Plato's Symposium uses the dialogue to expound various theories of love. Each participant by means of very personal contributions adds something towards an exposition of love that at the end receives its conclusion from Socrates. The comic playwright, Aristophanes's speech is an explanation of why people in love say they feel "whole" when they have found their love partner. He begins by explaining that people must understand human nature before they can interpret the origins of love and how it affects their own times.
Aristophanes says that in the beginning there were three parents: Sun, Moon, and Earth. Each produced an offspring, round and otherwise like itself. From sun was produced the man; from earth, the woman; from moon, the androgyne. Each of these three was a double, one head with two faces looking out in opposite directions, four arms and legs, and two sets of genitalia. They moved about on the earth with a great deal more freedom and power than humans do now, for they rolled-ran hand over hand and foot over foot at double speed. In other words, they did cartwheels to get around.
One day, these fast, powerful, but foolish creatures decided to scale Mt. Olympus to attack the gods.
What should the gods do to show the foolish humans the error of their ways? Should they shoot them down with thunderbolts? No, they decided, too boring. They'd done that before to the giants. Besides, who would pour out libations and offer sacrifices to them if they destroyed their worshipers? They had to devise a new punishment.
Zeus thought and thought. Finally he had a brainstorm. Humans were not a real threat, but they did need a dressing down. Their arrogance would be checked if they lost their speed, strength, and confidence. Zeus decided that if they were cut in half, they would be only half as fast and half as strong. Even better, it was a re-usable plan. Should they act up again, he would repeat the operation, leaving them with only one leg and one arm each.
After he revealed his plan to his fellow Olympians, he asked Apollo to join him in putting it into effect. The king of the gods cut the man-man, woman-woman, and man-woman creatures in half and Apollo made the necessary repairs. The face, previously facing out, Apollo turned inward. Then he gathered all the skin together (like a purse) with an opening in the middle as a reminder to mankind of his earlier state.
After the surgery, the half creatures ran around frantically looking for their other halves, seeking them out, embracing them, and trying to join together again. Unable to join, the creatures despaired and began to starve to death in their sorrow. Zeus, again mindful of his need for worship, decided something must be done to recharge the creatures' spirits, so he instructed Apollo to create a means to rejoin temporarily. This Apollo did by turning the genitals to the belly side of the body.
Before, mankind had procreated by dropping seed on the ground. This new system created an interesting new means of producing offspring.
The creatures who had been double women before, naturally sought out women; those who had been androgynous, sought out members of the opposite gender; those who had been double men, sought out the company of men, and not simply for intercourse, but so they could become whole again by being rejoined with their soul mates.