And that coincided with a warming climate,
which certainly was part of the necessary conditions for it.
But then, all the fascinating question is,
why would people settle down and start farming?
And we've always described it in terms of progress.
Well, of course, anybody would farm once they had the idea.
[LAUGH] But now, historians are beginning to see that life was much easier under
hunting and gathering for most people and that farming involves a lot more work.
That people wouldn't really necessarily choose unless they had to.
So now we're beginning to analyze the reasons why they had to do that.
Stable food supply.
>> Rising population, so there are not as many places to move to,
a declining wild animal population, and a warming climate that made it possible.
>> And they came to thee river valleys, right, for
these early civilizations as they emerged.
>> Right, although the first agriculture, apparently, was practiced in higher,
cooler altitudes.
But then as the climate dried, and heated up and
dried, people were driven into the river valleys.
>> So we've got Mesopotamia and the Nile, and
the Indus Valley, the Chinese Yellow River.
>> And then later, of course, in the Americas,
there are not river valleys in the Central America and in the Andes.
>> So these are the rise of these major civilizations, and
again you'd date them from when?
>> About 3500 BCE.
And, of course, the really fascinating thing is that they arose independently as
far as we can tell in at least five or six areas around the world.
More or less simultaneously, although the Americans were a little later.
>> And they required sophistication of organization and so on?
>> Exactly, well then you get into what really defines a civilization.
And certainly they're much denser populations.
They're specialized occupations.
They're much more complex organizations.
They have tribute that's collected by force if necessary,
that's one of their chief features.
And they have much more energy flowing through the system than earlier.
>> Material energy and trade and >> Right, but not only material energy,
actually natural, I mean, energy, which includes food stuffs and
trade and all of these, so that many of the big historians are seeing
the defining pattern to big history as increasing complexity.
And then complexity they're defining as the amount of energy
that flows through mass or matter.
And, plus, the number of combinations there are.
So they're actually trying to measure this increasing complexity.
>> Which is true for the whole universe system.
>> Exactly. >> You're saying,
we're seeing it especially as civilization emerges, too.
>> So it's part of a bigger pattern.