What do we mean when we speak about human enhancement? New York University professor Wafaa Bilal recently had a video camera implanted on a titanium base in the back of his skull. Leaving wires dangling awkwardly along his neck, the camera sent images to a remote server every 60 seconds. Students' concerns over their privacy, faced with a teacher who for once really did have eyes in the back of his head, forced Bilal to wear a lens cap while teaching, somewhat defeating the point.

A few months later an infection forced Bilal to remove the camera, and simply wear it around his neck, but he remains keen to have it back in his skull as soon as possible. Why? What is the difference, you might wonder, between a camera strapped to someone's neck and the same camera attached to the skull with a titanium plate? To Bilal, it is all about a demonstration of 'commitment', making the painful surgery and risk of infection worthwhile. Bilal's messy piece of DIY illustrates some of the challenges around popular perceptions of human enhancement.

Australian artist Stelarc has grown a third ear in a lab and inserted it into his left forearm. Nina Sellars' arresting photographs of the process are on view in HUMAN+. Stelarc hopes to insert a bluetooth microphone into the ear so people all over the world can listen in to his conversations over the internet, though the completion of this aspect of the project has so far been delayed by infection.

For a small fee, body artist Steve Haworth will provide you with small magnets implanted in your fingertips so you can "feel" the presence of magnetic fields. Cybernetics Prof Kevin Warwick hit headlines when he had an RFID chip implanted in his arm to allow him to open and close doors, prior to more sophisticated experiments on direct neural/electronic interfaces. Warwick caused even more controversy when he reportedly suggested that an 11-year-old girl should be "chipped" with a tracking device in the wake of the Soham murders, in a similar manner to pet dogs and cats.

These stories have perennial fascination for the media, perhaps less for the "superpowers" of their protagonists, which could arguably be accomplished through less radical interventions, and more for their disturbing transgressions of the boundaries of the human body. We seem to fantasise endlessly about cyborgs – Robocop-style human-machine hybrids – but many of the dimensions of human enhancement are far more subtle and pervasive.

Humans have always been augmenting their senses, physical powers and cognitive abilities through ingenious tools and technologies. The Hubble telescope, functional magnetic resonance imaging and atomic force microscopes can be viewed as extensions of the senses, just as our newfound ability to gather "swarm intelligence" about developments in Libya or Japan instantaneously through social media is an extension of the campfire conversations of Neolithic man. We are continually developing new ways to see the invisible, to share knowledge and conduct our social lives remotely. In attempting to defeat ageing processes, cosmetic surgery promises to extend youthful appearance as Viagra promises to extend our sexual activity into old age.

Why shouldn't we consider contact lenses, mobile phones, watches and bicycles as human enhancements? Going back further still, the invention of writing itself, as recounted by Plato in a famous passage in the Phaedrus, was an enhancement that simultaneously extended and impaired human memory, by providing an externalised written record but diminishing people's ability to memorise by removing the necessity of learning by heart. Plato's warning about the consequences of writing for human memory is an important lesson for contemporary discussions around human enhancement through technology. New technologies, from mechanical looms to automatic cars, are always double-edged, extending certain powers while eroding traditional skills.

So is there anything special about enhancement of the human body that goes significantly beyond mere tool use? Is there any hope for our cyborg brethren to become a regular feature in our supermarkets, yoga classes and crèches?

Any compelling reason to implant chips in our brains and limbs through surgery and risk all the messy hardware updates and unpleasant maintenance issues that come along for the ride? Can we still expect superpowers for our physical bodies, and look forward to the ability to see ultraviolet light like bees or to have canine powers of hearing and smell? Or does the future instead lie in "downloading our brains" to computers, effectively trading in our fragile flesh for more durable hardware, as imagined in Ray Kurzweil's vision of the "singularity", a neo-Cartesian negation of the body and all its fluids and leaky orifices? Stelarc's Prosthetic Head, a simulated intelligence rather than a downloaded brain, is an experiment in what it might be like to live in Kurzweil's world, a Turing Test on humans.

Interestingly it is those individuals traditionally classified as "disabled" who are currently at the vanguard of human enhancement technologies. From cochlear implants and artificial hearts to neuro-prosthetics, these "early adopters" of assistive technologies are pioneers inhabiting an increasingly narrow boundary between a perceived "lack" and an unfair advantage in relation to the general population.

Consider South African athlete Oscar Pistorius, born with the congenital absence of the fibula from both legs, with his prosthetic blade "cheetah" legs leading to his near miss from participation in the Beijing Olympics. MIT researcher Hugh Herr has suggested that we may soon require an "Extra Special Olympics" to accommodate athletes with prosthetics and other enhancements. Perhaps in this context "non-enhanced" athletes would be regarded with something of the polite nostalgia with which we now view "real tennis" with its quaint long trousers and wooden racquets.

Or consider athlete and model Aimee Mullins who has redefined our notions of female beauty, with 12 sets of prosthetic legs for different occasions and her prominent appearance in Matthew Barney's celebrated Cremaster exhibition at the Guggenheim Museum in New York.

