Cain killed Able and had offspring to spread his DNA. Able, no so much so. Oh, and I need $100,000 in grant money for arriving at that conclusion.
This tendency is not specifically in our DNA. It’s spiritual in nature. That is why God described it as “sin” to Cain.
Unless I’m mistaken, it was Seth’s line that survived the Great Flood (through Noah and his sons) and not Cain’s.