"Another point. What if protiens, self-replication, the start of life really was a once in the universe or galaxy improbability as many notable biologists (not astronomers) have argued? Or what if the transition to multi-cellular life (it took billions of years here) is also another highly improbable occurance even on a galaxy wide scale? We have no real objective evidence as yet to guide us here."

We know life began early on Earth- this argues against life being improbable event- why did life start in first billion year rather than at a later date if it was mattter of chance? The other thing we know is there has been mass extinction events- impactors and/or other events such as supervolcanos- therefore it's unlikely that multicellular takes a long time, but rather it simply couldn't survive in such an "relatively" unstable time [though it could argued that we [and multicellular life in general are product of the continuous distruption [both on the macro level and smaller regional scale- and this in itself would argue for rarity of more advanced life]. Though of course, in order for animal life to exist we needed the time that it took for plants to create the oxygen that animals use for it's energy needs.