In the Hebrew scriptures, the sons of Adam and Eve .
According to Genesis , Cain, the firstborn, was a farmer, and his brother Abel was a shepherd. Cain was enraged when God preferred his brother's sacrifice of sheep to his own offering of grain, and he murdered Abel. When God asked where Abel was, Cain pretended ignorance, saying, "Am I my brother's keeper?" God punished Cain by sending him into exile but marked him with a sign as a warning to others, promising that he would be avenged if he were killed.