From Aristotle to Darwin and Back Again: A Journey in Final Causality, Species and Evolution
comments:
And this agrees with the former book, in which Oderberg distinguishes between a phylogenetic understanding of species, and an ontological understanding. The traditional ontological definition for "human" is "rational animal". It is composed of the genus "animal" and the specific difference "rational" that differentiates the human species from among the other species in the genus "animal"[2]. Under this traditional way of defining species, rational life on other planets would, therefore, qualify as human. "The aliens" would be, in some sense, "one of us", even if they were to differ phylogenetically. This becomes quite interesting in the context of an analysis along the lines of Aristotle's "De Anima", as, for example, rationality has definite entailments when it comes to anatomy and physiology.
[2] I am using the terms "genus" and "species" in the relative, ontological, intensional sense[3], not the narrow biological sense, as more or less meaning "broader category" and "narrower subcategory", respectively. Thus, we can say that the species of triangle is a plane figure that has three straight bounding sides, where "plane figure" is the genus, while having three straight bounding sides is the specific difference.
[3] https://en.wikipedia.org/wiki/Genus%E2%80%93differentia_defi...
The first thing to note is that evolution does not necessary contradict telos. The metaphysical position called evolutionism does by definition, but evolution as biological subject matter does not.
Second, the question about the stability or reality of human nature is separate from the question of telos. Even if we suppose that there is no such thing as human nature, we would still need to admit kinds, each with some telos, but more importantly, the very notion of efficient causality already presupposes telos. Without telos, you cannot explain the regularity of the effects of efficient causes. The effects of efficient causes are not arbitrary, or else science would be impossible. And biology, per my observations, is showing signs of slowly moving toward open acknowledgement of telos. The notion of "function" is teleological, after all!
Third, it is odd to speak of human nature changing. For if there is such a thing, then it is predicable, and predicates do not change. You seem to be making a nominalist sort of claim, i.e., the collection of beings, over time, that we have, for whatever reason, classified as "human" do not actually share the same nature. I cannot make heads or tails of nominalism, nobody can, because I cannot determine why the label "human" was used in the first place and why a mislabeling should be regarded as something significant, as something more than a mislabeling. Nominalism renders the word unintelligible. You might say "Oh, well, we have adaptation!", and I would agree, that human beings have adapted and continue to adapt, but the nature of a thing concerns what is essential or substantial about something. Everything else is either a proper consequence of that (speech), or an accidental adaptation or variation (eye color). As a metaphysician would say, intelligent beings on other planets are, ontologically speaking, also human by virtue of their intellects, even if phylogenetically there is a difference. So, the nominalist claim doesn't even rise to the level of being wrong. I claim that there were humans thousands of years ago, and there are human beings today, and because both instantiate the same human nature.
In any case, Etienne Gilson has written a book[0] on this subject. I wouldn't call it a magisterial or exhaustive philosophical work on the subject (others have produced better [1] if you want more heft), but as an introduction to some basic ideas, IIRC, it isn't bad.
[0] https:/&