One of the things that seems to really unsettle people about the idea of evolution is that they imagine is sidelines God's creative power. Did God create the world directly, people ask, or did He simply stand aside and guide some process of evolution which did it?
One problem here is that we tend to fall into thinking of God as rather like us, and God's creation as rather like our "creations" of art or engineering. As creatures within creation, it's reasonable to ask "Did you create that or did someone else or did it just happen naturally?" If I paint a picture of a sunset, one can refer to the paining as my "creation", but the horizon and the sunset are clearly not my creation. They "just happened naturally". If I were to set up a giant frame through which you could see a distant vista and say, "Look what I made!" you would reasonably reply, "You didn't make that. That's nature."
However, God is not a creature within creation. God is the creator of all of creation. He holds it in existence by His constant act of the will. The natural laws that we observe are the product of His ordering will. God is the answer to the question, "Why does anything exist?"
As such, it makes no sense to say that if something happens "naturally" that it is not God's creation. Imagining again that giant frame set up so that one could, through it, view some distant vista, one would not tell God, "Oh, you didn't make that, that's just nature," since, of course, nature is God's creation.
Even our knowledge that there are natural processes that shape the things around us does not change this. We know, for instance, that a mountain is the result of tectonic pressures that push up the rocks of the earth, and erosion that wears them down into their current shapes. Glaciers, wind, water and plants leave their marks upon the landscape. But this doesn't make them less God's creation, because all of these, and the ways that they act, are in turn part of God's creation.
And yet, somehow the idea of biological evolution throws many people off. If humans are the result of some long ancestry of proto humans, if we somehow share common ancestors millions of years ago with the great apes, how can we be really made in the image of God? How can we really have a divinely created soul? Doesn't it take away from the belief in God's creation to hold that we were created by a natural process?
I think the scale of the question tends to throw us off. After all, each one of us was created by a natural process. Via a natural process, a man and a woman have sexual intercourse. The man's sperm comes in contact with the woman's egg. The egg is fertilized. DNA from the two parents joins to form a unique, new set of DNA and that first cell of that new human being splits and then splits again. There is a continuity of being between me and the joining of an egg and sperm 35 years ago. I was formed by this natural process, a process which the biological sciences have managed to come to understand in great detail over the last few centuries.
And yet, we don't consider God to be "sidelined" by the fact that his creatures can, through their act of intercourse, cooperate in the creation of a new human being. That we have a detailed biological understanding of how I descended from my parents does not mean that God did not create me, that I do not have a soul, or that I am somehow "only a natural process" and not a product of God's will.
We accept, as Catholics, both that a new human being is the product of the natural process of conception, and also that a new human being is the creation of God. We accept that the natural process in which the bodies of the parents take part is also a part of God's creative power. We accept both that we can have a complete biological understanding of the natural process of conception, and also that that biological understanding does not mean that humans are nothing more than cells -- that explaining the biological does not mean explaining the whole of reality.
What we need to remember, then, is that evolution is nothing more than the repetition of that process (reproduction) over many individual over a great deal of time. If my natural descent from my parents is no threat to our belief, then our natural descent with modifications due to variation and selection over thousands and millions of generations can be no more of a threat to our belief in God's creative power and providence.