Have people really changed since recorded history, or have they been bad all along. People have only been restrained from doing more evil than they have done throughout history, because humans have created God for people, and Laws for societies.
Even with these restraints in place, the people of the world have been and continue to be bad and without peace.
The bible contains accounts of mindless butchery and ethnic cleansing by both Israel, and their enemies the Assyrians and Babylonians.
Historians can also talk to us about psychopathic conquerors such as Alexander the Great and Genghis Khan. White Americans ethnically cleansed the Native Americans. Stalin killed a couple million more Russians than Hilter killed Jews.
More recently we see genocide in in Ruwanda, ethnic cleansing in the Balkans, terrorism in Afganistan.
So no when taken as a species, man has not changed.
The O.T. is a lot older than the Jews, and older than the writing system which first recorded it. Most of the pre-mosaic stories were passed down from gen to gen by word of mouth. It was only during and after Moses that these stories, already known to the Israelites, were written down. This is why the flood tale correlates to the Epic of Gilgamesh....because they are related.
I look to Sumeria, and realizing that there were others before them.
Ideas found in the Bible were largely borrowed from pre-existing peoples. The Levant is a major human migration superhighway, and has been since before civilization existed....many ideas have been left there and have found themselves reclothed into what we see as "Biblical" today.
Someone was living at Catal Hoyuk...and they had beliefs of their own.