"Yes, our law tends to be based on what is described as 'natural law'---those inherent notions that humans have (ex. killing=bad) but were these not imbued by natural selection to allow for continuance of the species?"
The interesting thing is that even an absolute fucking nutbar like Lafayette Ronald Hubbard would have agreed with you, on this one.
It's interesting (well, perhaps more 'irritating' than 'interesting') to note that we, as "sentient" organisms are driven to maldefer our own nature to protect and promulgate the continuation of our genus by the very thing that goD supposedly gave us of his image: free will.
It seems obvious that one can have their cake and eat it, too. Perhaps we could leave a slice cast in bronze.