As soon as Adam and Eve had kids and they were old enough to have sex with each other, those kids had more kids themselves so more brothers and sisters could have sex with each other. A practice that was carried on in ancient Egypt and still today in the backwoods of the USA.
After several generations they walked away from Eden real fast in small groups in every direction, some naked, some covered in fig leaves. The naked ones turned black under the sun and the others turned into Asians and Scandinavians, the short ones were told they had to be Pygmies and go to Africa. Others who drew the short straw were told to go live in the snow and ice of the north pole.
When the naked ones from the first Eden who became Aboriginals got to Indonesia they taught themselves to swim all the way to Australia and then they called a new place on the South Coast of NSW, Eden in honour of their first home.
Each small group was given a book about what culture and language they would have when they got to their new homes and that way it didn't take tens-of-thousands of years to develop cultures and language.
So you see there is absolutely no need to suspend one's disbelief. It all fits beautifully with the time line.
The only problem I have is that they all died anyway in the Flood. Imagine poor Noah and His family when their kids started popping out all colours and races to replace all them drowned ones. So humanity is really only about 3,000 years old. Still works for me.
