Every theory of life is missing crucial pieces. The standard non-directed model of evolution bounded by random mutations and natural selection is demonstrably insufficient to the task, and raining down even single celled replicating organisms frozen and revived from meteorites (which haven't been found) is still insufficient because the effective novelty production machinery simply isn't there.
The only theory at present which in fact is just based on phenomenology and lacking a meterial theory at this point is Rupert Sheldrakes "Theory of Formative Causation". This doesn't help us at the moment because it involves "fields" which thus far we have no means for detecting. This in and of itself isn't a cause for alarm, but it is cause for annoyance.