People really like the concept of the soul. It is often the last religious relic that modern, non-religious people give up. Atheists often simply dismiss the soul as not worth considering, but I think it is worth considering its varying definitions and its psychological appeal. One goal of my Natural Liberation Philosophy is to align my thoughts as much as possible with Nature. This often requires more careful thinking than that leading to simple Yes or No type answers. The true answer always seems to be, it's complicated. This short essay is an introduction to these ideas and a basis for further discussion.
The basic idea of the soul arose in pre-historic times. Once history starts (with the invention of writing) we start to see ideas mentioned that correspond in some way to our more modern ideas of the soul. Animism, the belief that all things, including mountains, rivers, and trees, have a spirit, is likely to have pre-dated civilization, much less history. As religions developed this basic idea (dualism, the idea that a spirit is necessary to animate a material body) was refined.
Ghosts are associated closely with the ideas of soul and spirit. Some people still believe in ghosts, and some honest research still goes into trying to "find" ghosts, but for the most part the concept is now maintained by horror movies rather than religious belief. Reports of ghosts doubtless are based on the human mind's ability to remember the dead, including in dreams and in waking dreams. Dismissing our modern concept of ghosts simply sharpens the religious definitions of soul.
Like a ghost, a soul is supposed to live after death. The ancient Egyptian view of the soul was quite complex. In Hinduism and Buddhism the soul also exists in a complex state before any particular life, and goes from a dead person or animal into a a new baby person (transmigration or reincarnation). In Christianity, while there are differences of opinion within sects, for the most part humans at conception or birth are given a newly-manufactured soul, pre-corrupted with original sin. In both cases the soul carries, or remembers, the good and bad deeds of a person. In is sort of a sin accounting sheet.
The soul is associated with life (as opposed to dead corpses) and in particular with the mind and consciousness. The mind and consciousness are real enough. However, every indication are that they start functioning around the time of birth and cease functioning at death. The concept of soul extends that functioning to before and after an individual's life. This seems to be mostly a function of fear of death. People fear their own deaths, they mourn the death of people they love, and are frightened by the deaths even of people they do not love. It is also a result of valuing the present over the past.
That type of soul, the kind that is conscious and thinks and holds memories and lives after death, is simply imaginary. If such a soul were real we would not need so many nerve cells in our brains to function, and lesions in the brain would have no effect on our behavior. The body animates itself, when it is healthy.
Another aspect of the soul concept that is appealing to many people is its cleanliness, its theorized inability to be stained by the less pleasant facts of life. The soul does not urinate, defecate, or have bad breath. It appeals to people who fancy that cleanliness is next to godliness. This also pairs up well with many people's desire to think of themselves as "spiritual" rather than greedy and materialistic, even when they are not otherwise religious. It is strange that the opposite of greedy is considered by people to be eternal life, rather than mortality.
But what if we do go looking for eternity, or at least something that does last longer than a particular human brain? There are some soul-like substances worthy of discussion. The main ones are the genes, which provide biological continuity, and culture, which provides a continuity beyond our animal existence.
The one thing intrinsic in us that definitely exists prior to conception and that animates human life is our biological ancestry. I'll use DNA here not just to mean the molecules that code our genes, but the complex fabric of life, including the non-DNA parts of the ovum that contribute to the development of fetuses.
DNA is shuffled quite effectively each time a new human is conceived, so unless a community is highly inbred an individual is not identical to the father or mother, and is not likely to be identical to any particular ancestor. Yet most DNA is shared with all humans, and no individual has any unique DNA unless they have a new mutation or are the last of some line, usually meaning they have a life-threating mutation inherited from an ancestor.
Our DNA is a record of our past, of over a billion years of choices and interactions with the the rest of nature. It is the soul of each new human. There is no guarantee that an individual will reproduce, but our DNA is a result of a common ancestry we share with all humans. Unless all humans die, all the DNA in you will be passed on to the next generation even if you don't reproduce personally. Whether this is as reassuring to you as the false idea of a ghost-soul that lives after your death depends on your attitude. Life goes on, but not your particular individual life. That said, I don't think DNA, in itself, is conscious. It is the blueprint for the body, which is conscious.
Culture goes on too, and it existed and developed for hundreds of thousands of years before your birth. Culture is more flexible and tolerant than DNA; it is more capable of experimentation. Culture includes art and ethics, language and technology, religious and social beliefs. Without it, you might survive, but you would be very animal like. You would not be able to think in the sense that people who know a language think.
Language, in particular, is a soul-like substance. It penetrates from the adults caring for a baby and wells up within, naming the things of the world and describing their relationships. Language has been described by philosophers and poets alike as a living thing, a vast edifice of spirit that possesses and shapes us throughout our lifetimes.
When someone argues that humans have souls, I want to know exactly how soul is defined by that person. Since most of the religious definitions of soul make no sense or are clearly make believe, I prefer to avoid using the term except in a poetic sense. I am more interested in mind, intelligence, empathy, and consciousness, which while also sometimes vague or difficult to define, clearly have their role in our natural reality.
See also: God, a Confusing Concept
For a rundown of how many religions define the soul, See Soul at Wikipedia.