I will answer this question with Kant's own words taken from (my personal favorite of his works) The Critique of the Power of Judgment. Specifically, I will be citing the Cambridge University Press 2nd Edition, edited by Paul Guyer and translated by Paul Guyer and Eric Matthews. Please decide for yourself what you think Kant would think of Darwinian evolution.
"The agreement of so many genera of animals in a certain common schema, which seems to lie at the basis not only of their skeletal structure but also of the arrangement of their other parts, and by which an admirable simplicity of basic design has been able to produce such a great variety of species by the shortening of one part and the elongation of another, by the involution of this part and the evolution of another, allows the mind at least a weak ray of hope that something may be accomplished here with the principle of the mechanism of nature, without which there can be no natural science at all. This analogy of forms ... strengthens the suspicion of a real kinship among them in their generation from a common proto-mother, from the gradual approach of one animal genus to the other, from that in which the principle of ends seems best confirmed, namely human beings, down to polyps, and from this even further to mosses and lichens, and finally to the lowest level of nature that we can observe, that of raw matter: from which, and from its forces governed by mechanical laws (like those which are at work in its production of crystals), the entire technique of nature ... seems to derive."
(pg. 287; "Critique of the Teleological Power of Judgment," Sec. 80)
In regards to how this squares with Kant's theory of humanity, I wish to point out that Kant maintains throughout his works (including the third Critique; see Sec. 83, 91) that human beings occupy a special place in the natural world. He establishes early in CPJ that there is Nature (which, for our purposes, could be renamed "instinct") and that there is Freedom (which, again, we might simplify to "free will"), and human beings are the only members of the animal kingdom which are free (i.e. they make their own laws: they are autonomous; they need not be beholden to "natural law" - or instinct). See the "Introduction" (not the "First Introduction") of CPJ for a discussion of Nature vs. Freedom, and check out Sec. 63 for a further discussion of the interconnectedness of nature as well as man's autonomy.
Edit: I googled "critique of the power of judgment" to see if there is an electronic copy of the Critique available on-line, and there does appear to be one in PDF form (it's even the same translation and edition as the one I cited). Just in case it's not legal, though, I'm not going to post a link.
Edit 2: Obelia's link in the comments to the excerpt from which I quoted is good reading if you are looking for additional context. In particular, Sec. 81 has a discussion of two opposing theories which Kant calls "the theory of evolution" and "epigenesis," but don't get confused: what Kant calls evolution is not what Darwin means by it. In fact, epigenesis is much more similar to Darwinian evolution, and Kant has several kind words to say about it.