Could you tell me why "survival of the species" is the prime directive and from where that directive came?
It comes as a natural -- indeed, inevitable -- result of the interplay of replication and selection.
Your question is like asking where the "prime directive" of "puddles form when it rains on uneven ground" comes from. There is no separate "form puddles" law of nature -- there doesn't need to be -- it's just an inevitable result of how water droplets migrate in the presence of gravity when falling on the contour of uneven surfaces. Given the mere presence of a) gravity, b) water, and c) uneven ground, puddles (or in extreme cases, lakes or oceans) will inevitably occur, due to the simple interplay of gravity/water/ground. Puddle-formation is not an "extra" ingredient or law, it's a necessary *consequence* of the interplay of simpler entities.
And the same goes for evolution -- it's the inevitable outcome of what happens when variable replication exists in any environment where selection occurs (and selection itself is another inevitable consequent of what happens when replicators interact with their surroundings).
I find your answer unconvincing. It is so just because it is so doesn't answer anything.