Nothing happened. Prior to that we were mobile hunter-gatherers in very small groups. Hard to get an archeological reading from that. It is not that somethin

Nothing happened. Prior to that we were mobile hunter-gatherers in very small groups. Hard to get an archeological reading from that. It is not that something happened 6,000 years (actually more like 10,000 years) ago, it is that we left no easily-found trace before then. If you're interested, Guns, Germs & Steel goes into a lot more detail.