In my last post, I said that husband and wife are “one flesh, one organism, biologically related.” This claim is at the heart of the Church’s opposition to governmental recognition of same-sex unions, but it is hard to understand. How are the two “one flesh” when one of them goes to the office and the other to the grocery store at the same time? How are the two biologically related when they are not even cousins? How are they “one organism” when one can die without the other?
To break into the problem, we have to look at how humanity and biology are related in general. Human beings are rational, that is, they have a spiritual dimension that allows them to see the true and choose good or evil. And yet human beings are at the same time bodily and biological, sharing common ground with animals and even with plants and micro-organisms. We tend to think of these two dimensions as glued together somewhat awkwardly, with the rational part being the “real me” who tries, sometimes with more success and sometime with less, to control and direct the biological part.
But in fact our rationality shoots all through our biology and vice versa. We share eyeballs and the neurology of vision in common with higher animals, and yet we see in a rational way: we enjoy the structure and beauty of art in a way that animals simply do not. We hear music in a way that animals do not. We have desires for food and sex like animals do, and yet the goal of growth in virtue is to have these desires shot through with rationality so that we desire in a rational way. Going the other way, our reason is helpless without imagination based on the senses, and our immaterial will needs the prodding of animal desire to prompt it into action. We are not rational over here and biological over there: we are rational-biological. That’s what we mean when we say we are rational animals.
Marriage is a wonderful instance of this general fact. Biologically, a man and a woman are each incapable of reproduction without the other, each deficient in instincts for life without the other, and each in need of the kind of emotional stimulus and support the other provides. When a man and a woman have sexual intercourse, they share a single biological function, namely reproduction, becoming in a way one organism. This establishes an ongoing relationship in which their many other levels of complementarity come into play: even after the child is conceived and born, the man and the woman continue to play complementary roles in a single action, both the action of completing what they have begun by getting the baby to adulthood and the simple action of living their everyday lives.
But the biological reality is shot through with rationality. Masculinity is not just a way of begetting children but a way of being human; femininity is not just a way of performing a biological function but a way of being rational. The joining of the two in a single biological function is at the same time a spiritual giving of each to the other expressed through the body. The emotional needs each supplies actually tie in to the life of virtue and growth toward God.
Consequently, a union can fail to be “marriage” from either direction, by failing in rationality or failing in biology. On the one hand, even sexual intercourse does not bring about a marriage if the man and the woman do not will that it should: rape lacks the consent of one party entirely, and shacking up lacks the seriousness of consent demanded by the occasion. To be entirely clear: rape and fornication and adultery are all unnatural because the rational part is missing. Human beings are both rational and biological by nature, and a union that lacks the rational side falls short of the natural even if the correct body parts do all the right things.
On the other hand, the most intense will to union does not bring about a human marriage without that sharing of a single biological function in the reproductive act. Same-sex activities in bed, heterosexual activities that don’t involve actual union, and all that kind of thing are also unnatural because they lack one side of the human rational-biological unity.
All of this should, I hope, clarify the Church’s response to the standard objection about heterosexual couples who cannot conceive children. Since their sexual activities are infertile, how are they different from a same-sex couple in bed? Simply put, the infertile heterosexual couple does not separate the rational and the bodily. They consent to their union as rational beings, and they share a single organic function as bodily beings; they are united in soul and body. The fact that their shared organic function is defective does not hinder their sharing it and so becoming one body: it just means that their one flesh is defective in some way that prevents offspring.
Here’s a far-out analogy. Suppose men and women were made each with one leg, and suppose that in marriage they became “one flesh” in such a way that each supplied a leg for the other so they could walk. Now suppose that one of them has a bad ankle, and he limps. This doesn’t mean that they don’t walk together as one, but just that they limp when they do.