"Let us make man in our image, after our likeness" — the creation language this genealogy deliberately echoes, after the fall.
Luke 3:38 runs its genealogy all the way back to this same source, naming Adam himself "the son of God" - the divine likeness this chapter opened with, still on the record generations later.
This is the book of the generations of Adam. In the day that God created man, he made him in God’s likeness.
God said, “Let us make man in our image, after our likeness: and let them have dominion over the fish of the sea, and over the birds of the sky, and over the livestock, and over all the earth, and over every creeping thing that creeps on the earth.”
the son of Enos, the son of Seth, the son of Adam, the son of God.
This heading — "the book of the history of Adam" — opens a section that Cassuto argues runs all the way through 6:8, not just to the end of this chapter. The evidence: 6:8's closing line, "Noah found favor in the eyes of the LORD," deliberately echoes this opening's own language ("God created man... and blessed them"), and the next new heading doesn't appear until 6:9's "the history of Noah." The whole genealogy, in other words, is bracketed on purpose — creation and blessing on one end, favor on the other.