Biblical
Adam and Eve had two sons. The first son was named Cain and the second son was named Abel. Cain grew up to become a farmer and Abel grew up to become a Shepard. Adam and Eve were asked to sacrifice a lamb for disobeying God and they told this story to Cain and Abel. Abel was very concerned that his sacrifice be special to God, so he offered him his first and best lamb. Cain offered the Lord his straw. The Lord respectably took Abel's offering and not Cain's. Cain became very jealous and angry with his brother, so Cain asked Abel to go for a walk and he struck his brother down and killed him. Cain then heard the Lord's voice asking where his brother is. Cain responds "I know not: Am I my brother's keeper?"