Wednesday, September 14, 2011

The Death of the Soul

Christians believe that every human has a soul: an immortal spiritual entity—one with thoughts, emotions, memories and desires—that controls the brain and body, and will go to heaven or hell upon physical death. In a nutshell, most Christians think that you are your soul. Below I will lay out the reasons why it's unlikely that this is so. (Along the way I'll be borrowing heavily from Ebon Musings' absolutely fantastic essay "A Ghost in the Machine.")

In Philosophy
The concept of the soul is already at a disadvantage from a philosophical perspective before the debate even begins, simply because dualism is more complicated than its alternative. It has more components than monism, and thus (all else being equal) is inferior as an explanation. There is no reason to posit the existence of some ghostly supernatural entity unless doing so offers more explanatory power. The burden of proof is ultimately on people who believe in the soul to prove that the soul exists, not on nonbelievers to prove that it doesn't.

So let's start with a basic philosophical and scientific question: how is it, exactly, that the spiritual interacts with the physical? The natural world is made up of matter and energy, while spiritual things are composed of... well, that's actually not at all clear. In any case, physical processes like firing neurons can only occur as a result of physical forces exerted according to physical laws. For non-physical souls to exert force on a physical object would be to constantly violate the fundamental laws of the universe. To say that miracles are constantly occurring in the heads of every human on the planet is to make a claim that is extraordinary in the highest degree, with no evidence whatsoever to back it up.

In Biology
The problems for the soul doctrine start right from the moment of conception. As it turns out, a single human zygote sometimes splits in two to create identical twins. In other cases, two human zygotes can fuse to create a single person, known as a chimera. So, does one of each pair of identical twins then lack a soul? Does a chimera go through life with two souls that battle each other for control of the mind and body? I suppose God could jump in and add a soul if a zygote splits, or only put a soul into one of the zygotes that will fuse into a chimera. But what a needlessly convoluted system this would be, when it's so much simpler to just relent and admit that no souls are needed at all.

Another practical problem becomes apparent when looking at the issue from an evolutionary perspective: when, precisely, did we get souls? Over the past few billion years, we've made a smooth transition from self-replicating molecule to intelligent, sentient human. Did we have souls all along, or did we acquire them along the way? What made God shove a soul into that particular member of Homo sapiens (or whatever creature it was) and not its relatives—and what exactly did this addition grant them that they didn't already have? From a biological standpoint, the addition of a soul seems both superfluous and arbitrary.

In the Brain
The most serious problems with the soul are revealed when one closely studies the brain itself. For instance, one interesting consequence of neuroscience is that we can monitor a person's brain activity and predict with 60% accuracy which of two choices they will make—10 seconds before they are conscious of having made a decision. The implications are enormous: rather than a soul signaling its choice to the brain, it appears that these choices are dictated by preceding brain activity. As our technology continues to improve, our prediction intervals and accuracy will doubtless increase, demonstrating this with even greater clarity.

Mental disorders are yet another powerful indicator that a person's identity does not reside in some ethereal spirit:
  • If your hippocampus is damaged, you may get anterograde amnesia. You would be incapable of forming new memories; your identity would be forever remain just as it was at the time of the damage.
  • A stroke in your right brain hemisphere could not only paralyze the left half of your body, but also cause you to deny your paralysis and even invent sincerely believed excuses for why you won't move.
  • Damaging your ventromedial prefrontal cortex (as in the famous case of Phineas Gage) may impair your ability to plan and make decisions, making you go from kind, polite and responsible to grouchy, crass and lazy.
  • If you've inherited a disorder called frontotemporal dementia, your entire worldview—including your politics and even your religion—might be completely altered.
  • If your right hemisphere is incapacitated, you may become emotionally dead; one patient who'd been close with his sister simply didn't care when he was told that her leukemia had relapsed.
  • A brain tumor pressing against the orbitofrontal cortex could cause you to become sexually promiscuous or even a pedophile.
  • Damage to the frontal lobes could give you environmental dependency syndrome, causing you to automatically make use of any object (e.g. write with a pen or comb with a brush) placed in front of you.
  • If your anterior cingulate cortex is damaged, you might develop akinetic mutism, leaving you fully conscious but completely removing your will to move or speak.
If our identity is contained within the soul, it seems absurd that a brain disorder can utterly erase or even rewrite one's personality, beliefs, memories and free will. It's hard to see how Christians can possibly hope to explain this, and yet I still haven't gotten to the most damning evidence against the soul: the split brainOne effective treatment for epilepsy in the mid-1900s, used only in extreme cases, was to sever the corpus callosum, a small band of tissue connecting the two hemispheres of the brain. Using specially designed tests, scientists found that one hemisphere can know things that the other doesn't, and the two hemispheres can respond to stimuli independently of one another.

But that's only the beginning. In one case, a man's left hemisphere expressed a desire to become a draftsman, while the right hemisphere's ideal job was racecar driving. In another instance, a woman's left hemisphere was suicidal and repeatedly tried to use her right hand to strangle herself to death. In still another, one hemisphere believed in God, while the other did not. What does one call this, if not two distinct identities occupying one head? Do these people have one soul or two? And if only one, where would the theist/atheist go upon death?

Yeah, we're pretty sure it doesn't
work this way.
There are a couple of frameworks that theists may use to explain these phenomena. Maybe the brain is the medium through which the soul interacts with the world, and if that medium is broken, the soul can't get its messages through. But this would imply that deep down every mentally impaired person is lucid, trapped, desperately trying to communicate with the outside world. This is not only ridiculous, but demonstrably false: people who recover from mental illnesses report no such struggles.

Maybe the brain is the self, but its contents are later transferred to a spiritual body upon death. But why would God allow the self to be become utterly compromised so easily? Experiments have shown evidence that certain pathways in the brain are what cause religious experiences of all kinds. So why not just leave souls in the spiritual realm, where their experiences can't be impaired by brain damage or counterfeited by false religions? Furthermore, if a brain is damaged to the point where the selves before and after the damage are mutually unrecognizable, which self is allowed to move on to an afterlife, and on what grounds is the other excluded?

I've shown here that the concept of the soul is flawed in numerous ways. It not only adds needless complexity to our understanding of the mind, but also conflicts deeply with biology, neuroscience, and even the fundamental laws of physics. Most brain scientists and philosophers of mind long ago gave up on the sort of dualism espoused by Christians. It's high time for the rest of the world to follow their lead.

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