History is quite incomprehensible without giving a social context. Genghis Khan could have not conquered without the mongols being trained in hunting and herding, thus leading to the tactics that resulted in overwhelming victories.
Einstein could not have written the papers he did without the corpus of the scientific knowledge and the people around him. It was his will that drove him forwards but to truly undertsand his conditions better we need the historical context.
Maybe a stone age Einstein would have invented bronze. Who knows. But, theory of relativity even as a concept would have been beyond incomprehensible.
People do not exist in a vacuum. The social context is the ocean, the individual is the surfer on the waves. Individual impetus drives the person forwards but if the weather is not agreeable to his ambitions he cannot surf.
Evidence for the "in the air" version clearly exists in science and mathematics, where progress leads a certain direction, then a particular individual is the one who makes big advance or discovery. Often more than one person is independently making the same advance at the same time. Think of Newton and Leibniz, who independently and at same time developed calculus. Or Darwin and Alfred Russel Wallace, same thing with theory of evolution. All of these guys did extremely impressive things. But do you really think nobody else would have developed calculus or discovered evolution if these guys had all died in childbirth?
I'm not saying all advancements are 100% "in the air" and that individuals basically do nothing. But, certainly, for many of these individuals -- who we (rightfully) revere -- the same advancements (or discoveries, or destruction, or whatever) would have been accomplished by someone else if they had never been born.
If you're interested in a smarter man than me going on about this idea, I suggest you read the Foundation series by Issac Asimov.
EDIT
Scott Alexander covers that one too:
http://slatestarcodex.com/2013/03/07/we-wrestle-not-with-fle...