"When Zeus decided to end the Bronze Age with the great deluge, Deucalion and his wife, Pyrrha, were the only survivors. Even though he was imprisoned, Prometheus who could see the future and had foreseen the coming of this flood told his son, Deucalion, to build an ark and, thus, they survived. During the flood, they landed on Mount Parnassus, the only place spared by the flood.
Once the deluge was over and the couple were on land again, Deucalion consulted an oracle of Themis about how to repopulate the earth. He was told to throw the bones of his mother behind his shoulder. Deucalion and Pyrrha understood the "mother" to be Gaia, the mother of all living things, and the "bones" to be rocks. They threw the rocks behind their shoulders, which soon began to lose their hardness and change form. Their mass grew greater, and the beginnings of human form emerged. The parts that were soft and moist became skin, the veins of the rock became people's veins, and the hardest parts of the rocks became bones. The stones thrown by Pyrrha became women; those thrown by Deucalion became men."
-from the Wiki