For example, lets look at language, or more specifically, bi-lingual people. Babies born and raised in a two language environment will develop two visibly distinct speech-processing regions in their brains over time. They will also be able to speak these two languages fluently, with none of those "foreign tongue" accents in either language: The baby will learn to speak both languages in ways that sound as if both were their "native" tongue.
Adults, on the other hand, will never learn to speak an additional language as well as a child would learn multiple languages from childhood. Adults brains will not develop two distinct areas, nor will the adults be able to easily switch from their original language to their second tongue without a noticeable accent in it. Clearly, the capabilities of one's consciousness and it's development, is dependent upon the states and developmental cycles of a 100% purely material biological organ: the brain.
This site explains it really well.
There is increasing evidence suggesting that there are "critical periods" for speech and language development in infants and young children. This means that the developing brain is best able to absorb a language, any language, during this period. The ability to learn a language will be more difficult, and perhaps less efficient or effective, if these critical periods are allowed to pass without early exposure to a language.
This site explains how different areas of the brain are responsible for the ability to speak and understand words.
"In particular, the PET scan ("positron emission tomography") provides a computer with the information needed to construct a three dimensional map of a persons brain including the relative activity of different areas. PET scans involve injecting someone with a radioactive glucose solution. Since active areas of the brain use more energy, and therefore more glucose, they release more radiation, which the computer translates into "warmer" colors such as yellow and red. Areas that are less active are shown with "cooler" colors such as green and blue. As by now you should expect, certain areas of the left hemisphere were more active while people were engaged in linguistic activities."
So we have seen that physical matter (your brain) is responsible for your ability to understand and communicate words. We have seen that the state or condition of that physical, material brain will affect your ability to understand language and communicate messages, as well as affect you development of those skills over time. Great. Who cares? Well, people that believe in the afterlife should care, because it says a lot about the afterlife. Or, to be more specific, the inability to go there upon your death.
In reality, all aspects of your consciousness, from communication to observation to constructing concepts to even feeling life itself, are hopelessly dependent upon your physical brain. I used communication as an example to show the hopeless dependency that consciousness has on a material existence, for demonstrating all aspects of consciousness as being dependent upon a material existence is a bit beyond the scope of this article.
Now I want to quote a bit from a wonderful book entitled "Wisdom Without Answers: A Brief Introduction to Philosophy" by Daniel Kolak and Raymond Martin.
You want you - not the atoms of your body, but you - to survive the decomposition of your body.
If you survive the decomposition of your present physical body, you must survive as something other than your present body - perhaps a soul. But what is a soul, and do you have one?
Souls are not bodies or memories or beliefs or character traits or temperamental dispositions. If souls were bodies, they would decompose when we die. If souls were memories, they would diminish as we got older. If souls were beliefs, they would change from day to day. If souls were character traits or temperamental dispositions, a lobotomy could destroy them.
Traditionally, souls are thought of as "spiritual" substances that have memories, beliefs, character traits, and so on; souls are not these phenomena but, rather, spiritual things that have them. Today we believe that it is the body - more specifically, the brain - that has memories, beliefs, character traits, and so on. We can explain the functioning of the body by appeal, ultimately, to the behavior of atoms.
What, then, is left for a soul to do?
Anyone care to answer that last question? I don't think there is any reason to even hypothesize a soul by now. It is superfluous (like God). Some theists or "after-lifers" might say that a soul is not superfluous. Some of them might say that the soul is needed to continue to the afterlife since you leave your current body upon death. It becomes your new "you" and takes over the functions that your physical body did when it was still "alive."
The theist would be presupposing that you even will, or need, to continue to consciously exist after death. Why posit a "soul" to explain how one would exist in an afterlife, when one can't even support the idea that a consciousness would need to, or should continue to exist after death in the first place? What I'm trying to say is, that science first observes phenomena and then makes conclusions. But the theist has it backwards: They would first propose a conclusion (afterlife is real), and then they claim (not observe) phenomena (a soul).
Why are humans so prone to afterlife belief? Because, like I quoted earlier from Kolak and Martin, humans don't want their atoms to survive, they want their consciousness and memories and personality to survive.
Unfortunately for after-lifers, they are down on all counts:
1. There is no evidence for the existence of an afterlife (see my last blog entry).
2. Souls are superfluous; they have nothing to do.
3. Available evidence contradicts the concept of an (unevidenced) afterlife.
4. Humans continue to physically exist after death anyway, in the form of decomposing matter.
5. Humans do not care about "physical" existence after death, but a "conscious" existence.
So, it's pretty obvious that humans are making up these afterlife ideas. They believe because they want to believe. They are afraid of losing their consciousness. I admit, I am too. But there is no "afterlife," and the only way we can extend the life of, or possibly even survive the death of our bodies, is by working to keep our consciousness operating in this life through purely material means.
Instead of making up stories about the afterlife, theists and after-lifers should ditch their superstitions and start working towards extending the lives we have here and now.