Ok, well....It took 12 years to go from 4:06 to sub-4, which is the same relative improvement needed here.
The problem is that training methods, technology, scientific understanding, incentive to perform, etc. are all lightyears ahead of the crude methods/science of the 50s. It, theoretically, could turn out that humans are training all wrong and have significant room for "natural" improvement. Obviously though the odds of that decrease with the increase in understanding and abundance of dedicated athletes.
The point about it being lowered rapidly is fool's evidence. It is being lowered rapidly because the last decade or so (less, really) is the first time in history that the world's best runners are running the marathon in their prime. No longer are 2:04-caliber guys running on the track until they inevitably lose a gear and move up to run a 2:08 marathon.
Barring pharmaceutical breakthroughs (possible) or a genetic freak beyond current comprehension (also possible, but unlikely given just how much better he'd have to be), sub-2 is decades away at the least
Me:
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