Other peoples ideas

I was thinking today about the development of new ideas. How much of what we actually write is new and how much has been done before?
Furthermore how much of what we do is groundbreaking and how much is a development of ideas already thought of.

These thoughts have been due to a number of this, I've been reading Bill Bysons "A Short History of Nearly Everything" and the majority of the individuals with scientific groundbreaking discoveries were not the initial discovers. Often enough, the discovery had been made many years previously and additional work done on it had brought the discovery to the limelight.
Of course as with everything there are exceptions to this, specifically Einsteins theory of general relativity which "many physicists believe that without Einstein, it could have been another few decades or more before another physicist worked out the concepts and mathematics of general relativity".

The other reasons for these thoughts are the nobel prizes which are being awarded at the moment. What does it take to get a nobel prize and for the person who wins the prize, how many other peoples ideas were used to arrived at that point?

I think in the end we'll find that everything is linked, nothing is original but every new step is original. A bit like in nature where everything evolves from one thing to the other, our ideas evolve, just at a much faster rate.