Adam and Eve sinned by eating of the forbidden fruit of the tree of knowledge of good and evil (Gen 3:1-19).  By this time evil was already at work in the spirit world because Satan, in the form of a serpent, seduced Eve into disobeying God (Gen 3:1-5).  He sowed seeds of doubt regarding what God said (Gen 3:1), he lied about the consequences of disobedience (Gen 3:4) and he promised things that would not materialize (Gen 3:5).  He still works in this way today, lying (John 8:44) and trying to deceive believers (2 Cor 11:13-15), and doing all he can to destroy the effectiveness of believers (John 10:10).  This act of disobedience by Adam and Eve put all of mankind in a state of sin (Rom 1:18-3:20; 5:8; 1 Cor 15:21).  The unsaved, or natural man, is a slave to sin (John 8:34).  Each person is guilty before God (Rom 3:19) regardless of his nationality, upbringing or religious heritage.