Actually, what I suspect it is is the corruption or pollution of the human genome with foreign DNA, whatever the source.
When Scripture tells us that Noah was blameless in his generations, the Hebrew word *tamim* means *complete or sound*.
Could be that it is referring to PHYSICAL soundness or completeness.
Just a thought. I had heard it long ago, and I don’t remember where, but it does make sense, so I never dismissed it off the cuff.
I believe that is EXACTLY what it refers to. Noah was righteous spiritually, but also physically. He was not stained by the scourge of the Nephilim. The implication is, that everyone else on earth WAS. How many people were on the earth at the time? Possibly billions. They came within an eyelash of succeeding.
The pre Flood world, was as different as night and day, to the post Flood world. Noah and his family, were the only ones who ever saw both. It must have been a bit of a traumatic experience for them. 😁