How much can one person do?

This same question can mean lots of things, many of them containing far more nobility than the one I am actually asking.  But never-the-less, I'll admit that I've been contemplating this less meaningful version for some time as I muddle through my own training and mull over my own endurance ambitions. The pursuit of what can be thought of as 'peak' achievements in the world of endurance sports consumes many of the people who enter into this strange and hard to understand (for those not directly involved) world.  Running 100 miles.  Racing for days.  Riding for centuries.  Men and women have demonstrated that human potential is something to be in awe of--the mind and body, under the right circumstances can do seemingly impossible things.  Passion, dedication to one's craft, disciplined training, and will-power applied over decades--combined with science and a loss of the more 'obvious' challenges that unexplored places once offered--have pushed people to incredible heights.  'Peak' events in each major discipline--races or efforts hard and long enough to make a bucket list for all but the most dedicated participants have gotten exponentially harder than they were a generation ago.  These events are now becoming commonplace, routinely reaching their participant limits within hours of registration opening. 

There is no doubt that the world of the ultra-endurance athlete is no longer a lonely place as it once was.

But it is still, at least to my knowledge, a pretty segmented one.  And this, is where my fascination lies.  Is one person capable of achieving success in ultra-endurance across disciplines?  Is it humanly possible to develop one's abilities to compete in say a 100 mile paddle race and a 135 mile winter bike race?  Would any of the folks bold enough to sign up for a 100 mile trail run even consider also signing up for END-WET, our 36 mile swim?  When we put out our Undead Hall of Fame challenge last year, over 30 athletes answered the call and attempted to bike 100 miles of singletrack (in 12 hours) on Saturday and then run 50 miles (also in 12 hours) only half a day later.  Only four were able to do it, and of those, only one might possibly hope to finish the swim.  What kind of person would it take to be able to perform at such an impressive level, over such a broad spectrum of disciplines, within a narrow time window?  Just how much can one person do?

I'm not sure yet how or when this question will be answered, but I'm hoping to play a part in the inquiry (not as a participant mind you, but as an event director!).  And while the question (as I ask it) might not inspire world peace, seeking the answer will certainly keep me inspired here in my piece of the world.