Hints of bacteria on Venus are encouraging, but finding life beyond Earth is the easy part. A new analysis suggests the evolution of human-like intelligence on another planet is more improbable than we like to imagine


30 September 2020

EARTH makes life look easy. Our home planet is teeming with some 9 million species, including at least one smart enough to contemplate intelligent life existing elsewhere in the universe. We love to think it is out there – that we aren’t a one-off, alone in an unimaginably vast cosmos.

A string of discoveries has boosted the idea that extraterrestrial life might be abundant. The growing catalogue of exoplanets, many orbiting within the “habitable zone” of their host stars, points to seemingly ample real estate on which life might be found. Closer to home, subsurface oceans on icy moons in the outer solar system hint that some life-friendly conditions might be commonplace. And then there is last month’s discovery of phosphine in the poisonous atmosphere of Venus, which suggests life might flourish even in seemingly hostile places.

With all that in mind, it is easy to imagine that intelligent life has evolved on at least one planet around one of the 100 billion or so stars in our galaxy. So easy, in fact, that we tend to assume, given the vastness of the visible universe, that there must be other technological civilisations out there. Yet we haven’t heard from them. Why?

In the absence of evidence from deep space, some astronomers have recently returned their focus to Earth – and the only example of intelligent life we have – for a fresh look at the question. What they found meshes with what biologists have been whispering for a while: that anyone expecting to hear from an alien civilisation should settle in for a long wait.

A famous formula

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