One Saturday morning in January 1982, Hugh Herr and Jeff Batzer set out to climb Mount Washington, the highest peak in the Northeastern United States at 6,288 feet.
To even the most dedicated climbing aficionados, it appeared a foolhardy mission. Avalanche conditions had swept through every gully on the mountain except for one, but Herr, 17, was well known for his fearless spirit.
A climbing prodigy who scaled the face of Mount Temple, a 11,627- foot peak in the Canadian Rockies at the age of eight, Herr had even begun free climbing without ropes in his early teens. Such was his reputation that Batzer, despite being three years his senior, trusted him implicitly.
But 1,000 feet from the summit, things would start to go very wrong. With winds reaching almost 100 MPH and visibility no more than a few feet, the pair were forced to seek shelter on the Great Gulf, an exposed glacial cirque on the mountain's north face. With no way up or down, they were trapped for three nights, exposed to the full force of the elements. By the time a search party found them, both were close to death.
Herr's legs were severely frostbitten. After seven surgical attempts to repair the circulation, doctors informed him that they had no choice but to amputate both limbs below the knee.
"In 100 years time, physical disability as a concept will cease to exist."
"As a double amputee back then, you were regarded as almost worthless by society," Herr said. "Someone spoke to my father shortly after my legs were amputated and asked, 'Is Hugh married?' And my father was slightly confused and replied, 'No.' And they replied, 'Oh good, thank god,' as if I'd become subhuman and how horrific it would be to be married to me as a cripple."
Far from being crippled, Herr would soon climb again, faster, higher, and better than before.
Over the past two decades, as a researcher and professor at MIT, Herr became one of the world's leading pioneers of bionic, "thinking" limbs—prosthetics embedded with machine intelligence that may become more agile, mobile and useful than their biological equivalent. Herr believes that they will eventually change the way the entire human race moves, travels and even looks.
Ten years ago, these ideas were the realm of sci-fi films. To most of us they still seem barely conceivable, more Iron Man than everyday life. But in a few select human test subjects around the world, they are rapidly becoming reality.
Artificial intelligence today falls far short of mirroring the complexities of the human brain which contains approximately 1 billion neurons, with around a trillion connections between them all. So far the closest we've come to replicating that in any shape or form is the OpenWorm project, in which researchers created a computer simulation of the 302 neurons found in a roundworm, and used this model worm brain to power a Lego robot.
Recreating human-like intelligence or even consciousness on a computer remains elusive, but what we do have available has begun to transform the lives of many amputees.
Forty-eight-year old Gummi Olafsson acts as a test pilot for Icelandic company Ossur, one of the world's leaders in prosthetics research. At the age of just nine he was struck by an oil truck. After over 50 operations, he eventually opted for a lower leg amputation. "I had been in pain for 28 years," he said.
Since his amputation, Olafsson has been wearing a bionic leg programmed with a kind of artificial intelligence that allows the limb to learn and adapt to his body.
Such bionic limbs and joints contain onboard computers which can sense the environment and flex the knee or adjust the ankle angle to match different terrain. They learn their wearer's unique gait within 15 steps, adapting leg swing and speed to the individual's natural walking pattern, and continue to adjust over time. The learning algorithms also automatically add power to the joints to make it easier when the wearer climbs stairs, and they can even sense when the wearer is becoming tired, adding additional strength and stability.
These bionic limbs have become so advanced that many believe they will start to become superior to their biological equivalents within the next five years.
"In the future exoskeleton devices will augment our movement so it's possible for anyone to run 100 miles over any sort of terrain without ever getting out of breath."
"In five years time, the artificial intelligence behind bionic legs will be able to actually take over the balance of the wearer, redistribute their weight and ensure that you have constant stability," Herr says. "So even on slippery or uneven surfaces, you will never fall."
It's a vast contrast to conventional mechanical prosthetic limbs which lack flexibility and any form of adaptability, which is thought to be the source of much of the chronic joint pain suffered by up to 70 percent of amputees. While there are still too few individuals with artificial intelligence-enhanced bionic limbs to make any conclusions, it is hoped that the technology will make such chronic pain a thing of the past.
And this is just the start. Intelligent prosthetics are being developed that can sync directly with the human nervous system, enabling the wearer to once again control their limbs with their own mind.
"In 100 years time, physical disability as a concept will cease to exist," Herr said. Having experienced and suffered from the stigma associated with disability during his youth, he has dedicated his entire research career to eliminating it. He dislikes the term "disabled," preferring to say, "people with unusual bodies or minds."
At MIT, Reykjavik and a handful of other locations around the world, scientists are experimenting with connecting prosthetic limbs to the nerves in human arms or legs. By measuring the electrical pulses in the muscles, the artificial intelligence inside the device is able to interpret what the brain wants to do and act accordingly.
Last year Olafsson upgraded his prosthetic leg to one of the new devices. For the first time in 11 years, he was able to directly move his lower leg by the power of thought.
