It seems like Christianity should be compatible with evolutionary theory — after all, many churches (including the Catholic Church) and many Christians accept evolution as scientifically accurate. In fact many of the scientists who study evolution label themselves as Christians. Fundamentalists who argue against such accommodation, though, insist that belief in evolution undermines the Christian faith. Do they have a point and if so, what in Christianity is contradicted by evolution?
Sin and Faith
The central message of Christianity is that Jesus' death and resurrection pays for our sins — we deserve death and eternal punishment, but Jesus paid the price for us. To paraphrase Paul: without that, the Christian faith is in vain. Without these sins, there would be no need for Jesus to be punished and killed. The question then becomes: is this notion of sin tenable from a naturalistic perspective? We have to approach it from a naturalistic perspective because our central question involves evolution, and the process of evolution is supposed to describe the development of our species in a purely naturalistic manner.
If the evolutionary account of human origins is true, then there was certainly no literal Fall from Grace — no Adam and Eve disobeying the Christian God and no Original Sin. But without Original Sin and expulsion from the Garden of Eden, then there is no reason to think that anything called "sin" (which is supposed to be disobedience to God) suddenly entered the world. If sin instead "evolved" into our ancestors through the natural development which God set into motion, why would God hold us accountable? A naturalistic development of sin should mean that insofar as we are "naturally" sinners, we simply are what our creator caused us to evolve into being.
Literalism vs. Metaphors
All of this is obviously true if the Bible is read literally as the fundamentalists do, but what if the Bible is read metaphorically or allegorically? The problem is that it's difficult to argue that a metaphorical Fall required a literal death and resurrection. One might argue for a metaphorical death and resurrection, but few if any Christians believe in that and doing so would mean rejecting some very important, orthodox facets of Christian theology.
Some might argue that "sin" should be read as simply "transgressing moral codes" and "original sin" is really the "original self-awareness" of moral codes, but whose moral codes? If we are the creators of the moral codes, then what we have is the assertion that God needed Jesus to die because we have trouble following rules we create for ourselves. Not only doesn't that make much sense, but it doesn't look much like traditional Christianity anymore.
Within the framework of evolution, sin does not appear to have any tangible, real existence. We are supposed to have sin, but did Neanderthals? Homo Habilis? Homo Erectus? Is is possible to logically argue that this "sin" was dependent upon some specific piece of genetic code which evolved into our species? There is evidence that other primates, like chimpanzees, not only have rudimentary rules within their groups but also an awareness of when they are and are not following them. Are chimps sinning? Did Jesus die for them, too? Should we be sending missionaries to them in zoos and jungles?
Some might also argue that "sin" is still "disobedience to God," but only where it concerns those moral rules God has given us. This eliminates the Fall of Original Disobedience, but it still has problems. For one thing, these same people are unlikely to argue that the moral rules from God have reached us unadulterated by human interests — so the situation begins to look a lot like the previous. For another, it would be hard to argue that disobeying this limited set of rules would justify a literal death and resurrection. Again.
None of this can be easily argued. Sin, our alleged disobedience to God, appears to be nothing except one more religious concept created by some human beings and imposed upon other human beings. That, however, would mean that Jesus died for nothing, and no devout Christian can really accept that.
Souls & Evolution
Jesus was supposed to have 'saved' us by dying for our sins, but it is not our physical bodies which have been saved — instead, it is our eternal souls. If we don't have souls, then it is unlikely that Jesus' alleged sacrifice had any real significance.
But how can the existence of a soul be reconciled with evolution? I do not believe in souls, but I can at least comprehend how they might have been brought into existence along with a "special creation" of our species. Where could souls come into play during the evolution of homo sapiens out of earlier hominids and primates? Did Cro Magnons have souls? Neanderthals? Homo Erectus? Why or why not?
What would make one hominid species so special that it would have a soul and not another hominid species? If they did have souls, were they saved without Jesus? If they weren't saved, then the Christian God is cruel and capricious. If they were saved without Jesus, then there's no reason for me to need Jesus. But if we are so special and are the only hominids to have, what on earth was the point of those earlier species of hominids? Why did they struggle, suffer, and die?
Why, in fact, was there a process of evolution at all? Why all the time, death, and suffering over millions of years of so many species now extinct? Was it just to create us? The entire Neanderthal line apparently developed and ended without direct impact upon our eventual development — and for what?
Christianity actually seems to make more sense within the framework of a cosmology that reads Genesis literally in at least some ways, particularly when it comes to the special origins of humanity. One word of caution: saying "God works in mysterious ways" is an essentially meaningless answer to all of this. All it serves to state is that "I don't know either, but I still believe."