Where does theatre really begin? If you asked Aristotle, he would have said, look at your children. It originates in the make-up, or wiring, of human beings themselves. It's one of the things that makes us human. In the third chapter of his great critical treatise, his Poetics, he writes:
Imitation is natural to man from childhood, one of his advantages over the lower animals being this, that he is the most imitative creature in the world, and learns at first by imitation. And it is also natural for all to delight in works of imitation.
-John Sutherland, A Little History of Literature