"It was a surreal moment for me, just being able to roll my ankle around, and know that it was me wanting to do that, not the foot adjusting on its own," he said. "It's no longer the device controlling me, I'm in charge, and that's such an overwhelming feeling."
Herr believes that by 2050, methods of directly connecting a bionic device to the nervous system will be so advanced that amputees will be able to actually feel to some extent through their artificial limbs.
Many may be uncomfortable about the idea of future humans augmented with intelligent bionic devices that can take over decision making at any time
But such neurological experiments are not without risks. Many involve lengthy operations, implanting electrodes in the subject's brain or harvesting tissue from nerve-dense parts of the body so there are sufficient nerve fibres in the region where the bionic device is being attached.
"The individuals who agree to test these technologies are the astronauts of the future, allowing us to perfect these systems and making them safe," Herr said. "Ultimately all of humanity will owe them a debt as bionic technology is exploited in the coming decades and centuries to expand human cognition, sensory experience, physicality, and human expression itself."
However, when the methods require major surgery, some experts in bionics fear the costs could keep them inaccessible to many of the millions who could benefit. But there will be alternatives.
Over the past four years, California-based company Ekso Bionics has been developing non-invasive exoskeletons designed for patients who have lost motor function due to neurological damage.
These exoskeletons are wearable bionic suits that can substitute neuromuscular function. The artificial intelligence behind the suit adapts to the patient's weight and size, and controls their limbs, enabling them to walk again and learning a symmetrical gait pattern.
But as well as providing a life-changing and more affordable option for individuals with severe disabilities, Herr believes that they could make bionics mainstream for everyone, augmenting the capabilities of the human body beyond our natural biological limitations. From his own experiences as a climber, he says the transition from bionic devices being used purely by the disabled, to increasing numbers of able-bodied individuals, is likely to be driven by one of the strongest human emotions: jealousy.
"In the future exoskeleton devices will augment our movement so it's possible for anyone to run 100 miles over any sort of terrain without ever getting out of breath. And when people see individuals they have previous considered as inferior with advantages to them, that causes an interesting psychological shift. They too want those advantages."
When Herr began climbing again with his own specially designed prosthetic legs just a year after his accident, he soon surpassed his previous ability. While some members of the climbing community celebrated his new feats, others who had once pitied him accused him of cheating.
"It's part of the human psyche," Herr explains. "When we're certain that a difference causes inferiority, we're OK with it, we pity it and we condescend. As soon as the difference becomes equal or superior, then suddenly it's threatening."
As bionic devices and exoskeletons allow us to move in ways than we would never have previously thought possible, Herr believes increasing numbers of people will become open to the idea of augmenting their bodies with bionic technology and it will eventually completely change the way we look.
"Looking far into the future, in 100 years I think it will be difficult to recognise humans as they are today," he said. "It will be possible to use technology to sculpt the human body in any form that we want. I see that as exciting because our idea of beauty today is very narrow. But in the future there will be an exploration of human beauty and machine beauty on very different levels or forms."
But we are almost certainly going to be faced with ethical dilemmas. Herr describes a potential scenario where a 60-year-old man with painful, arthritic hands can either suffer on, or get them amputated and replaced with bionic hands which are as good as when he was 18. He argues that in this context, the latter would be the rational decision, an idea that many today may find rather uncomfortable.
"We're squeamish about these questions today because we view bionic structures as rather less human than our own bodies," he said. "But I believe this distinction will slowly dissipate. Eventually we will be able to 3D print bionics of any design and the built world will seamlessly integrate with our cells and tissues."
Last October Stephen Hawking had bleak predictions for our ability to coexist with intelligent machines. "A superintelligent AI will be extremely good at accomplishing its goals, and if those goals aren't aligned with ours, we're in trouble," he warned.
With that in mind, many may be uncomfortable about the idea of future humans augmented with intelligent bionic devices that can take over decision making at any time.
But before we find ourselves imagining post-apocalyptic _Matrix_-like scenarios, Herr points out that we are always going to be in charge of determining just how intelligent our devices can become.
"There could be many benefits," he says. "The machine can see things I can't see. As I step into the street, maybe I didn't see a car and the artificial system sees the danger and can push me out of the way. We view robots as potentially scary for humanity, but just how scary they are depends on us. They can be expanding, positive and enhancing to humanity."
Herr knows this more than most. Thirty-four years on from an accident which many assumed would end his life as he knew it, his bionic enhancements enable him to climb with the same daredevil abandon as before, scaling 1000-foot walls high in the Italian Alps.
During that time, he's experienced an extraordinary change in public perceptions and attitudes towards what's possible with prosthetic limbs. "Last April, I was at Boston airport wearing shorts and bionic legs, and I think four people came up to me and said, 'Did you run the marathon?' Even 10 years ago, nobody would have associated an amputee with marathon running, but now people see bionic legs and they probably assumed I ran it and ran it very fast."