There's been a recent spurt of linking to this news article in New Scientist about how humans "switch off" during rote tasks. The research in question is Goldberg et al. (Neuron 2006 50: 329-339) and is about those blank periods without self-awareness we humans all have, during which we can find we have driven a car all the way to work or ploughed a field or read an overhyped paper. However, it's the news article that (hopefully mis)quotes the first author and gets my goat:

The brain’s ability to "switch off" the self may have evolved as a protective mechanism, he suggests. "If there is a sudden danger, such as the appearance of a snake, it is not helpful to stand around wondering how one feels about the situation," Goldberg points out.

Er, I doubt it. There's no need to explain how the brain came to be able to "switch off" - the hard part is explaining how it was ever switched on. What evolved was not the ability to shut down introspection during danger but rather the ability to introspect from time to time at all. It's misleading to call lapsing to the default state switching off. Thinking is akin to anaerobic muscle exertion - we can only sustain it for short periods but the hard work can be worth it. Was it James Burke who first pointed out that there is no need to explain why plants do not roam about like us animals but instead seem to sleep though life? He pointed out that it's the animals who need to be explained - why bother to be awake when there's a living to be made being asleep, as amply demonstrated by the entire plant kingdom?

In a feat of self-awareness (and pretensiousness?), I can now quote myself from elsewhere hereabouts

I believe we fool ourselves into thinking we have a continuous experience of existence when really we are blank or mindless for quite worrying amounts of time. I believe this is true of everyone, though I have observed that the force is particularly strong in one or two of my acquaintances.

The puzzles of inattention, sleepwalking, hypnotism, sleep itself, consciousness itself - these are in some ways like quantum mechanics. Not that they're based on quantum phenomena (jeez, no, shut it, Penrose!): instead they're merely(?) deeply counterintuitive and so we have been unable to make as much progress on them as we would like. We just don't have the terminology i.e. the reusable metaphors for the underlying concepts yet. They are profoundly alien to our understanding, and that's a sweet irony and a provocation.