St. Thomas Aquinas describes sexual differentiation as a part of man’s animal nature. But this does not mean that human beings have sexual differentiation as the other animals have it. This is a mistake that comes from a too-literal understanding of the classical description of man as a “rational animal,” where “rational” merely modifies, adds to, or is otherwise extrinsically related to “animal.”
The best intention in this view is the desire to ground the beliefs and behaviors that concern our sexual difference firmly in “nature” and orientated towards reproduction. The practical syllogism seems to work like this: Sexual difference, in animals, is clearly orientated towards the reproduction of their species; man is an animal; therefore man ought to orientate his sexual difference towards the reproduction of the human species, rather than indulge in acts contrary to this natural end.
The conflation of animal and human sexual difference seems to serve the Christian reaction against the transgender movement through a similar line of reasoning. It is obvious that the body of the animal, understood as tending towards a unique role in reproduction, confirms…
