Plotinus, if the mind is immaterial then how can brain damage be explained? If your soul could go on communicating after your whole brain was gone, how could damage to the left cerebral hemisphere take away your ability to talk? And damage to the frontal lobe has been known to change someone's personality entirely. How do proponents of dualism, especially religious ones, reconcile such observations with their beliefs?
Simple: if you believe in the soul you can say that the brain acts rather like a radio receiver. If the brain is damaged, it won't pick up the soul's broadcasts properly. If the brain is the (main) point at which communication between the body and the soul occurs, then clearly damaging the brain will damage the communication between them, even though the soul itself remains untouched.
Most would just call it one of the mysteries of life and God.
God set down the principle of the soul in the first chapter of Genesis. Most just relegate that to meaning life. Later it was written that the soul that sins will die. Not the human or physical, but the soul. Yet some would just say that is still just human life. Up until the time of Christ, it was accepted that the body went to the afterlife. Yet no one actually saw the body leave, in fact most bodies that survived, even if they were actually prepared to go somewhere can still be seen somewhat in tack even today. So what went to the after life? What is supposed to die, yet lives on when the body dies?
It was not until recently with the advent of monism that humans questioned the fact that this immaterial thing surely must not exist, seeing as how it has no substance. What are we trying to reconcile? We know that the ability of personhood is effected as to the health of the physical brain. It would seem to me that monism just relegates the whole activity to the product of evolution. If one accepts evolution and throws God away they have already sent the soul along with him. One can still be moral and create a religion void of all that.
I don't think this is quite accurate. The notion of the soul, in the sense of an immaterial thing that survives the death of the body, was very well developed in Greek philosophy long before the time of Jesus. It's clearly taught in Plato's
Phaedo, where Socrates tells off his friends for mourning his immanent death, on the grounds that only his body will die, and not his soul. In Judaism, and indeed in most of Middle Eastern religion, there was much less sense of a soul; rather, people thought of life after death - to the extent that they did think of it in bodily terms, as you say. This developed in Judaism into the doctrine of the resurrection of the body, a doctrine which by Jesus' day was held by some Jewish groups (notably the Pharisees) and denied by others (notably the Sadducees). Since both Jesus (apparently) and Paul (certainly) were closer to the Pharisees on this, the doctrine became part of Christianity too.
You cite Ezekiel 18:20 ("The soul who sins, he shall die") but it is a mistake to think that the word translated "soul" here has the same overtones as the English word "soul". The Hebrew word is "nephesh", which simply means a living (or, more literally, breathing) creature. It has no sense of immateriality or something distinct from the body. It is used throughout the Old Testament to refer to living creatures, including non-human animals, e.g. Leviticus 24:18. Sometimes it refers to dead creatures as well, including corpses, e.g. Numbers 9:6.
The notion of the soul is present to a slight degree in the New Testament, largely because Judaism had by this stage picked up some influences from Greek philosophy; but it became more important in Christianity later on because of the direct influence of Greek philosophy, notably Platonism, the philosophical school that most of the early Christians liked the most. Note that other schools of Greek philosophy denied the existence of a soul (in this sense); the Stoics were materialists and thought that the soul is physical, and the Aristotelians thought that the soul is the form (i.e. the structure) of the body, although Aristotle does seem to have thought that it was immortal in some sense.
Philosophically speaking it's obviously possible to believe in both evolution and the soul; I should think most Christians do, including Christian philosophers such as Richard Swinburne, who wrote an entire book entitled
The Evolution of the Soul. Obviously you can believe in evolution and also in God, as well. Perhaps more surprisingly it's perfectly possible to be an atheist and still believe in souls. The philosopher John McTaggart is the best example of this; he was an atheist idealist.
I don't see how just saying the soul does not exist, because we cannot find it will cause any one to change how they reconcile the soul.
It was philosophy that tried to explain how the soul works. It is philosophy that seems to be taking the soul away.
It was philosophers who invented the idea of the soul in the first place, so I suppose they're entitled to get rid of it again. But philosophers don't deny the existence of the soul simply because they can't find it. They deny its existence (and the vast majority of them do) because the concept of the soul is incoherent, it's impossible to explain how it
could interact with the body if they're fundamentally different things, and (perhaps most important) because it just has no explanatory value. If we can explain the workings of the human mind solely in terms of the body (including the brain), as we probably can, then there's no point in imagining that some other entity is involved.