I must admit, however, that I have not done a thorough study of how Aquinas uses Aristotle's biology in all of his writing. So I was pleased to discover a dissertation that studies how Aquinas uses Aristotle's biology in his account of marriage. Eric M. Johnston wrote a dissertation in 2009 for his Ph.D. in theology at the Catholic University of America, the title of which is "The Role of Aristotelian Biology in Thomas Aquinas's Theology of Marriage." Johnston is now a professor of theology at Seton Hall University. His dissertation is a wonderfully insightful study of all the places in Aquinas's writing where he speaks about marriage, sexuality, and parenthood, and he shows how Aristotle's biological comparisons of human beings and other animals are used by Aquinas to support his understanding of sexual mating and parental care. Johnston's general conclusion is that "Thomas is able to account for all the main Catholic doctrines on marriage through parallels between human and animal procreation" (44).
I agree with Johnston on most of the points he makes. But I disagree on some points.
I agree with the core of Johnston's dissertation, which is to show how Aquinas carefully employed Aristotle's biological writings--especially, The Generation of Animals and The History of Animals--in using animal biology to explain human sexuality, marriage, and parenting. He shows that even when Aquinas does not directly cite Aristotle, Aquinas often uses examples from Aristotle's biological observations.
For example, one of the most important Biblical texts for the Christian doctrines about marriage is the seventh chapter of Paul's First Corinthians. Paul begins this chapter by writing:
Now concerning the matters about which you wrote. It is well for a man not to touch a woman. But because of the temptation to immorality, each man should has his own wife, and each woman her own husband. The husband should give to his wife her conjugal rights, and likewise the wife to her husband. For the wife does not rule over her own body, but the husband does; likewise the husband does not rule over his own body, but the wife does. Do not refuse one another except perhaps by agreement for a season, that you may devote yourselves to prayer; but then come together again, lest Satan tempt you through lack of self-control. I say this by way of concession, not command. I wish that all were as I myself am. But each has his own special gift from God, one of one kind and one of another. To the unmarried and the widows I say that it is well from them to remain single as I do. But if they cannot exercise self-control, they should marry. For it is better to marry than to be aflame with passion. (I Cor 7:1-9)
In Aquinas's Commentary on First Corinthians, one of the remarkable features of his commentary on this passage is that he introduces biological comparisons with other animals (from Aristotle's biological writings), although Paul says nothing about this. Aquinas writes:
Natural reason teaches that man use the act of generation according as it is suitable for generation and education of children. But in brute animals, it is found that in certain species the female alone is not sufficient for the training of the offspring, but the male takes care of the offspring with the female. For this, it is required that the male recognize its offspring. Therefore, in all such animals, as doves, pigeons, and the like, solicitude for the training of offspring is inspired by nature. Wherefore, in such animals, intercourse is not random and indiscriminate, but a definite male is joined to a definite female, not one to another promiscuously, as happens in dogs and such animals, in which the female alone takes care of the offspring. But above all in the human species, the male is required for the education of the offspring, which are attended to not only regarding bodily nourishment, but to a greater degree regarding the nourishment of the soul, as it says in Hebrews (12:9): "We have had earthly fathers to discipline us and we respected them." And consequently, natural reason dictates that in the human species intercourse is not random and uncertain, but is by a definite man to a definite female, who in fact made the arrangement through the law of matrimony.
Thus, therefore, matrimony has three goods. The first is that it is a function of nature in the sense that it is ordered to the production and education of offspring; and this good is the good of offspring. The second good is that it is a remedy for desire, which is restricted to a definite person; and this good is called fidelity, which a man preserves toward his wife, by not going to another woman, and similarly the wife toward the husband. The third good is called the sacrament, inasmuch as it signifies the union of Christ and the Church, as it says in Ephesians (5:32): "This mystery is a profound one, and I am saying that it refers to Christ and the Church."
That comparison of human beings with other sexually reproducing animals states the main principles of Aquinas's teaching on sex, marriage, and familial bonding. Like other animals, human beings are driven by a powerful natural desire for sexual mating. Like other animals whose offspring cannot survive or flourish without parental care, and for whom the care of both parents is often necessary, there is a natural need for long-lasting bonding between the mother and the father for the care of the young. But the parental attachment of the father depends on his confidence that he's caring for his own children rather than the children of another man. This must be so, because love of children is an extension of our self-love, so that we love our children as our own. Even adoption requires some such special attachment so that our adopted children seem to be our own. For human children, parental care includes not just bringing children into existence but also feeding them and educating them, because children need a long period of social learning before they can live as mature young adults.
As thus rooted in human biological nature, human marriage has two natural goods--the good of parental care and the good of spousal love.
For Catholic Christians, there is a third good of marriage that is supernatural--the good of marriage as a sacrament of the Church in symbolizing the supernatural mystery of Christ's marriage to the Church as His bride.
It seems, then, that while the first two goods are matters of natural law as rooted in the biological nature of human beings as sexually reproducing animals, the third good surpasses natural law because to recognize marriage as a sacrament, we need the divinely revealed law of the Bible.
But then we might wonder how far Thomas's Aristotelian biology goes in supporting the Thomistic natural law teaching as grounded in natural experience and reasoning without need for divine revelation. We might also wonder how far modern biological science could support this teaching. On both points, I go farther than Johnston wants to go. I'll explain this in my next post.