I have no idea why you think 2,000 BC has any special significance. Man has ALWAYS had religion.Natural ethics is something that is the same amongst all of us. 99.9% of us. What is right, is right. What is wrong is wrong.We don't need a religion to tell us that, because we never would have made it to 2000 BC without it.Lots of wishful thinking but little grasp of reality. Religions are very real and most people in the world would agree. The ethics of religions reflect the ethics of man, in other words they are all over the place and people tend to find the religion/sect/denomination/cult/etc. that best reflects their ethics. I'm not sure what 'natural' ethics are but they would have to include the cooperation of bees and the infanticide of lions.But ethics are real, and religions are not. Religion's ethics are evil. True natural ethics are real and part of evolution. Every species has it.
Only humans kill each other over religion. It's a money and power-making scheme.
It's just natural.
But what started happening circa 2000 BC, is that they invented "religion". And suddenly our ethics changed. No longer was it about the greater good of humanity, but it became the greater good of the religious ruler.
Shit went downhill from there.
As far as ethics and religion, you have it backwards, religions don't dictate the ethics of the society, they reflect those ethics. That is why the OT is so different from the NT, the society of the Jews changed when they went from a conquerors to conquered.