Man was bored and lonely, so he asked his creator for a companion. Creator said sure, I'll give you a most supportive mate, who will stand by your side through thick and thin. Will never question you, nor ever betray you. And above all else, she will be your best friend too - However it's going to cost you an arm and a leg. Man decided to bargain, and said, what can you give me for just a rib? And so the rest is history, with no more mystery.