I can't say categorically, but at least in his main works, Descartes did not seem to write anything of substance (pun intended) on the origin of biological species. Humans do occupy a special role in Descartes's philosophy, but, as a rule, it is humans as rational beings, not humans as biological beings. Here are two places where he briefly comes close to (and immediately steers away from) the subject of species. In the Meditations, at a stage where he inquires "what type of being am I" he momentarily considers Aristotle's definition of human beings as rational animals, but then rejects it as "too subtle" for his (Descartes's) own purposes.
What then did I formerly believe myself to be? Undoubtedly I believed myself to be a man. But what is a man? Shall I say a reasonable animal? Certainly not; for then I should have to inquire what an animal is, and what is reasonable; and thus from a single question I should insensibly fall into an infinitude of others more difficult; and I should not wish to waste the little time and leisure remaining to me in trying to unravel subtleties like these. But I shall rather stop here to consider the thoughts which of themselves spring up in my mind, and which were not inspired by anything beyond my own nature alone when I applied myself to the consideration of my being.
Another place where we should have expected Descartes to present his views on biological species, if he had any, is in the Principles, where Descartes laid out the principles of science, based upon his epistemological and metaphysical foundations. Descartes did present, in fact, a foundation for physics, but much less for biology. And he tells us, in fact, that he planned to dedicate two additional parts of the Principles to living beings: plants, animals and human life. This plan, however, did not actualize. According to Descartes himself, he did not feel ready for it.
I should add nothing further to this the Fourth Part of the Principles of Philosophy, did I purpose carrying out my original design of writing a Fifth and Sixth Part, the one treating of things possessed of life, that is, animals and plants, and the other of man. But because I have not yet acquired sufficient knowledge of all the matters of which I should desire to treat in these two last parts, and do not know whether I ever shall have sufficient leisure to finish them, I will here subjoin a few things regarding the objects of our senses, that I may not, for the sake of the latter, delay too long the publication of the former parts.
(*) The Principles of Philosophy were published in Latin in 1644, and in French in 1647, three years before Descartes's death. So they seem to be quite authoritative as to Descartes's mature views.