(10) I want to revisit (1) because I fear I may have inadvertently violated one of my own rules, specifically (5e). By saying that the major reason religion is popular is that it purports to solve the problem of death (which I think everyone can agree is true), and by elsewhere implying that religion is a human invention (whose truth is debatable), I may have implied that a causal relationship exists there: that primitive man woke up 10,000 years ago and said, "Holy shit, the irrefutability of death is scary. Let's make up God!" I don't think that's how it went; to say that it was would be reaching the right conclusion for the wrong reason.
As evidenced by the tribal embrace of animism and shamanism, the idea of an afterlife, a spirit world, seems to have arisen first in human history, to be followed only later by the formalization of religious doctrines to help make sense of that spirit world (and its relationship to this one). This is an important clue to why religious believers have such a hard time entertaining the idea of a godless universe.
At first blush the idea of an afterlife seems natural and reasonable, because it lines up so cleanly with our own intuitive sense of existence. Even in day-to-day life, we feel a distinction between ourselves and our bodies. It seems self-evident that we must somehow be different from our bodies, since we feel, to a certain extent, encased inside them. We accept with barely a shrug that our bodies are made of cells and molecules and atoms, but we don't feel like we are made of anything. And it is this powerful feeling that leads to the idea of a soul, or a spirit, or a divine spark -- or, as scientists and philosophers prefer to call it, consciousness.
I am open to the possibility that consciousness really is a thing in its own right, a substance of some kind, for lack of a better word. There are plenty of unambiguously real things in nature that are unseen but whose effects can be observed -- gravity and X-rays, for instance. And if it turns out that consciousness could be found in pure form, it's not unreasonable to explore the possibility that it survives death. After all, the other substances that make up our bodies continue to exist even after we die.
For the sake of argument, let's assume that consciousness is its own thing -- that it, we, are our spirits, dwelling in our brains and driving our bodies around the way we drive our cars. This "spirit hypothesis" suggests that our motions and emotions, behaviors and thoughts, all originate from the spirit. Neuroscientists have used imaging technologies like fMRI to determine that different regions of the brain are actively involved in thinking, feeling, seeing, hearing, speaking, and moving. So this would suggest that the brain, while not the entity actually performing these tasks, is still intimately involved in them -- the brain is a conduit between the spirit and the rest of the body. It's the one physical organ that's capable of interacting directly with the spirit.
Under the spirit hypothesis, if neuroscientists say "the hippocampus is active during the formation of new long-term memories" or "the neocortex is involved in logical reasoning" or other similar claims about different regions of the brain, then this must mean that the hippocampus, neocortex, etc. are the knobs, dials, levers, and switches that the spirit manipulates in order to instruct the brain what to do. The spirit decides it wants to remember something, so it activates our hippocampus for us, and the memory is created. We can't directly observe the spirit, but we can infer its presence by watching the brain jump into action in response to its commands.
This hypothesis is not contradicted by neurological disorders like Parkinson's disease or cerebral palsy. The spirit knows what levers and switches in the brain to activate, but those levers and switches produce distorted or unintended outcomes due to the disease. The same goes for input limiters like blindness or deafness; the spirit would be capable of receiving visual or auditory stimulation, but the biological wiring required to pass that stimulation into the spirit is damaged.
However, a number of problems begin to arise with the spirit hypothesis as we delve deeper in. A major one is memory. We know memories accumulate in the brain (a process we can observe, but don't yet understand). The spirit hypothesis would suggest that memories also accumulate in the spirit; otherwise, we'd forget our entire lives the moment we die (which would make Judgment Day the celestial equivalent of Kafka's Trial). But if memories do accumulate in the spirit, why are they wiped out by Alzheimer's disease? We can see brain tissue dessicate and shrivel under the effects of Alzheimer's -- changes that would certainly explain why memories would be destroyed if they were stored only in the brain. But a fundamentally different type of substance, which is exactly what our hypothesis asserts "spirit" to be, should be totally untouched by such a merely biological problem, with its earthly viruses, cells, and molecules.
Mood disorders present another major challenge to the spirit hypothesis. If a clinically depressed man dies, is his spirit freed from the shackles of his depressed brain, or does his spirit continue to be depressed? I'm bipolar -- when I die, will my spirit continue being bipolar, or will it "revert to normal"? If depression and mania are intrinsic in the spirit, then why do so many pharmaceuticals effectively curb them? If depression and mania are external constraints imposed by an ailing brain on the spirit it contains, that indicates that much more of who we are resides in our brains than in our spirits; it violates the model proposed above in which the spirit is in control and the brain subservient to it. The machinery that supports the subjective experience of being conscious is split between the "master" and the "slave," making them peers, equal collaborators, in actual fact.
Does a mentally retarded person have a retarded spirit? Most people would say no -- their behavior is retarded because of deficiencies in the brain that limit the functions available for the spirit to manipulate. An analogy would be the difference between the same person switching from a vehicle with power steering and anti-lock brakes to one without those features. The capabilities of the driver/spirit are the same, but the quality of the driving differs due to the difference in vehicle/brain structure.
