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The deliberate use of biomedical or technical means to extend human capacities beyond what is needed to restore or maintain ordinary health.
Human enhancement is the deliberate use of biomedical, pharmacological or technical means to raise a human capacity above the level required for ordinary health, rather than to restore a capacity lost to disease or injury. The category is defined by contrast: an intervention counts as enhancement when it is not therapy. That contrast turns out to be hard to draw cleanly, which is why most of the philosophical work on the subject is about the boundary itself rather than about any particular technique.
The standard way of drawing the line appeals to species-typical functioning. On Christopher Boorse's biostatistical account, health is the statistically normal contribution of each organ and process to survival and reproduction for an organism of a given age and sex; disease is subnormal functioning, and medicine's job is to restore the norm.1 Norman Daniels built a theory of just health care on a similar footing: society owes its members treatment that protects the normal opportunity range, and enhancement beyond it is a private matter.
The account has clear uses. It explains why insurers pay for insulin and not for a cosmetic procedure, and why growth hormone for a child with a pituitary tumour is treated differently from growth hormone for a healthy short child. It also fails in predictable places. Vaccination raises immune competence above the untreated norm and is universally classed as medicine. Contraception disables a functioning system. Reading glasses correct a deficit that is statistically normal after 45. Caffeine is a cognitive enhancer taken daily by most adults in industrialised countries and is not regulated as one.
| Dimension | Therapy | Enhancement |
|---|---|---|
| Reference point | Species-typical function | Whatever the person wants |
| Typical justification | Restoring normal opportunity | Autonomy, welfare, competitive gain |
| Who usually pays | Insurer or state | The individual |
| Regulatory pathway | Approval against a disease indication | Off-label, supplement, or unregulated |
| Evidence usually available | Randomised trials in patients | Small studies in healthy volunteers |
Two repairs are commonly proposed. One replaces the species norm with the individual's own prior baseline, which handles spectacles and vaccination but makes enhancement depend on when the measurement is taken and cannot classify anything done before birth. The other abandons the boundary in favour of a direct welfare test: an intervention is justified if it makes the person's life go better, whatever the statistical norm. That test is what proponents of enhancement generally endorse, and its weakness is measurement, since well-being over a lifetime is exactly the quantity no trial is powered to detect.
Buchanan, Brock, Daniels and Wikler concluded in From Chance to Choice that the distinction cannot bear the moral weight often placed on it, but that it remains useful as a rough guide to what a health system is obliged to provide.2 That is roughly the mainstream position twenty-five years later: the line is administratively real and philosophically porous.
Terminology"Enhancement" is used in at least three ways in the literature: exceeding species-typical function, exceeding an individual's own prior baseline, and improving a capacity by any means including training. Arguments frequently trade on the ambiguity, since almost nobody objects to the third sense.
Enhancement is not one technology but a set of routes that differ in reversibility, cost and who bears the risk.
Pharmacological. Stimulants, wakefulness-promoting agents and putative cognitive drugs are the most widely used route, discussed in Nootropics. A 2008 informal poll of Nature readers found that about one in five respondents reported using prescription drugs for non-medical cognitive purposes, a figure often quoted and rarely replicated in representative samples.3 Serotonergic psychedelics are often counted here as well, but the trials collected under Psychedelic therapy enrol patients with a psychiatric diagnosis rather than healthy volunteers, so they establish nothing about enhancement. Anabolic agents and blood-oxygen manipulation dominate Enhancement in sport.
Genetic. Selection is available now and editing is not. Polygenic embryo screening ranks existing embryos on statistical predictors; Human germline editing would introduce heritable changes and remains prohibited for clinical use in most jurisdictions. The limits of both for complex traits are set out in Genetic enhancement of cognition and Designer babies: the traits people most want to enhance are influenced by thousands of variants of tiny effect, which caps what selection can deliver and makes editing impractical.
Cybernetic and sensory. Brain–computer interfaces are being developed as assistive devices for paralysis, with enhancement of healthy users a stated long-term aim of some companies and a distant one on current bandwidth. Sensory augmentation adds channels rather than restoring them, and Non-invasive neuromodulation is the modality with the largest gap between consumer marketing and replicated evidence.
Physical and metabolic. Myostatin inhibition, powered exoskeletons, and interventions aimed at Healthspan rather than disease sit at the boundary where geroscience meets enhancement, since delaying biological aging in a healthy person is by definition not treating a diagnosed illness. Use of incretin drugs by people at or near typical weight is the current mass-market instance of the same boundary.
Moral and affective. Moral enhancement proposes to alter dispositions rather than capacities, and raises objections that do not arise for the others.
The affirmative arguments come in three broad families.
The welfarist argument holds that if an intervention makes a life go better and harms no one else, the burden of proof lies with those who would prohibit it. John Harris pushes this to an obligation: where enhancement is safe and effective, declining it is not neutral but a failure to make things better.4 Julian Savulescu extends the same logic to reproduction under the heading of Procreative beneficence.
The continuity argument observes that literacy, numeracy, vaccination, spectacles and caffeine are all enhancements by any consistent definition, and are unobjectionable. If the biomedical versions differ, the difference must be located in something other than the fact of enhancement.
