Darwin was a self-professed agnostic, freely admitting that he could find no empirical evidence that supported the belief or the existence of God. Darwin is quoted as saying, "The mystery of the beginning of all things is insoluble by us; and I for one must be content to remain an agnostic."
As such he sought, as does Darwinism and Evolution in the most widely used sense, to find and explain answers to matters of our physical existence without any theistic trappings: ergo, without God. It is widely believed that such a thing is possible, even among people of faith. Science and religion are generally accepted as two separate regions, and is often cited as governing two separate areas of existence: one physical and one spiritual. This has become a widely accepted view, even to the point of becoming a philosophical pursuit. You want cold, hard facts you pursue science: you want truth, you pursue religion or philosophy. As such, it should be no surprise that the two could be deemed as "coexisting."
And why not? If God little more than something or someone to give you comfort in your time of need, simply a savior that rescues you from a far-off eternal damnation, merely a figure in a heavenly courthouse that will one day secure your spiritual fate, why shouldn't God and Darwinism coexist? Especially if religion is simply something you practice one day a week and only a fish-like emblem you affix to your vehicle. For Darwinism and God to coexist, they would essentially have to have mutually exclusive realms of influence: and they do, correct?
Or do they?
All throughout scripture God is referred to as The Maker of Creation, Ruler of heaven and earth. He is the One who spoke everything we know, everything in the physical universe into existence. He conceived it, made it, governs it, and cares about it. He is called the Master Craftsman: the ultimate designer, engineer, construction manager and builder. He "stretched out the heavens" with His own hands. He is credited with knowing you before you were in your mother's womb, knowing the number of hairs on your head, knowing every grain of sand and every star in heaven. His presence is in the loftiest heavens and lowliest depth. There are numerous names, characteristics and attributes that relate to God, and most of them indicate that He is an omniscient, omnipotent and omnipresent God that is not only responsible for creating the physical world we know, but governs every part of it (including science).
Which obviously presents a problem.
If that is true, than most (if not all) of the truth claims of God directly contradict what Darwinism claims. Much of what we know of God and how he made the universe, ergo Creation, tells us that Natural Selection didn't have anything to do with the process. We didn't come from monkeys or apes, life didn't evolve over millions or billions of years from primordial goo. As a matter of recent conjecture, a number of experts are noting that everything from the inner complexities of biological cell structure to the vastness and magnificence of astrological bodies and how they behave belie some kind of intelligent design over some mindless "blind watchmaker." Even Darwin himself found it nearly impossible to explain certain inconsistencies with his theory and how perfectly elements of the human physiology worked. Darwin wrote, "To suppose that the eye with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest degree." So essentially you have God's claim (in scripture) that he created everything we know, including us, or Darwin's claim that it was all some unexplainable, natural, mindless process that just "happened" due to a series of cosmic accidents.
So how can we say these two things can coexist?
They can, if you dilute God's power and majesty and reduce him to an ideal or a concept. But if you take Him at His word, if you believe that what He says about Himself is true and that all Creation speaks of Him and these things are "clearly seen, " that he is Lord over both the seen and the unseen, than I am afraid you have yourself a bit of a conundrum.
I suppose it all comes down to what you really believe in.