Searching for "stem cells" or "stem cell" on Scirus returns 995,702 results, of which 152,648 are journal publications with the term in the title, abstract or contents, and 62,220 patents. According to Wikipedia, Stem cells were postulated in the early 1960s and shown to exist in 1963, giving us a 40-year window to chart the progress of human knowledge. However, looking at Scirus, I find articles as early as 1916 that seem relevant, and a patent in 1947 that also looks relevant to a layman.
Starting in 1960 excludes 74 journal articles and 2 patents, so we will make that our base year. That gives us a Compound Annual Growth Rate (CAGR) of 16.63%, or enough to double human knowledge about stem cells every five years. Hooray! We have another winner. That actually would double every 4.5 years. For patents, the CAGR is higher, 26.47%, which would double every 2.95 years. (Just for fun, if I used a base year of 1947, when the first patent was filed, the CAGR is still enough to double human knowledge every five years, although it drops to 20.2%).
Perhaps the most important finding is that President Bush's restrictions on stem-cell work in the U.S.A. has not dragged progress down, with over 100,000 journal publications and over 56,000 patents filed since he took office. Of course, I'm not counting how many of each are American, but that's for domestic policy wonks to debate... or even research, if they have the time.
As in some (not all) other sectors, we see that the quickest growth for academic publications is early, while patents explode just about the time that growth slows in academia. I'm not sure that's a coincidence...
Again, we see that when the incentives are properly allocated, we can double human knowledge in a sector every five years.
Click to see the figures below.