I believe two major factors contribute to the enormous innovation that we have seen over the past hundred years. The first major factor is child rearing; the second major factor is automation of information processing. If you think about it these two factors are the two most retarded in the history of humankind up until the turn of the previous century.
We have been making, storing, and otherwise producing prodigious amounts of information for well over three thousand years; we obtained the ability to actually search, sort, process, and transmit major portions of this body of information only recently within the context of human history.
More importantly, child rearing has been particularly effective at causing social driven innovation. It makes sense in the context of facilitating talents, skills, and knowledges that improving how we raise our children will have a direct and dramatic effect on the rate at which we advance (changing the rate of change). I could try to explain the exact mechanics of this but many have written far more detailed accounts than I have, so I would suggest reading Lloyd deMause's "Foundations of Psychohistory" or "The Emotional Life of Nations."
Disclaimer: deMause's works contain information that maybe inappropiate, uncomfortable, or offensive for some readers.