I finally picked up a copy of Guns, Germs, and Steel. I've heard good things about it, but I'd never read it. I'm still only partway through, so I may misrepresent him.
For over a decade, my theory on the success or failure of civilization has revolved around population density. His theory pretty much matches mine. He talks about "population" rather than "population density", but I think he agrees that ten thousand people in a hundred square miles will "advance" faster than ten thousand people in ten thousand square miles (which is actually quite a high population density for a hunter-gatherer population).
Both of our theories (which, as I mentioned, appear very similar) revolve around the idea that a higher population density results in more specialization, which drives civilization. For example, hunter-gatherer tribes didn't have politicians, didn't have writing, and didn't have farming. A city-based population will have not only all three of those, but also armies, currency, and law.
Of course, population density is largely created by having MORE FOOD. It also enables us to be more efficient at producing food, which in turn generally causes higher population density, etc, etc.
To me, the important thing is the extra humans. In a tribe, you don't have any extra humans. They're all hunters, gatherers, shamans. Only the occasional disabled is "extra". However, as population density rises, efficiency rises. Wealth is generated. Suddenly, you've got someone like me. I do NOTHING critical to survival. Not a single solitary thing. But I do advance civilization, in my own small way.
To me, the population density is only important because it provides all these extra humans who have to figure out a way to buy all the stuff they need to survive. According to my mostly-unrelated theories, that need to buy is the important part. If it came free, those extra humans are not driven to advance the society and therefore don't really count towards our needs.
"Why is he harping on this?" you hopefully say.
Because extra humans are only as powerful as they are connected to civilization. If an extra human is connected to a million people, he can innovate from their collected history and needs. If that extra human is connected to a BILLION people, suddenly his scope is much wider and the chances he can find a better way to buy his stuff is correspondingly higher.
If you didn't get that, or disagree with it, I probably didn't communicate right. I'm saying: You only have as many opportunities as you can find. If you're connected in fewer ways, there are fewer opportunities.
Take a look. The mightiest historical empires were known for their what? If you answered anything related to "connectivity", you win! Roads! Standardized coin! Shipping lanes! These are the things empires were built from.
Hi! I never would have met you if not for the internet.
Nice to see you. Nice to know we're connected.
Our population density has gone from being people per square mile to people per web visit. The number of extra humans is immense, well-connected, and growing exponentially more effective every year.
Where is the next cradle of civilization? China? India? America? No.