From the blog Always Have a Reason, a case against the idea that Christians can embrace a materialist conception of humanity.
Problem 1: a concept of the self that persists through the passage of time:
How do we maintain identity through time? Here, the problem must be answered by all materialists, not just Christian materialists.
The problem is, of course, that our bodies don’t maintain physical identity. We are continually replacing the physical parts of our body over time. Now, I am hesitant to make the oft-repeated claim that our entire bodies are replaced every so many years, as I have been unable to find any research confirming it. However, it simply is the case that large portions of our body are replaced. Given this fact, how do we maintain identity? What is it that keeps us the same person over time?
Another major problem is this: to which part of our body are we identical? Or, to put it another way, which parts of our body do we need to keep in order to be the same person? Here we can appeal to a thought experiment. A mad scientist has us captured and he wants to see how long we can maintain identity. Slowly, he replaces each part of our body with a new one with the exact same DNA, structure, etc. As he replaces these parts, he discards the old ones and destroys them. He starts with the legs. Then he moves to the midsection, replacing one organ at a time. Then the heart, the arms, the ears, the eyes. When he gets to the brain, he goes through and replaces only single neurons at a time.
The question is pretty obvious: When do we stop being the same person? The materialist simply has to admit that we are our bodies (for what else could we be?). But given that fact, to which part are we identical? The brain? If so, at one point in the experiment do we cease to exist? 51% of our brain is gone? 70%? All but one neuron? So is our identity grounded in that one neuron? If so, which one? Or is it just grounded in having any one neuron as the same? If so, how?
Problem 2: materialism cannot make sense of the bodily resurrection:
Central to the Christian hope is the hope for a future resurrection. The question which must be asked is this: Is this hope grounded in reality?
Suppose materialism were true. If that is the case, then humans are identical with their bodies in some fashion. I am intentionally vague here because I admit I’m not convinced as to how identity works within a Christian view of materialism (see above). If this were the case, then when we die and our material body decomposes, it may go on to become all sorts of different things, which themselves later pass away (plants may grow from the nutrients broken down from the body; then those plants may be harvested and eaten by other humans/animals/etc, which then die and are broken down, etc.). In the resurrection, then, God creates our body anew, complete–I assume–with our memories, experiences, etc. built in (perhaps they are simply functions of our brain, which God recreated perfectly, which thus contains our experiences).
Is there actual hope on this scenario?
Suppose the mad scientist were to come and kidnap you. He gleefully announces that he is going to use you for excruciatingly painful experiments which will take place over several years until you die. But, do not worry, because once you die, he is going to create a new body which is an exactly perfect copy of you, which will of course have all your experiences (minus this torturous one) and memories in place, and then he is going to give you billions of dollars.* Would you be comforted by this scenario? After all, you’re not going to remember the pain and you are going to come out the other end extremely rich!
Well there is a problem: the new body is not you. It is just a copy. For any materialist, this is problematic. We seem to know that identity transcends the body. But let us not delve into that difficulty right now. Instead, we will focus on Christian materialism. Now, it seems to me that this problem is almost the same for the Christian materialist with the Resurrection. After all, we are going to die. But we are told, don’t worry, we will be raised bodily by God! But whose body is going to be raised? How will God gather the material from our body (and at which time of our body–see above) in order to recreate us? And will not this body purely be a copy, rather than actually us?
There is a real disconnect here. Christian materialism cannot offer us the hope of the resurrection, without which our faith is worthless (1 Corinthians 15). Instead, it offers us the hope for our future copies, which will themselves have our memories and experiences, but will not be us. Our bodies will die and distribute throughout various portions of the world (even the universe–who knows if an asteroid might hit and distribute the molecules which made up our body elsewhere?). Then God will create us again in some fashion, and that body will live on in the Kingdom. But that body is not us. It will be a new body. This isn’t begging the question, it is merely stating a fact. The body that will be raised is not the body I have now. Thus, if I am my body, I am not raised.
And I would add to that additional problems with generic materialism, like first-person consciousness, freedom of the will, rationality, and so on. It’s just not a sound view.
I remember attending a philosophy of religion conference at Wheaton College a long time back, where the main speaker was Christian materialist Peter Van Inwagen. Both of these objections were raised against him, and neither objection was adequately responded to, in my opinion. In contrast, the orthodox view (body and soul dualism) holds up very well. The biggest problem with the dualist view (my view) is how do the body and soul/mind interact. But I think that problem is much smaller than the problems that J.W. raised above.