An interesting consequence of this argument is that it forces us to regard all animals as occupying the same moral plane as humans. Under the spirit hypothesis, how is a mentally retarded person different from a healthy rhinoceros? Both are alive, both are animals, but the structure of both their brains has deprived them both of the power of coherent speech. If popular spiritual morality leads us to think of a mentally retarded person as a fully healthy, intact, and capable spirit trapped inside an underpowered brain, on what basis can we not reach the same conclusion for a healthy rhinoceros? (Aside from arguing for pervasive animal rights, this also echoes the ethos of reincarnation.) If we decide to declare a priori that human brains host spirits but animal brains don't, then what are we to make of the fact that the differences between human and other brains are primarily of size, and not structure? Indeed, doesn't this violate one of the basic principles of the spirit hypothesis, that the brain's function is to enable interaction with the spirit? If the spirit hypothesis is valid, but we refuse to ascribe spirits to animals, then how do we explain the fact that animals also have brains? In that case, what are animals’ brains for?
Enough of this. I will stop pretending to advocate for the spirit hypothesis. There is plenty we don't know about how brains work, about what consciousness is, about the relationship between the two -- certainly enough that it would be churlish and closed-minded of me to flatly assert that the spirit hypothesis cannot be true. But as you can see, it has some major problems; it leads to conclusions that conflict strongly with both our scientific and intuitive understandings of the world. Fortunately, enough is known about the mind-body problem to suggest that there is a more likely explanation of consciousness than the spirit hypothesis: the computational theory of mind.
The computational theory of mind can be thought of as a sort of compromise between the spirit hypothesis and the biological realities mentioned in its preceding critique. It agrees with the spirit hypothesis that consciousness is in a fundamentally different category from other life processes. It disagrees with the spirit hypothesis that consciousness can exist without those other life processes.
To illustrate, think of walking. Don't think about any particular person walking; just think about the act of walking itself. In your mind, try to divorce the concept of "walking" from the concept of the "body" doing the walking. Is such "walking" real? Does such "walking" take place in the mundane world of cells and molecules and atoms? Of course it does. Yet no actual manifestation of "walking" can be found in the real world that does not depend on a body to do it. The same thing goes for the planet Earth, busily rotating around its axis. Rotation in general is real; the rotation of the Earth in particular is real. Yet it would occur to no one to wonder "Will the Earth's rotation continue to exist after the Earth no longer does?" Internal combustion is the same way; internal combustion exists, but specific instances of it will never be found outside of the engines that perform it. Motion and behavior are just as real as the people, planets, and engines that engage in them -- yet motion and behavior are not the same as the physical entities that engage in them, nor are their lifetimes independent of their engaging entities' lifetimes.
This almost gets at the essence of what I'm reaching for, but it still falls a tad short. A better example might be "the economy." No one has ever seen the economy, but no one doubts it exists. The economy is an epiphenomenon, a form of large-scale motion/behavior that arises spontaneously from the interaction of massive numbers of individual actors. Even though the state of the economy depends entirely on the billions of interactions among those millions of actors, we are still able to measure, monitor, and (occasionally, crudely) predict the economy's behavior based on its own characteristics, without having to examine the bank statements and credit card records of all the millions of people and businesses that constitute it. Consciousness has exactly the same relationship to the neurons in the brain. Would anyone suggest that the economy is actually a spirit that will live on after its constituents disappear?
The computational theory of mind makes two claims: first, that the purpose of the brain is to allow its host organism to make predictions about the future, and second, that the most reliable way nature has found to do that is through computation. (Humans stumbled across this principle of nature when they invented electronic digital computers.) The first claim does not necessarily mean "predicting the future" in the sense of prophecy or meteorology -- it means it in the sense of weighing behaviors against their possible outcomes. If I hear roaring on the savannah, I predict that a hunting expedition could get me eaten, so I'll spend the morning in my cave. If I tell my boss what I really think of him, I predict that my honesty could get me fired, so I'll keep my mouth shut. If I hear the sound of hundreds of small medium-density objects clanking rapidly against metal, I predict that my owner has just filled my bowl with puppy chow, so I'll get off my dog bed and go into the kitchen. Prediction is what brains are for, and computation is how the individual components of the brain have evolved to do it.
What we call "reasoning" is essentially recursive prediction: making predictions about how successful various methods of prediction will be. This self-reference is something that neuroscientistific evidence points to being a largely unintended consequence of increased brain size. This is why humans speak, write novels, produce films and television shows, exchange currency for goods and services, compose poetry, perform music, dance, and do calculus, while animals don't.
I was going to include "wage war" in that list, but strangely enough, it turns out that hive-based insects are our only cousins in the animal kingdom who do this as well. (That should show you where war falls on the ranked list of human achievements, no matter what Patton might have said.)