One of the current problems with discussing things about marriage, transgenderism, homosexuality, and related issues is a relatively unsatisfactory degree of agreement about what it is to be “human”. And this poisons a lot of the discussions.
The ordinary “definition” I use is the one that Aristotle and St. Thomas Aquinas generally applied, man is a rational animal. To give a proper and complete definition of a substance is to give state all 4 of the kinds of cause for the thing, but primarily it is to state the “nature” of the thing, which is given by its form and matter – its formal and material causes. For a natural thing, it suffices, then, to state the genus in which the thing’s species is found, and the specific difference that differentiates it from all other species in the genus. Man is in the genus animal (which implies the material aspect), and he is different from all the other species by the fact that man is rational.
I don’t posit this as if it were undebatable, for others surely bring up problems with that definition. For the purpose of this discussion, it is sufficient to note that this is a reasonable attempt and a widely held classical definition. What I find interesting about it is that it often goes unnoticed that if this is the proper definition of man, it would imply that “animal” is the lowest possible genus above the species 'rational animal'.
This matter is taken up somewhat in an interesting article by David Oderberg in discussing whether there can be enhanced beings derived from humanity so that they would be a different (superhuman) species.
There is a lot to like about this article, including Oderberg’s discussion of the philosophical difficulties involved in “the species problem”. It’s not surprising that I would like much of what he says: like me, Oderberg is Aristotelian. However, I do not agree with some rather significant points in this article. While he excellently draws out the reasons why “rational animal” is a good definition, I think he lets it get away from him in concluding that no special morphological characteristics of humans is critical, and so ANY rational animal would belong to the species ‘man’. Hence (for the purpose of his article), any super enhanced living animal beings from man would still be part of our species.
While I largely tend to agree with Oderberg about enhanced post-human beings, I still think his claim that ANY rational animal would be human can be shown to be wrong both using revelation and via philosophy / theology, but I suspect the former is easier so I will start there.
In Genesis, in the VERY NEXT SENTENCE after God making man “in his image” (which Thomas and many other scholars take as a reference to man’s rationality), then says “Male and female he made them.” I say that “being in 2 sexes” is, also, part of the specification of man, part of his essence. The Bible puts it right there alongside the “in his image”, so it is at least reasonable that it too is specifying what ‘man’ is. If there some other planet with creatures, (of which Scripture does nothing to speak for or against), and if on that planet God had created beings “in his image” but in 3 sexes, they would NOT be human.
The other argument works sort of from JPII’s theology of the body. Significantly, Thomas Aquinas and JPII both taught that man’s end is in loving*. Specifically, in loving God, and derivatively in loving man as a reflection of God. But in our human condition here on Earth before the Final Judgment, the highest human love we can have here is that of husband and wife who are lovers (in the physical and romantic sense) and friends, and is definitively expressed in the conjugal act of love.
The reason this is important to the discussion is that the format of man’s love in marriage is special to the species of man. (Note: no non-rational animal loves in the proper sense: they are not rational, and cannot act out of the RATIONAL appetite that is the will, as love.) In marriage, the conjugal act is and can only be the physical act of love that regards the other spouse here present and the potential child that may come to be. Both aspects of that regard are ultimately ordered toward God: in His providence, He designed the human act of love to call forth a kind of image of God as under community of the Trinity, which is also a community of love. Indeed the Trinity is the paradigm community of love.
Yet, I submit, because man in his marital love presents AN image of God, a KIND of reflection of Him, and not a perfect (i.e. complete) one, there could be completely different ways for rational animals to operate as an image of God. For instance, God could design a creature which reproduces via 3 distinct sexes, in which their operation of love reflects an image of God under a different mode than the one in which human sexual love does.
Let’s call such creatures tripplers. I argue that tripplers would be essentially different from humans, and that they would have to be called a different species. While it is true that man’s rationality is essential, and identifies a critical feature in which man is different from all the other animals that we know of, it is not impossible logically that there might be some FURTHER facet of man, within rationality, that is special to him that says “what he is”. And, I claim, man being put together so as to reflect God in sexual love via 2 sexes is distinctive to man and essential to him. Man’s highest love in the human sphere being that of sexual love for ONE spouse, is part of the meaning and definition of marriage: it is unique, singular, and
Interestingly, we might also posit God making a rational animal which reproduces not by sexual interaction at all, but more as “budding” or in some other non-sexual fashion. This format of rational animal would reflect God in a completely different way than man and tripplers do, (which both would entail the love of spouse and both reflect God as regarding community). Perhaps such unitary beings would better reflect God’s oneness, and self-sufficiency. In any case, they certainly would constitute a different species than man or tripplers.
