Not sure. Genesis doesn’t make it clear to me either but I find the topic interesting. For example. What is the mark of Cane? Do you know that in middle evil times, witches would be searched for a certain mark, when they made a pact with the Devil? If a mark exists to separate the line of Zeph & the line of Cane, why would God encourage us to mingle our seed?

Also, we don’t know much about the pre-deluvian world; all Gensis tells us is that Noah was 10 generation separated from Adam but the world had become corrupted by then. I would also like to know more about that era. I got more questions than answers, homie.