The human population very suddenly saw a flux, consuming everything in its path. Prior to this, everything was provided for humanity through the environment they'd been born into. While there was hardship, it was nothing on the scale of where humanity had found itself now.
Groups formed as the Earth dried up. Foraging was no longer sufficient. But, rapidly humans learned how to plant their own food and maintain livestock. But the numbers just kept increasing and so too did the science and practice of agriculture. And with agriculture came the notion of ownership. If you were to fuss over a crop for months at a time in order to yield its rewards, it was unreasonable that someone else could partake of YOUR crop. This is in contrast to the foraging human, that was merely fortunate to find sustenance that the Earth had provided for them.
With property came Hard Territory. Prior to this, there was a Soft Territory, which had more to do with the location of a grouping of humans. Hard Territory was the habit of owning a plot of land long-term. Not only would you own that plot of land for your entire life, you would try to pass the land on to your offspring. There was no flow to humanity in a collective. Instead, as the populations grew, there was dispersal and crystallization. Communities split and reconstituted in another plot of land that would accommodate their voracity.
With Hard Territory came conflict. If one human could own another object, then one human could take that object from another human and this became humanity's major preoccupation for... well, this maybe hasn't yet resolved. Ownership has obsessed the human consciousness. Owning things, places, even other people was admirable, but owning more was desirable and so humanity started to mar itself as empires raced to own more. To own everything. But this was not going to be tenable and the human brain responded.
In this era there was something being born in the human brain: God.