On September 2, 2010, Karen Throsby became the 1153rd person to swim the  English Channel, taking 16 hours and nine minutes, and keeping herself going on  handfuls of jelly babies.

Many Channel swimmers are purists: wetsuits are banned, never mind  performance-enhancing drugs. The sport sees itself as an assertion of human  ability in natural form. But Throsby, a sociologist researching the effects of  extreme sports, takes a different view.

She was a speaker at Human Limits, a Wellcome Collection symposium linked to  its Superhuman exhibition in London on physical and mental enhancement. The  question it investigated was how much technology can humans use before they  become something else — a cyborg, perhaps, or a superhuman, a post-human, or a  trans-human. What are our limits?

Some speakers discussed the “singularity”: the idea that in a few years’  time, we may converge with our technology to the point that some as-yet  inconceivable superhuman entity emerges.

Others highlighted the fear we can feel when new inventions threaten our  sense of who we are; uneasy about our authenticity, we look back nostalgically  to an era assumed to be more human.

Throsby’s contribution was to remind us that even something as apparently  basic as marathon swimming involves many artificial techniques: gaining weight,  acclimatising to the cold, monitoring one’s psychology, and developing new  micro-senses — an awareness of tiny differences in water temperature, a  heightened kinetic sense of the body’s balance and position, and so on.

It means self-transformation, and is filled with “uncountable, mundane bodily  technologies”. Channel swimmers use rubber caps, sunblock, Vaseline to prevent  chafing, sleek swimsuits, and energy-boosting snacks. They are accompanied by  boats with GPS.

And they use goggles, an invention variously attributed to Polynesians,  Persians and the Inuit, but later improved by innovators such as first female  Channel swimmer Gertrude Ederle, who smeared paraffin wax on motorcycle glasses  in 1926 to make them watertight. More recently, goggles have been made with  better rubber, adjustable straps, and prescription lenses. It would be hard to  swim far or fast without them.

As always, successful technologies tend to disappear in their use, becoming  almost indistinguishable from ourselves and our own efforts. A smartphone sits  in our hand announcing “I am technology”, but the spectacles through which we  peer at its screen and the pocket into which we slip it feel as natural as our  own hands and eyes. It takes a leap of thought to realise that Vaseline and  jelly babies are technology, too.

Human Limits asked how much technology we can add before losing ourselves,  but there is also the question of how human we remain if familiar enhancements  are taken away.

These could include both devices and practices — our mastery of writing, our  elaborate educations, our knives and fires and cooking-pots, our language, our  laboriously polished social skills. At what point do we cross the line into  being no longer ourselves?

As human beings, we tread a narrow ridge where we roughly know who we are — but the ridge does not run straight, or lead in a predefined direction. It is  partly up to us to decide what a human being is.

“Man is rightly called and judged a great miracle and a wonderful creature,”  wrote the philosopher Pico della Mirandola in 1486. He opined that we are  wonderful not because we live up with the angels, or down with more modest  beasts, but because we occupy an intermediate realm in which we invent and alter  ourselves.

“Neither a fixed abode nor a form that is thine alone nor any function  peculiar to thyself have we given thee,” he imagines God saying to man. “Thou,  constrained by no limits, shalt ordain for thyself the limits of thy  nature.”

Of course we are hemmed-in by mishaps and errors, and technology goes wrong.  But to a large extent we are our own works in progress. And when all goes  smoothly, we don’t even know it.