The evolutionary-slack argument, developed by Nick Bostrom and Anders Sandberg, answers the reply that natural selection has already optimised human biology. Selection optimises for inclusive fitness in ancestral environments, not for welfare in modern ones, and it faces constraints that engineers do not. Their "evolutionary heuristic" specifies when to expect exploitable slack: where the environment has changed, where a trait was costly in ancestral conditions but is cheap now, and where evolution faced a tradeoff that technology can relax.5
The strongest objections are not about safety.
Giftedness. Michael Sandel argues that the drive to enhance expresses a refusal to accept the unbidden, and that a world in which children's traits are chosen erodes the humility and solidarity that follow from recognising talent as unearned luck.6 The argument is not that enhancement harms the enhanced but that it corrodes social attitudes toward those who are not.
Dignity and the given. The President's Council on Bioethics under Leon Kass framed the concern as a set of questions about whether achievements obtained pharmacologically are the agent's own, and whether a life without limits retains the shape that makes human goods intelligible.7 Jürgen Habermas argues separately that a person whose genome was designed by another stands in an asymmetric relation to that designer, compromising the sense of being the sole author of one's life.
Authenticity and complicity. If a capacity is bought rather than developed, some of what made it valuable may be lost. Critics note that this objection proves too much when applied to education or to coffee, and defenders reply that it applies with different force to interventions that bypass effort entirely.
The bioconservative case is set out at length in Bioconservatism and the argumentative structure of the whole debate in Bioethics of enhancement. Two points are worth separating from the rhetoric. First, several bioconservative predictions about safety have held up: the biology has been harder than proponents expected, and the most confident enhancement claims of the 2000s have not been realised. Second, the disability-rights critique in Disability rights and enhancement is not a version of the giftedness argument; it concerns what a society communicates when it treats certain ways of being human as defects to be engineered out.
The distributional worry is straightforward. Expensive interventions reach the wealthy first, and if they compound across a lifetime or across generations, existing inequality becomes biological. Access and inequality examines how strong this effect is likely to be against the historical record of expensive medicine, which has usually diffused, and against gene therapies priced above a million dollars per dose, which so far have not.
The coercion worry is structurally different and, in the view of many philosophers, more serious. Where a capacity is positional, its value depends on others not having it. Once enough competitors take a wakefulness drug, declining it becomes a cost rather than a neutral choice, and formal voluntariness does not describe the situation. This is the collective-action problem analysed in Enhancement arms race and the reason anti-doping regimes exist at all despite their expense and their intrusions.
Where the disagreement actually liesFew participants in this debate hold that enhancement is intrinsically wrong or that it is unconditionally permissible. The live disputes are about who bears the risk, whether consent is meaningful under competitive pressure, and whether the state should fund, permit, discourage or prohibit each modality separately.
No jurisdiction regulates enhancement as a category. Drugs are approved against disease indications and then used off-label; devices are cleared for clinical purposes and marketed to consumers under wellness exemptions; supplements marketed for cognition face only post-market enforcement. The practical consequence is that the safety evidence for enhancement use is generated mostly in patients who are not the people taking it, and that risk information for healthy users is thin.
Three areas have developed dedicated rules. Sport prohibits a defined list of substances and methods and grants therapeutic-use exemptions, making it the one domain that draws an operational therapy–enhancement line and litigates it. Military programmes in several states fund performance sustainment research under separate ethical review. And neural data has begun to attract specific law, discussed in Neurorights and Mental privacy, because neural interfaces intended as assistive devices generate information about people that no prior consumer category anticipated.
The empirical bottleneck is that the enhancement effects demonstrated so far are small, heterogeneous and measured on laboratory tasks whose relation to performance outside the laboratory is weak. Almost every well-controlled study of a cognitive enhancer in healthy adults reports effect sizes that would be unremarkable in a study of sleep or exercise, and often larger gains in people starting from a lower baseline than in high performers, which inverts the usual assumption about who benefits.
The conceptual bottleneck is that the therapy–enhancement distinction does most of the administrative work in medicine and almost none of the moral work, yet no replacement has been agreed. Proposals to substitute a welfare criterion founder on measurement; proposals to substitute a species-norm criterion founder on the cases above. What follows if the distinction is abandoned entirely, and whether health systems can function without it, has not been worked out by either side.
paperBoorse, C. "Health as a Theoretical Concept." Philosophy of Science, 1977. ↩
bookBuchanan, A., Brock, D. W., Daniels, N. and Wikler, D. From Chance to Choice: Genetics and Justice. Cambridge University Press, 2000. ↩
paperMaher, B. "Poll results: look who's doping." Nature, 2008.↩A self-selected online poll of Nature readers rather than a representative survey, so the one-in-five figure has no sampling frame behind it.
bookHarris, J. Enhancing Evolution: The Ethical Case for Making Better People. Princeton University Press, 2007. ↩
bookBostrom, N. and Sandberg, A. "The Wisdom of Nature: An Evolutionary Heuristic for Human Enhancement." In Savulescu, J. and Bostrom, N. (eds), Human Enhancement. Oxford University Press, 2009. ↩
bookSandel, M. J. The Case Against Perfection: Ethics in the Age of Genetic Engineering. Harvard University Press, 2007. ↩
reportPresident's Council on Bioethics. Beyond Therapy: Biotechnology and the Pursuit of Happiness. Washington, DC, 2003.↩An advisory report from a body appointed by the US president and chaired by Leon Kass; it argues a philosophical case rather than reviewing evidence.