Since Evolution Theory has the full support of the scientific community in our time, it has heavily influenced Christianity. Evolution, of course, is the idea that all living creatures are the result of divergent changes over time, and that ultimately all living creatures essentially have a single common ancestor. And this single common ancestor must have formed from the combination of various non-living chemicals. But this whole process of Evolution must have thus far taken billions of years. And it is a process which is entirely naturalistic. That is, it does not require any input from God.
Since Evolution Theory has become such a fundamental belief system in our society, Christians can't help but be challenged by it. Whenever a person's beliefs are opposed by a conflicting idea, or by what appears to be evidence to the contrary, we all try in some way (probably without exception) to explain the conflict. Some will give their own belief system the benefit of the doubt, and may seek to find fault in the opposition. Others will accommodate the conflict by sort of merging the two belief systems. Christians have done both in regard to Evolution. Many Christians remain unconvinced that the Earth is billions of years old, looking at things like the rate of continent and coastline erosion, or the salinity of the oceans. Others feel that the arguments are strong for an old Earth. How do these people reconcile the conflict between an old Earth and the Bible's seven days of creation? For them, the seven days are not seven literal 24-hour days. Rather, each of these days represent periods of time which could have lasted millions of years. Some Christians find the fossil record compelling evidence for an old Earth, and see in them evidence that some creatures did not exist until later in the Earth's history. To accommodate this into the Christian belief system, some believe that God actually used the process of Evolution as the means by which He created all things. That is, He simply set up the initial conditions for it and left it to progress naturally. Alternatively, some believe that God has intervened from time to time, creating new species out of nothing at various points in history. These are some views which may be held by sincere and genuine Christians who are simply trying to reconcile modern science with their belief in the Bible.
My own view is to take the Bible as speaking of seven literal days. The Bible considers Adam to have been a literal person, in the genealogies and in places like Romans 5 for example. If Adam was a literal person and his life began on the sixth day of creation, and we continue to hear the story of his life after the seventh day, then there's little more evidence I need, personally, to understand that the writer of Genesis intends for us to understand the seven days as literal 24-hour days, for how could Adam survive a "million-year day"? Furthermore, the Genesis account says that Adam was created before Eve, which would be impossible for any evolutionary explanation. But also, I think that it is important to understand that man is distinct from animals. These theories which suggest that God allowed man to evolve from a pre-existing creature miss the significance of the Biblical idea that man was created in God's image. In Genesis 2, God gave man dominion and authority over all the living creatures. This authority is part or what it means to be made in God's image. God, who has authority over all things, has given us some authority over His creation. The role that we play in God's kingdom is to be 'images' of the king; not only in ruling over creation, but in many other ways we are to imitate God. Of course we do a poor job of it now because we are a fallen race; but this is God's intention for mankind nonetheless. We were made to oversee God's creation, so it doesn't make sense to me that man would have evolved over billions of years from a pre-existing creature. If Adam were descended from line of creatures, he would have had a father; and wouldn't that father have been so close to human that Adam could hardly have been called the first man? It doesn't make sense, but it also denies the plain Text which tells us:
the LORD God formed the man of dust from the ground and breathed into his nostrils the breath of life, and the man became a living creature. (Genesis 2:7)
It was from the dust that Adam was formed by a direct act of God, and it was when He breathed life into Adam that he became a living creature. This verse poses a real problem for the idea that man may have evolved from a pre-existing creature, even if by God's own providence over Evolution. That is to say, even if this story were allegorical, what would this mean that "Adam became a living creature"?
Understanding the Bible isn't straight forward. We aren't always supposed to take everything we read literally, since the Bible is full of poetry and other genres. And while we should carefully judge our experiences and the way we interpret the world around us in light of Scripture, we sometimes have to work the other way too, and reason that our interpretation of Scripture may be wrong when the reality of human existence contradicts what we think we've understood from the Bible. But the Lord does want to engage our minds and have us think carefully through these things; to figure out what position to take, and to sort though the conflicts that we come across. This is why He made us with an intellect. It's part of growing and maturing as a Christian. We have to be very careful that we are completely honest with ourselves, and that the view we hold is the result of a genuine effort to understand God's Word.
What is man that you are mindful of him, and the son of man that you care for him? You have given him dominion over the works of your hands; you have put all things under his feet (Psalm 8:4,6)