When Zeus, king of the gods, decided it was time to end the Bronze Age of Man, he decided to flood the earth by creating the great deluge. Prometheus, father of Deucalion, had foreseen what was about to happen, so he warned his son to create an ark, in which he and his wife could find refuge. In the ark, Deucalion and Pyrrha survived the flood and were the only two people that survived. When the waters receded, the ark landed on Mount Parnassus, which was the only spot that was not destroyed by the waters.
Yet, Deucalion and Pyrrha had to repopulate the earth. So, Deucalion asked an oracle of the goddess Themis for advice, who told him to throw the bones of his mother behind his shoulder. Deucalion and Pyrrha believed that by "mother", the oracle meant Mother Gaea, and by "bones", it meant rocks. Deucalion and Pyrrha took some rocks and threw them behind their shoulder; as soon as the rocks touched the ground, they started changing shape and formed humans. The rocks Deucalion had thrown became men, while those thrown by Pyrrha became women.