In cruising across the Internet, perusing information about unrest in Iran, potential currency collapse and other assorted miseries, an advertizement popped up somewhere along the way about a book that promises to help readers survive the collapse of civilization.

Not merely survive degradation of the neighborhood or hardship associated with economic recession, mind you, but the end of civilization as we know it. Back to an era of stone axes and cave clans.

The ad conjures up various sources of this cataclysm, like a terrorist attack on the power grid using an electromagnetic pulse device, or perhaps the rise of a drug-resistant superbug that kills millions.

To this doomsday list one might add running afoul of wayward comets or other space rocks, or encountering a mutant form of athlete's foot from the Amazon Basin that devours legs up past the knees. The dark shadows of imagination have no limits.

The book offers a number of survival tips. Among these is keeping a well-stocked propane barbecue for emergency cooking, although it's hard to see how this would be sufficient to keep the Four Horsemen of the Apocalypse from dropping by for dinner if that were their intent.

Neither, I suspect, would stockpiling money or planning emergency escape routes provide more than brief respite. If the world descends into Thunderdome, neither barbecue grills nor greenback dollars are likely to account for much.

Doomsday scenarios have been around for ages, and sometimes there is good cause to fear the End of Time has arrived, as when the Black Death of the 14th century killed perhaps half the people of Europe.

But Europe clawed its way past the plague. Indeed, some scholars argue that the Black Death, horrific as it was, sowed the seeds of the Renaissance.

It's reasonable to take measures forestalling calamity. But of what use is imagining the worst as if it had already happened, that a virus looms as the new Great Plague while even greater harm is done by pestilences largely ignored? The swine flu has accounted for fewer than 50 victims in the U.S.; every year, tobacco claims more than 400,000.

We can develop vaccines against viruses and pass laws to help inoculate ourselves against a recurrence of reckless collective behavior, in the banking sector and otherwise.

Maybe the world economy will disintegrate. But it hasn't yet. Maybe the sun won't come up tomorrow, but why live already in a darkness that does not end by obsessing about such things?

What is gained by cowering before hobgoblins of the mind?