I believe the number to look at would be 10,000 BC. That's around the time humans settled down, and there have been various human settlements and pottery found

I believe the number to look at would be 10,000 BC. That's around the time humans settled down, and there have been various human settlements and pottery found since then. I believe the number of ~5,000 years ago is just based on the records we have-- that's when the Sumerians come into the archeological record with complex artifacts. And of course that's when we have records of large civilizations like Akkad. But humans were certainly sophisticated long before then, even if they didn't have complex writing and government. One of the strangest pieces of archeology to me is the Löwenmensch figurine or Lion-Man, an ivory figure dating to 40,000 bc. So humans definitely had some complex culture for a long time. One theory I heard about why civilization developed so recently, is that it's in the past 10,000 years that the planet warmed up enough that farming became practical. I don't know enough about geological history to confirm that, but it seems like an appealing theory https://en.m.wikipedia.org/wiki/Lion-man https://en.m.wikipedia.org/wiki/Lion-man