There is likewise no Scriptural evidence that Adam was not the first human.
You are simply reading into the text that Cain did not marry his sister.
And the people Cain feared would have been the numerous future generations,
for they lived for hundreds and hundreds of years during that time.
The bible states both:
"All the high mountains under the entire heavens were covered." (Ge 7:19)
"Pairs of all creatures that have the breath of life in them came to Noah and entered the ark." (Ge 7:15)
Noah didn't have to find 'em, nor round 'em up.
The ark was the length of 1 1/2 football fields, as wide as 3/4 of a football field, and as high as a four-story building.
It woulda' worked.
it does not require us to believe that there were no humans before Adam, or that the flood of Noah's time covered 30,000 foot mountains. I had long suspected this but could not properly explain it until I read Biblical Antiquities: Book I by archaeologist and Bible scholar E. Raymond Capt. As Capt explains, the key to understanding the creation story is to know that, unlike the rest of Genesis, it was recorded much earlier, and not in Hebrew, but on clay tablets in ancient cuneiform. When reading Genesis you will notice this, you will notice a brevity, and a style in the first few chapters that are not in the rest. There is more, much more to this, and it is very fascinating.