons who cannot stand on their own two feet. Hence public welfare provisions are the driving force behind expansion of legal personhood rights.