The way emergent properties work is through a process of what in biology is called natural selection, or what Schopenhauer (I <3 Schopenhauer) called Will. Every action, whether human or not, arises from a list of pre-existing possible actions. Actions which have advantages over others are those that happen, in the same way that organisms with advantages brought by mutations tend to be more successful at reproduction. Existence, on a larger scale, is the result of a model much like evolutionary biology.
A totally objective universe without subjective beings in it is incapable of apprehending its own being, and therefore less fit for information transfer (which would be necessary unless you wanted a lifeless, motionless universe) than a universe with subjective beings in it. So out of all possible universes jockeying to be the existant universe, universal states capable of making the universe aware of itself (since we are a part of a larger whole) will tend to arise over those that don't. This is what Jung thought was the relationship between humans and God: a collaborative project.
This particular universe exists out of all other possible universes because observers give it an advantage over other potential universal states.