Simultaneously, I've been reading through the book of Genesis as well in the Jewish Study Bible. One thing is clear: the "genesis" is essentially a reference to all the known world's people in addition to the world itself.
One of the interesting things to see was the lineage of Cain and the lineage of Seth having extremely similar names, both ending with someone named "Lamech." The difference is that in Seth's lineage, Lamech is the father of Noah.
There are several possibilities of why the names are similar, and my own perspective is that Cain was probably originally seen as the ancestor of Noah with Seth being a later invention OR a different variation on the story of Adam and Eve's children altogether that was edited into the overall narrative.
Cain being Noah's ancestor then means humanity is descended from the first murderer as opposed to a neutral, seemingly righteous person.
On the other hand, since Noah's supposed to be the "new Adam" and the reboot of humanity as a whole, I'm not sure why the difference in lineage would be absolutely essential.
Things to ponder on!