some puzzles

From yesterday's reading in Genesis 6 this part didn't seem to fit: When human beings began to increase in number on the earth and daughters were born to them, 2 the sons of God saw that the daughters of humans were beautiful, and they married any of them they chose. 3 Then the Lord said, “My Spirit will not contend with[a] humans forever, for they are mortal[b]; their days will be a hundred and twenty years.” 4 The Nephilim were on the earth in those days—and also afterward—when the sons of God went to the daughters of humans and had children by them. They were the heroes of old, men of renown. Afterwards it goes on to talk about how the heart of man is full of evil, but these 2 passages don't seem to indicate it was the human fault, that it was external sources that were the evil ones. So that was a bit puzzling. From today's reading my puzzle is when Ham (apparently) sins against Noah, Noah curses his son Canaan. Why Canaan, who was only one of Ham's children. My ponderings for today!