I think it's a sheer mass problem. In order to support a few million people full time innovating, you need a tremendous support infrastructure that just wasn't

I think it's a sheer mass problem. In order to support a few million people full time innovating, you need a tremendous support infrastructure that just wasn't even possible with ~10m people on the planet. http://www.gigamonkeys.com/flowers/ http://www.gigamonkeys.com/flowers/ is related - if you have a percentage of your population working on making the rest of the population more efficient, this only makes sense above a certain leverage level.