When the time came for Rebekah to give birth, there were twins in her womb.

A time to be born, and a time to die; a time to plant, and a time to uproot what was planted;

As when a pregnant woman gets ready to deliver and strains and cries out because of her labor pains, so were we because of you, O Lord.

Then she gave birth to his brother Abel. Abel took care of the flocks, while Cain cultivated the ground.