Genesis 9:20-27 describes the time when Noah became drunk and "lay uncovered inside his tent." Ham, one of his sons, "saw his father's nakedness and told his two brothers outside." Whatever this refers to, Noah considered Ham deserving of punishment. He cursed Canaan, Ham's son, while blessing Japheth and Shem. This had nothing to do with race, as some have suggested. Rather, Noah anticipated in Canaan the evil traits that characterized his father Ham.
