Regarding the paper I linked to in my last post, I just want briefly to emphasize an implicit conclusion from it that may not have been obvious. If you remember, the difference in architecture of E. coli compared to the Linux operating system was taken by the authors as evidence of the difference in “the design principles of the two systems” (sic). Human developers aim at cost-effectiveness and top-down design, whereas bacteria take a bottom-up approach suited to random mutation and natural selection:
The process of biological evolution via random mutation and subsequent selection tightly constrains the evolution of regulatory network hubs. The [Linux] call graph, however, exhibits rapid evolution of its highly connected generic components, made possible by designers continual fine-tuning. These findings stem from the design principles of the two systems: robustness for biological systems and cost effectiveness (reuse) for software systems.
But, as I pointed out in the previous post, the paper goes on to say near the end of its discussion section:
Previous studies have made the related finding that as one moves towards more complex organisms, the transcriptional regulatory network has an increasingly top-heavy structure with a relatively narrow base. Thus, it may be that further analysis will demonstrate the increasing resemblance of more complex eukaryotic regulatory networks to the structure of the Linux call graph
Advanced organisms, then, do not share the “tight constraints” imposed by mutation and natural selection. This would imply, if the basic thesis of the paper is correct, that the mechanisms of evolution in these organisms are something other than random mutation and natural selection.