Tough question, there are theories that just wont die and are held as true today as they were when the said scientist proposed them, will they remain true who knows, but what in your opinion is the key development in human understanding. Who is the greatest in a Muhamid Ali style, in as much as you can say when the giants shoulders they are standing on are also pretty important. Who broke the mold, left the rest for dust, eclipsed the others in a blinding flash of inspiration.
