There are all sorts of reasons that human beings can increase knowledge (however we define that) through society. A huge one is division of labor; rather than everyone trying to make advances in medicine, physics, economics, etc., people specialize and this is far more productive.
But there's another aspect to it that I haven't seen stressed before. Let me illustrate it with a little thought experiment: Suppose Gene Callahan, me, and 98 other people with "deep thoughts" are locked in a room. (Let's hope it's a big room with plenty of toilets.) Now we want to come up with a way to leave the room after 2000 minutes, such that everyone is as smart as possible. Finally, suppose that in the beginning we are all equally knowledgeable and intelligent. (Yes, I shall be humble for this hypothetical scenario.)
As above, one way would be for each person just to think on his or her own for the allotted time. But suppose instead, each person picks a different problem, and then thinks about it for 1000 minutes with the goal of exploring different possible solutions, identifying "dead ends," and coming up with ways to best summarize these musings to everyone else in the room.
Then, in the remaining 1000 minutes, each of the 100 people gives a ten minute summary of his or her work to the group. In a sense, each speaker would be "saving" everyone else 1000 minutes of thought in exchange for listening 10 minutes. And notice that that isn't merely where the economies come in: it also has to do with the fact that each speaker is providing that "saving" for ninety-nine other people.
I think this captures (part of) what happens in the academic community. When a genius like Einstein "sees something," he publishes it and then everybody else can start working on problems with the new head start. General relativity isn't that intrinsically difficult; by now undergrads at good schools can learn it.
This is even more apparent in philosophy and economics. When somebody dreams up a great argument (e.g. Bastiat's "Petition of the Candlemakers"), it frees up everybody else's time; they don't have to agonize over the complicated issue so much when someone makes it crystal clear. So somebody like Mises doesn't need to worry about free trade; he can go ahead and solve the problem of the subjective valuation of money units.