The 'higher authority' is your Soul - the REAL YOU. Not the human you in a state of amnesia.
FREE WILL. It is ONLY the Soul that has choice as to when it incarnates. We may get input, but it is our choice.
However, just as when going from your house to another's, a door must be opened. We cannot just blast through to this dimension at any moment. It first cooperates with the Universal order of things, which Superstring Theory is starting to put into scientific terms. It also cooperates with biology, but biology does not define it. It is the manifestation of it.
Ah now I follow, yes I do believe the soul has a choice, (to a point, we are sent to make that choice) not only that it's choice is directed towards the lessons that need to be learned, the karma that needs to be fulflled. Once the choice has been made, and the soul enters all is wiped clean of the memory or reason for that choice, so that the lessons are not influenced and are in fact learned. This is an extremely painful stand, because we find ourselves on a plain with things like child abuse, born into poverty, illness. There are many who believe we choose our parents, and do so with reason. The whole foundation on incarnation as far as I'm concerned is based on that "what we must finish before we can move on." Some are lucky and may fulfill this in heaven, others will have to return and do it via the flesh.