In a few verses the writer is able to convey a sense of the catastrophic descent of the human race from covering up killing to boasting in bloodletting. Cain’s nonchalant words and his great-great grandson’s boast frame this genealogy and mark its spirit and its descent into a moral and spiritual abyss. The irresponsible ‘Am I my brother’s keeper?’ attempts to deny murder (Gen. 4:9); ‘I have killed a man for wounding me’ glories in it (Gen. 4:23). This is certainly not the dominion intended for humanity in Genesis 1-2.
Stephen Dempster, Dominion and Dynasty, pages 70-71