String theory predicts 10 (or 11, or 12) spacetime dimensions, but our Universe has only 4. (Why 4 spacetime dimensions? Stable bound gravitational orbits around spherical masses exist only in 4 spacetime dimensions.)
String theorists postulate postulate that the hidden dimensions are curled up into a Calabi-Yau complex manifold. The topology of the Calabi-Yau manifold determines the DNA of the universe. What is the point of having DNA if you don't use it?
Suppose that there exist laws of physics that allow a universe to reproduce.
Reproducing universes fill the Multiverse with their progeny.
Finding oneself in a reproducting universe would be common.