[evanwise]

The raw computing power of the human wetware has not increased appreciably over historical timescales, but the total intelligence of humanity, includes, for example, the increase in effective intelligence gained by storing knowledge in external devices like books. The gestalt organism that is "humanity" is much smarter than it was 500 or even 100 years ago, which correlates with our ability to extract resources. It's an extremely simplistic model, but since I was only after a very rough guess, I went with it.