In this theory, our universe emerged from a black hole in a previous universe; moreover, each black hole in our universe (and other universes) generates yet another universe. Universes that produce lots of black holes therefore have more “progeny” than universes that don’t. The laws of physics are reshuffled slightly with each black hole, and increasingly the multiverse is dominated by universes whose laws are “fine-tuned” to produce black holes.
So what? Well, black holes are formed when massive stars collapse. Stars are massive if they contain heavy elements–elements such as carbon. The selection process thus gives rise to universes such as our own, where carbon and other heavy elements are available as the building material for life.