Nervous system evolved only once, about 3 billion years after life started, and nothing analogous to it ever evolved in any other lineage. [Urbilaterian]
From Science, July 3 2009, p. 24-26, "On the origin of the nervous system":
Assembling these components into a cell a modern neuroscientist would recognize as a neuron probably happened very early in animal evolution, more than 600 million years ago... Scientists also disagree on which animals were the first to have a centralized nervous system and how many times neurons and nervous sytems evolved independently ... [Leonid Moroz:] "Neurons may have appeared in multiple lineages in a relatively short time."
p. 26:
If the bilaterian ancestor had a diffuse nervous system, centralized nervous systems must have originated multiple times in multiple bilaterian lineages... On the other hand, if the ancestor had a centralized nervous system, several lineages... must have later reverted to a diffuse nervous system. ... Most researchers now agree that equally complex - but anatomically different - brains have evolved in birds, mammals, and other animal lineages, Northcutt says: "At least four or five times independently, ... major radiations of vertebrates have evolved complex brain structure."
We have a sample of one modern human civilization, but there are some hints on how likely it was to happen.
Major types of hints are:
Data for:
Data against:
To me it looks like life, animals with nervous systems, Upper Paleolithic-style Homo, language, and behavioral modernity were all extremely unlikely events (notice how far ago they are - vaguely ~3.5bln, ~600mln, ~3mln, ~200k or ~600k, ~50k years ago) - except perhaps language and behavioral modernity might have been linked with each other, if language was relatively late (Homo sapiens only) and behavioral modernity more gradual (and its apparent suddenness is an artifact). Once we have behavioral modernity, modern civilization seems almost inevitable. Your interpretation might vary of course, but at least now you have a lot of data to argue for your position, in convenient format.