Those who don't learn the lessons of an extinct alien civilization's fall may be doomed to repeat it.

Humanity appears to be going down a dangerous path. We've developed weapons powerful enough to off ourselves many times over, for example, and we've been altering Earth's climate for decades without much regard for the serious consequences.

Similar behavior may have led to the demise of advanced alien races around the galaxy, said Avi Loeb, the chair of Harvard's astronomy department. Indeed, this might help explain, at least in part, why we have yet to make contact with ET despite the profusion of habitable real estate in the Milky Way (a puzzle known as the Fermi paradox).

"One possibility is that these civilizations, based on the way we behave, are short-lived," Loeb said last week during a talk at The Humans to Mars Summit in Washington, D.C. "They think short term, and they produce self-inflicted wounds that eventually kill them."

So, the hunt for ET should be wide-ranging enough to spy artifacts left behind by vanished civilizations, he added — evidence such as burned-up planetary surfaces and products of nuclear war swirling in an alien world's air.

Such a find would perhaps be the greatest scientific discovery of all time, and it might have the added benefit of putting our troubled species on a better path.

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