Beyond the glamour of the Guggenheim and the Olympics, a key driver in the development of new prosthetic and robotic technologies is the military, fuelled in the US particularly by demand from increasing numbers of veteran amputees from the Iraq and Afghanistan wars. Much of the media discussion around the Defense Advanced Research Projects Agency (Darpa) and human enhancement is focussed on notions of the 'future soldier', the cyborg in combat, but the thrust of much of Darpa's work in this area appears to be in allowing war veterans who are amputees to live relatively normal lives. The Darpa Revolutionising Prosthetics programme had aimed to have fully functional neural prosthetics controlled by brain-computer interface by the end of 2010, but ran into serious problems in integrating human neural pathways with control technologies. Darpa believe that brain implants – "implanted cortical microelectrodes" – should be the basis of future control over prosthetics, raising the familiar spectres of infection risk, and ease of maintenance and replacement.

Kazuo Ishiguro's novel Never Let Me Go, recently made into a major film directed by Mark Romanek, imagines a society where clones are bred and housed in a traditional English boarding school to grow replacement organs for their "originals" to permit the extension of life beyond organ failure. Ishiguro's novel and the film it inspired are a poignant alert to the potential societal costs of human enhancement and life extension.

New reproductive technologies and personalised genetic data provided by companies such as 23andMe are already requiring a dramatic reconfiguration of our conceptions of the family and courtship strategies. Personalised genetic screening, Gattaca style, could soon become intertwined with everything from bank loans and online dating to health insurance premiums, and we are excited to include in HUMAN+ a live experiment on the D4 Dopamine receptor gene which allegedly codes for "high risk behaviour" with the help of Dr Aoife McLysaght, Dr Ross McManus, Prof Fiona Newell, Prof Hugh Garavan, Prof Luke O'Neill and Prof Ken Wolfe.

The Methuselah Foundation has recently launched the New Organ Prize, "awarding as much as $10m to develop and transplant a new organ by the year 2020". The goal of the prize is to stimulate new techniques to grow and replace organs (kidney, liver, heart, lung, pancreas) from a patient's own cells. The same foundation also offers the M-Prize, awarded for the world record for the oldest-ever mouse. This ancient rodent will, it is hoped, lead to new ways to extend human life.

The quest to extend life and youth has become a central focus of the Transhumanist movement, championed by prominent figures like Aubrey de Grey. Life-extension through medical technologies, reduction in violence and improved diet is already a reality in the world. Even in the last forty years in Ireland our life expectancy has increased by a decade. The cryonics industry is fuelled by the enticing possibility of resurrecting the body through future technology, with companies offering to preserve your cryonically frozen head or full body through taking over your life insurance policy. Juan Enriquez of Biotechonomy is a strong advocate of the potential of stem-cell technologies, pointing out that we can already create replacement molars, bladders, ears and even tracheae in vitro.

In tones disturbingly reminiscent of Nietzsche's announcement of the Übermensch, Enriquez talks about the coming rise of Homo evolutis. Unlike Homo sapiens, Homo evolutis is characterised by taking direct and deliberate control of our biological destiny. Eduardo Kac's Edunia provides a contrary riff on human biological potential, combining the artist's DNA with that of a Petunia plant to create a new human-plant hybrid that extends the artist's presence and confronts us with the possibility of very different genetic futures.

A problem with the utopian perspectives of Enriquez and the Transhumanists towards the indefinite extension of life through regenerative medicine is that they tend to ignore on the one hand the social and emotional consequences of extreme longevity, and on the other hand to consider self-directed human evolution in splendid isolation from our changing ecological and environmental contexts. Some of the works exhibited in HUMAN+ highlight the issues inherent in life-extension. Euthanasia Coaster by Julijonas Urbonas is designed to deal with the ultimate boredom of longevity by allowing people to leave life in a euphoric state through an amusement park ride designed to kill.

Other works explore the fact that we may not be the ones who actually get to decide what new functions future humans need to perform. Laura Allcorn's Human Pollination Project demonstrates how much we rely on the ecosystem services provided by honeybees, and asks us to imagine a future where human behaviour has to be modified to provide pollination services due to the dramatic decline in bee populations. Zbigniew Oksiuta's Personal Biosphere is a meditation on the requirements for life and an externalised body providing our living requirements. Dunne and Raby's Foragers project considers a future society where food is scarce due to overpopulation and people need to create externalised stomachs so they can digest pond algae. John Isaac's disturbing sculpture If Not Now Then When offers a very different dystopian vision of the future of the human species, almost a Homo devolutis.

HUMAN+ is a combination of a sweet shop and a pharmacy, an Alice-in-Wonderland world of pills, promises and prosthetics. These works are ultimately about the fragile and contingent nature of human futures, they invite you to ponder the different dimensions, costs and unintended consequences of enhancement.

I am hugely grateful to my fellow curators and advisors for all their help and enthusiasm in creating this exhibition, to the Wellcome Trust for their support and encouragement, to Trinity College Dublin School of Medicine and the Trinity Long Room Hub for their support and advice and to all of our other supporters and sponsors, with a special word of thanks to researcher and designer Cathrine Kramer for helping draw together the cat's cradle of threads that link the ideas, artworks and experiments in the exhibition. Thank you, as always, to the Science Gallery team.

HUMAN+ tests our boundaries – boundaries of the body, boundaries of the species, boundaries of what is socially and ethically acceptable. Should we enhance ourselves, or seek to modify our descendants? Are we approaching a singularity of human-machine hybridization or de-skilling ourselves through our ever-increasing reliance on technological extensions of the body? Is extended human longevity a wonderful aspiration or a dire prospect for the planet? The ultimate decision is yours. Which enhancement will you choose?

Michael John Gorman is director of the Science Gallery, Trinity College Dublin. His essay from the catalogue of HUMAN+, which runs until 24 June, is reproduced here with the kind permission of the gallery