New biotechnologies promise to revolutionize human existence¯not only by delivering therapeutic treatments and cures but also by offering physical and mental enhancements: creating stronger bodies and more powerful minds for ourselves and for the children we carefully select. Biotechnology will offer us the option of controlling our genetic composition in ways that were previously unimaginable, as we (in British bioethicist John Harris’ words) replace “natural selection with deliberate selection, Darwinian evolution with ‘enhancement evolution.’”
Those bioethicists who, like Harris, express such enthusiasm often dismiss the reservations of critics concerned about biotech enhancement as nothing more than arbitrariness, irrational religious superstition, or, according to Dartmouth professor Ronald M. Green, “status quo bias.” Leon Kass, however, has argued that the gut instincts of the general public should be taken more seriously as embodying a certain “Wisdom of Repugnance.” For many people, though, this wisdom has remained unhelpfully vague.
Technology has outpaced moral reflection. That was a key insight of Harvard political theorist Michael Sandel in his book The Case Against Perfection . Sandel criticized professional bioethicists who were thoroughly entrenched in either a Kantian or consequentialist ethical system: “The familiar categories of autonomy and rights, on the one hand, and the calculation of costs and benefits, on the other” are inadequate, especially when it comes to deciding for what ends biotechnology should be used.
Of course, these options do not exhaust the ethical domain. Natural-law theory, for example, can build on the strengths of both Kantianists and consequentialists. Natural-law theory is teleological¯oriented, like consequentialism, toward promoting the flourishing of human beings. This orientation, in turn, generates certain deontological principles¯principles meant, as are Kantian principles, to protect human beings and the multifaceted aspects of human flourishing.
As such, the account of ethics given by a natural-law theory identifies the various constitutive aspects of human well-being and the moral principles that should direct human action in its pursuit. You can easily see how this helps flesh out the wisdom Kass finds in repugnance.
Yet recent work in natural-law theory, especially as used by Christian thinkers, has largely ignored questions of biotechnology¯except, that is, when they impinge on killing. First with abortion, then with euthanasia and assisted suicide, and now with embryo-destructive research, the hot-button questions in bioethics were well-suited for a natural-law analysis. And natural lawyers responded, developing detailed, nuanced, and persuasive arguments in defense of life.
Or, it might be better put, they did so when it came to defending life against destruction . But natural lawyers have been slow in defending life against enhancements that might not truly enhance.
What might a natural-law appraisal of biotechnological enhancement look like? Much of modern ethics, especially when applied to biotechnology, springs from emaciated views of human nature. In response, a sound natural-law approach would need to begin with a twofold account of the nature of the human person.
The first part would be descriptive: Human persons must be shown to be human animals¯bodily organisms of the species Homo sapiens . And the second part would be normative: Human persons must be shown to be fulfilled by certain ends and harmed by others. Both animality and rationality shape and define the constitutive aspects of our well-being, and critical reflection can identify the various goods that truly perfect us.
Along the way, this two-fold account of the human person would need to stress that personal identity exists across time, from our biological beginnings to our biological endings. Yes, certain characteristically human capacities, such as self-consciousness, take time to develop, and human beings are not always immediately able to exercise them. Still, throughout our entire existence we are human persons fulfilled by certain goods, and we should be treated accordingly.
Once an adequate anthropology is in place, questions of enhancement can be addressed in three steps:
1. The means of enhancement must be scrutinized to determine whether they respect truths about the human person. The basic aspects of human well-being most likely to be damaged by the means of enhancement are the good of life itself and the good of marriage. A natural-law account would exclude biotechnologies that treat nascent human life as nonpersons, mere research material and disposable if not wanted. Embryo-destructive stem-cell research is an example of the former, while discarding genetically unfit embryos after pre-implantation genetic diagnosis in order to select a healthier embryo is an example of the latter.
Meanwhile, because an important aspect of human fulfillment is social¯particularly the unique combination of friendship, sexual union, and reproduction that is marriage¯biotechnologies that undermine the bonds of sociality between the generations and between spouses would also be excluded. Assisted reproductive technologies that replace conjugal union¯rather than assist conjugal union in being fruitful¯do damage to spouses and their children. When human procreation is taken out of the marital union and placed in a laboratory, new life is generated not by the interpersonal communion of spouses but by an anonymous technician. Meanwhile, these same assisted reproductive technologies violate the respect owed to human persons in their origins, as nascent human lives are treated less as persons and more as products¯designer babies.
2. These need not be insurmountable hurdles: New technologies may be developed that will pose no threats to human flourishing as means. A second question then arises about the ends of enhancement. Do the proposed ends of biotech enhancement threaten our nature? Will enhancements truly enhance?
Enhancements must instantiate more thoroughly one of the basic aspects of human flourishing without damaging other aspects or providing mere illusions of fulfillment. For that matter, enhancements must allow ordinary human beings to pursue these avenues of well-being rather than replace our agency with genetic, pharmaceutical, or mechanical alternatives.
Imagine a pill that would give us the feeling of friendship but without helping us form actual friendships. Or think of a computer from which you could download a new personality, with a new biography and new virtues, or a technology that would alter minds to eliminate crime.
In all these, the acts of the will that define our character would be gone. The prospect of a world in which everyone acts virtuously is promising only if it is a world in which everyone truly acts . Since acting freely requires reason, a sound natural-law account would need to pay particular attention to the physical substratum of rationality in animals. Even if rationality is in its essence immaterial, we must be careful not to alter the physical makeup of human beings in a way that will damage or diminish our brain’s ability to support it.
One should not draw the conclusion that natural law’s appraisal of biotechnology must be negative. There are real threats¯to life and marriage, to our relations to certain goods, and to our ability to judge and choose. But they are not insurmountable, if the bodily changes do not injure our relations to the basic aspects of human flourishing and our active ability to pursue them.
Thus, some “enhancement evolution” might, within certain bounds, be ethical. Improvements of health, for example, or of our perceptual abilities and our bodily configuration. Such changes might genuinely result in new opportunities to pursue the same human goods in creative ways.
3. Still, even if some biotechnology poses, in principle, no problems in its means or ends for isolated use, a third set of questions must be raised¯questions about culture and prudence. What sort of a people is it desirable for us to be, and how will we become such a people? How might widespread biotech usage shape society?
None of us lives in a vacuum, and once certain biotechnologies become commonplace, all of us will reap the consequences. As biotechnology changes our self-understanding, new lessons will be passed on to future generations about what living the good life entails. In fact, new biotechnologies could redefine what it means to be human and eliminate the social structures that shape our traditional outlook on life. As biotechnologies spread, they have the potential to convince people that our fulfillment lies in material and physical perfection¯not in the spiritual and moral perfection of a virtuous life.
The final moral hurdles of enhancement are matters of ethical culture. Can we sustain a cultural hold on conceptions of genuine human well-being, rather than embrace a thin and unsatisfactory hedonism or relativism?
This is just an outline of what a natural-law account of biotechnological enhancement needs to consider. In the latest issue of the New Atlantis , we address these issues in greater detail.
Ryan T. Anderson is assistant editor of First Things and a Phillips Foundation Fellow. Christopher Tollefsen is an associate professor of philosophy at the University of South Carolina and coauthor, with Robert P. George, of Embryo: A Defense of Human Life 
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