Humans Have Fallen Into Sin

As Adam and Eve had been warned to not eat of the forbidden fruit of the Tree of Knowledge of Good and Evil, sin was introduced into the entire human race when they disobeyed God.  They ate from the fruit because the serpent told Eve that by eating the fruit she would have the knowledge God has; the knowledge of good and evil.  By disobeying God who told them not to eat from this tree they went from not knowing good and evil to having their eyes opened to good and evil and so fell and were cast out of the Garden of Eden.