Note that while the differences I posit between man and these other species show up in important morphological differences, those outward differences are not the heart of the distinction I am claiming proves their diverse species. That is proven rather by the special way in which their rational behavior in love is a reflection of God.
A possible objection to this conclusion is that such beings could all be the same species because they can all enjoy the same community: in loving God as rational beings, they are able to inhabit the same sphere by recognizing in each other fellow members having the same ultimate end. The answer to this is a counterexample: that humans share the same conditions with angels, who also are rational and love God, and with whom we will share heaven in community. Yet angels certainly are NOT the same species as humans, they are not even within “animal”, having no earthly bodies.
Finally, what this means is that the description of man as “rational animal” is accurate insofar as it goes, but is incomplete. In a world in which there is no other example of rational animals, merely pointing out that man is rational separates him from other animals quite well. But if there were rational animals in one or 3 sexes, then it would no longer be sufficient. This implies that the lowest genus above ‘man’ is not ‘animal’ but something below that.
I would note that I mostly agree that enhanced beings derived from man will be “human”: as long as they are derived in such a way that the 2 sexes remain fundamental to how man loves while here on earth, I would agree that they remain human. If, however, there were some crazy and (to date unimaginable) way of modifying the human body so that it’s sexual love really were made into 3 sexes – and where all three were essential and distinct – that would represent a different species. For philosophical reasons, I don’t think it possible for man to successfully accomplish such a thing, I believe that such a level of control of nature can be achieved only by God (not even angels). Hence, I don’t think there will ever be enhanced beings derivative from man who manage to leave behind all vestige of being “in 2 sexes”, though we could so damage future humans so that they cannot successfully express love via sexual love – since such a defect is already present in some humans, without causing them not to be human.
Any other new “speciation” difference possibility would have to represent a change that gets at something _essential_ to what man is and how he acts. And it is hard to envision what that might mean*: the 2 “rational” faculties are those of the intellect and the will, and something important enough to be regarded as essential rather than accidental has to be something that fundamentally alters man’s intellect or will in how they operate properly. Merely knowing God as “the Creator of tripplers” rather than as “the Creator of humans” is not an essential difference to the intellectual operation – since if we came across tripplers in outer space we could also know God as “the Creator of tripplers”. You could say the words that claimed a possible intellectual difference in a hypothetical animal creature that did not come to knowledge of the world through sense faculties, but I doubt that you can actually construct a positive concept of such a being, it would be rather merely the incomplete concept of “having animal rationality but not with senses”, but this is mere negation, not a positive way of being.
This leaves somewhat open the question whether lesser differences (such as the types of morphological differences that David Oderberg discusses: having more arms, or tentacles) would be enough to differentiate separate rational species of animals. Oderberg says no, and I am sort of inclined to agree with him on the philosophical basis that such features do nothing important to differentiate the _rationality_features of such animals: you wouldn't have a genus 'rational animal' and have this be the dividing difference between species within that genus. But I am not confident that this is the correct way of proceeding. In identifying distinct species of animals, logically speaking it seems possible that the same lower difference can be present in 2 different genera: the differentiating feature of “having A” or “not having A” can happen both in Genus X and in Genus Y. (Consider, as a similar type of situation, in the genus ‘four-sided polygons’, the features of ‘having equal sides’, and ‘having right angles’, and ‘having parallel sides’: depending on which feature you take higher and which lower, ‘rhombus’ and ‘square’ can be side-by-side species in the genus “four-sided parallelograms with equal sides”, but alternatively ‘rectangle’ and ‘square’ can be side-by-side species of the genus ‘right-angled parallelograms’ and ‘rhombus’ would not be a coordinate species there.) And if so, then you might logically find ‘rational’ as the differentiating feature of species in two completely different genera.
This could actually be argued plausibly in the case of dolphins, who are clearly not in the same ‘infima genus’ of man, if man is in ‘primate’ for example. I for one would not want to be the one on the spot for proving beyond a shadow of a doubt that dolphins are not rational. Some of the behaviors that we see in them are hard to fit with ‘non-rational’. If the true and principled divisions of genera into species over and over were such that it is fundamentally and philosophically impossible for ‘having A’ and ‘not having A’ be the differentiation in two separate genera, then it would have to be the case that ‘rational’ versus ‘not-rational’ could only be a division within one genus, and it would be far harder to argue that dolphins and man are in the same LOWEST genus, even though clearly man is with the primates and dolphins are with the cetaceans. But I don’t know of any successful way to establish such a philosophical thesis, and I doubt it is really valid.