> Is it that there's been a fall in the rate of innovation or a massive
> rise in population?
I thought the same. He should have looked at absolute numbers of 'innovations'. An advance in knowledge isn't a resource like grain or steel that needs to increase with population growth, it is theoretically an unlimited resource in that one person's use of the knowledge doesn't deny another the ability to use that same knolwedge (understood that people who fight FOR copyright do try to create a zero sum game out of knowledge).
Plus, even if you want to take population into account, you would have to look at growth in numbers of educated populations, not population growth in general, being that they are the ones who are going to create the lionshare of scientific and technological innovation.