The showdown over the U.S. debt ceiling demonstrates a crucial failing of human beings: We are systematically incapable of understanding how precarious our existence, or the continuance of our currently familiar condition, really is.

Think carefully about life on this planet and you’re inevitably led, as Charles Darwin was, to think about adaptation.

An organism’s characteristics reflect the conditions under which its ancestors evolved — conditions that enabled them to survive at least well enough to have viable offspring. The fat of a hippopotamus, the sleek shape of a bird’s wing represent well-tuned solutions to pressing problems.

The story of evolution, however, is actually less about adaptation than it is about the failure to do so. Roughly 99 percent of all the species ever known to exist have gone extinct.

A similar pattern holds for businesses, cities and civilizations: The vast majority goes extinct fairly quickly, while a few standouts persist over much longer periods. Whether you are Tyrannosaurus rex, the Roman Empire or Google Inc., your future is never certain.

Moreover, everything we know about history — in biology, geology, financial markets and other human affairs — points to a pattern in which long periods of relative quiescence are sporadically broken apart by sharp episodes of dramatic, transforming change. This is natural.

All this adds some perspective to the brinkmanship of tea party zealots, bent as they are on flirting with economic disaster by risking a default on U.S. government debt. They seem to believe in a mysterious guarantee that America’s place in the world cannot change: Next year, the dollar will still be the global reserve currency, and the U.S. economy will still be viewed as a haven of stability and safety.

Perhaps the whole debacle will turn out to be of no lasting importance. That said, it’s not government as usual when a major political party threatens to punish the entire U.S. economy unless it gets its way.

Nobody ever said that maintaining a functioning democracy would be easy. Almost 2,500 years ago, the Greek philosopher Plato projected that representative democracy would always be unstable and prone to collapse due to the ability of powerful interests to sway voters to act against the real interests of the state. He worried, as the philosopher Jorn Bramann put it, that citizens would come over time to “live in a cognitive haze that reduces them to voting on the basis of uninformed convictions, catchy slogans, and altogether vague hunches and feelings.”

Think about the tea party, about loaded terms such as “death panels.”

Think about the “grass-roots” movement to defund the Patient Protection and Affordable Care Act, which was carefully orchestrated by a coterie of wealthy interests, often anonymously.

Consider the U.S. congressman who said Republicans have to “get something out of” the battle over government funding, “and I don’t know what that even is.”

Our democracy, it seems, faces the challenge of adapting to changing circumstances.

Technology, especially the Internet and social media, have transformed the way we communicate with one another, altering the potential to influence opinions and behavior. There’s little reason to expect institutions that were previously stable to remain that way.

The idea that we have solved or even can solve the problem of government is a dangerous illusion. Democracy is a great idea that demands constant adjustment.

Bacteria thrive on Earth not because they have finally and perfectly solved the problem of adaptation, but because they are so adaptable. They solve the problem of survival over and over.

Perhaps, as a result of our impressive history of government stability, mired only here and there in major dysfunction, we’ve come to forget the truly fragile nature of stable, functioning government.

The tea partiers may be having fun, but they should be careful not to underestimate the consequences of their actions.

Mark Buchanan, a theoretical physicist and the author of “Forecast: What Physics, Meteorology and the Natural Sciences Can Teach Us About Economics,” is a Bloomberg View columnist. E-mail: buchanan.mark@gmail.com.

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