Why evolution and much of science require faith...

...because humans suffer from a "poverty of imagination."

Although it may be a faith in reason, but then so is much of Christian faith a "faith in reason."

Michael Denton observes in "Evolution: A Theory in Crisis":

One of the strategems adopted by Darwin in the Origin and used by many evolutionary biologists since, when faced with the difficulty of envisaging transitional forms, is to allude to the poverty of human imagination and to the very surprising and curious adaptations and behaviour pattersn many organisms exhibit - the implications and being that had we not known of such bizarre adaptations we would never have believed them possible.

Id. at p. 227 - 228.

Interestingly, St. Augustine noted that this limitation - and its attendant consequences - are a feature of the human mind which understands by taking what it has experience of and adding or subtracting those things about which it also has experience. In "On the Trinity," Augustine wrote:

10, 17. But then if we only remember what we have sensed, and only think what we have remembered, how is it that we often think false things though we do not of course remember falsely what we have sensed?23 It must be that the will, which I have been at pains to present to the best of my ability as coupler and separator of this kind of thing, it must be that the will leads the thinking attention where it pleases through the stores of memory in order to be formed, and prompts it to take something from here out of the things we remember, something else from there, in order to think things we do not remember. All these assembled in one sight make something that is called false because it is not to be found outside in the nature of bodily things, or because it does not seem to have been derived from memory, since we do not remember ever having sensed such a thing. Has anyone ever seen a black swan? So no one remembers one. But is there anyone who cannot think of one? It is easy enough to suffuse that shape which we know from seeing it with the color black which we have seen no less in other bodies, and because we have sensed them both we remember them both. Nor do I remember a four-footed bird, because I have never seen one;24 but it is very easy for me to look at such a fancy when to some winged shape I have seen I add two more feet of a sort that I have also seen. So when we think of two things in combination which we remember having sensed one by one, we appear to think of something which we do not remember, though we do it under the limitations set by memory, from which we take all the things that we put together in many and various ways as we will.

Again, we cannot think of bodies of a size we have never seen without the aid of memory. We can extend the masses of any bodies when we think of them to the maximum extent of space that our gaze is accustomed to range over through the magnitude of the universe. Reason can go further, but fancy does not follow, inasmuch as reason declares an infinity of number, and this no thinking about bodily things can grasp with inner sight. The same reason teaches that even the smallest corpuscles can be divided to infinity; but when we reach the limits of minuteness or fineness that we remember having seen, we cannot now gaze on any slighter or minuter fancies, though reason does not stop proceeding to divide. So we do not think of any bodily things except what we remember or unless they are composed out of what we remember.

Saint Augustine of Hippo; John E. Rotelle; Edmund Hill (2011-01-23). The Trinity (The Works of Saint Augustine) (pp. 319-320). New City Press. Kindle Edition.

Reason can tell us that something exist in some sense - the concept of infinity, for example - but try as we might we are not going to be able to "imagine" - picture, understand, grasp - infinity because we don't have an experience of infinity, we only have an experience of finite things, and add as many finite things as you want, you still only have finity.

On the other hand, even Augustine could imagine a "black swan" because he had an experience of "swans" and "black" and by compounding the two ideas, he came up with an image  of a "black swan."

Evolution, black holes and the experience of travelling at the speed of light, but also God's infinity, omniscience and simplicity, are places where are reason can travel further than our imagination.