Doubts about Darwinism

From G.K. Chesterton:

It is very far from obvious that the first rudimentary suggestion of a horn, the first faint thickening which might lead through countless generations to the growth of a horn, would be of any particular use as a horn. And we must suppose, on the Darwinian hypothesis, that the hornless animal reached his horn through unthinkable gradations of what were, for all practical purposes, hornless animal. Why should one rhinoceros be so benevolent a futurist as to start an improvement that could only help some much later rhinoceros to survive? And why on earth should its mere foreshadowing help the earlier rhinoceros to survive? This thesis can only explain variations when they discreetly refrain from varying very much. To the real riddles that arrest the eye, it has no answer that can satisfy the intelligence. For any child or man with his eyes open, I imagine, there is no creature that really calls for an answer, like a living riddle, so clearly as the bat. But if you will call up the Darwinian vision, of thousands of intermediary creatures with webbed feet that are not yet wings, their survival will seem incredible. A mouse can run, and survive; and a flitter-mouse can fly, and survive. But a creature that cannot yet fly, and can no longer run, ought obviously to have perished, by the very Darwinian doctrine which has to assume that he survived.