The cells and fibers of the brain must carry some kind of individual identification tags, presumably cytochemical in nature, by which they are distinguished one from another almost, in many regions, to the level of the single neurons.
In its evolution from a more primitive nervous system, the brain, as an organ with ten or more billion neurons and many more connections between them must have changed and grown as a result of many accidents.stanislaw ulam
As usual, I'm overstating the case to knock a few neurons loose, but the truth is usually somewhere in the muddle, uh, middle.larry wall
Since the universe must contain millions of appropriate planets, consciousness in some form - but not with the paired eyes and limbs, and the brain built of neurons in the only example we know - may evolve frequently. But if only one origin of life in a million ever leads to consciousness, then Martian bacteria most emphatically do not imply Little Green Men.)stephen jay gould