As I read The Demon-Haunted World, by Carl Sagan, I am overwhelmed by the clarity with which he tackles difficult and sensitive issues. One of his most compelling passages relates to the "soul," which both Sagan and I consider a delusion.
Nearly every religion asserts that human beings possess a soul or immaterial eternal essence, a "ghost in the machine" that animates our flesh. However, this extraordinary assertion is backed by essentially no hard, scientific evidence. What causes people to believe in a soul for which there is no hard, scientific evidence? I propose that there are two predominant reasons:
- Belief is prescribed by faith. For many people, religion's claims are assumed to be true, even if no supporting scientific evidence exists.
- Belief provides substantial comfort. Many people fear the end of their own existence (and the existences of their family and friends). The notion that death is the ultimate end frightens many, and belief in an immortal soul is comforting, whether that belief is supported by scientific evidence or not.
Here's Sagan's take:
Thus, the idea of a spiritual part of our nature that survives death, the notion of an afterlife, ought to be easy for religions and nations to sell. This is not an issue on which we might anticipate widespread skepticism. People will want to believe it, even if the evidence is meager to nil. True, brain lesions can make us lose major segments of our memory, or convert us from manic to placid, or vice versa; and changes in brain chemistry can convince us there's a massive conspiracy against us, or make us think we hear the Voice of God. But as compelling testimony as this provides that our personality, character, memory--if you will, soul--resides in the matter of the brain, it is easy not to focus on it, to find ways to evade the weight of the evidence.
Additionally, consider the famous case of Phineas P. Gage. Gage worked in railroad construction. As a result of a freak accident, Gage suffered an atypical traumatic brain injury that wrought severe damage to parts of his brain's frontal lobes. Astonishingly, Gage emerged from the incident just fine in terms of memory, motor skills, language skills, etc. However, of all things, his personality had changed--in a most dramatic fashion.
The following quote offers details as provided by Gage's physician:
[Gage was] fitful, irreverent, indulging at times in the grossest profanity (which was not previously his custom), manifesting but little deference for his fellows, impatient of restraint or advice when it conflicts with his desires, at times pertinaciously obstinate, yet capricious and vacillating, devising many plans of future operations, which are no sooner arranged than they are abandoned in turn for others appearing more feasible. A child in his intellectual capacity and manifestations, he has the animal passions of a strong man. Previous to his injury, although untrained in the schools, he possessed a well-balanced mind, and was looked upon by those who knew him as a shrewd, smart businessman, very energetic and persistent in executing all his plans of operation. In this regard, his mind was radically changed, so decidedly that his friends and acquaintances said he was 'no longer Gage.'"
As neatly summarized at Wikipedia, "According to Gage's physician--whereas previously he had been hard-working, responsible and popular with the men in his charge, his personality seemed to have been radically altered after the accident."
Through the Gage case and myriad others, science makes it quite clear that the brain is the place in which one's personality, character and memory are stored. In regard to the "mind" vs. "matter" issue, only one conclusion can be drawn from the available scientific evidence: "Mind" is merely a self-organized emergent property of matter. In other words, the product (consciousness) is greater than the sum of its parts (billions of neurons).
Three excellent references on this point are:
- Astonishing Hypothesis: The Scientific Search for the Soul, by Francis Crick. The author is a Nobel Prize-winning biochemist.
- The Quest for Consciousness, by Christof Koch. The author is a California Institute of Technology neuroscientist.
- The Blank Slate: The Modern Denial of Human Nature, by Steven Pinker. The author is a Harvard University professor.
If personality, character and memory all are explicable in terms of the brain, then what purpose would a soul have, anyway? Moreover, even if a soul existed, how could one possibly consider it an "afterlife" if personality, memory, etc., do not make the journey, too? After all, upon death, the brain quickly dies (more quickly than most organs, in fact), all its properties and functions rotting along with it. If there are ghosts, they don't remember a thing and lack a personality.
For those who persist in believing in the soul, I pose these closing questions:
- How does the immaterial (soul) interact with the material (flesh)? Is there any precedent for the immaterial interacting with the material? What is the process by which this occurs (with as much specificity as possible)?
- Is the soul falsifiable? If a notion is not falsifiable, then it's pretty much worthless, at least scientifically speaking. What is the process by which the soul claim could be falsified (with as much specificity as possible)?
Extraordinary claims require extraordinary evidence. This evidence must be scientific as opposed to evidence of the soft variety, such as anecdotes, personal testimony and feelings. The "feeling" that one has a soul does not constitute anything even approaching convincing evidence. Innumerable children "feel" the presence of Santa Claus on Christmas Eve night, in a way very similar to how most humans "feel" as though a ghostly soul inhabits our flesh; (neurons really are the master illusionists ever to exist).
The soul claim is truly extraordinary, on multiple levels.
I anxiously await a mere whisper of hard, scientific evidence for the soul assertion, as do my fellows in reason.
 Sagan, Carl. The Demon-Haunted World: Science as a Candle in the Dark. New York: Ballantine Books, 1996.
 J. M. Harlow, 1868 (Publications of the Massachusetts Medical Society 2: pp. 339-340),
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