Almost 20 years ago, in the pages of an obscure publication called Bioastronomy News, two giants in the world of science argued over whether SETI — the Search for Extraterrestrial Intelligence — had a chance of succeeding. Carl Sagan, as eloquent as ever, gave his standard answer. With billions of stars in our galaxy, there must be other civilizations capable of transmitting electromagnetic waves. By scouring the sky with radio telescopes, we just might intercept a signal.
But Sagan’s opponent, the great evolutionary biologist Ernst Mayr, thought the chances were close to zero. Against Sagan’s stellar billions, he posed his own astronomical numbers: Of the billions of species that have lived and died since life began, only one — Homo sapiens — had developed a science, a technology, and the curiosity to explore the stars. And that took about 3.5 billion years of evolution. High intelligence, Mayr concluded, must be extremely rare, here or anywhere. Earth’s most abundant life form is unicellular slime.
Since the debate with Sagan, more than 1,700 planets have been discovered beyond the solar system — 700 just this year. Astronomers recently estimated that one of every five sunlike stars in the Milky Way might be orbited by a world capable of supporting some kind of life.
That is about 40 billion potential habitats. But Mayr, who died in 2005 at the age of 100, probably wouldn’t have been impressed. By his reckoning, the odds would still be very low for anything much beyond slime worlds. No evidence has yet emerged to prove him wrong.
Maybe we’re just not looking hard enough. Since SETI began in the early 1960s, it has struggled for the money it takes to monitor even a fraction of the sky. In an online essay for The Conversation last week, Seth Shostak, the senior astronomer at the SETI Institute, lamented how little has been allocated for the quest — just a fraction of NASA’s budget.
“If you don’t ante up,” he wrote, “you will never win the jackpot. And that is a question of will.”
Three years ago, SETI’s Allen Telescope Array in Northern California ran out of money and was closed for a while. Earlier this month, it was threatened by wildfire — another reminder of the precariousness of the search.
It has been more than 3.5 billion years since the first simple cells arose, and it took another billion years or so for some of them to evolve and join symbiotically into primitive multicellular organisms. These biochemical hives, through random mutations and the blind explorations of evolution, eventually led to creatures with the ability to remember, to anticipate and — at least in the case of humans — to wonder what it is all about.
Every step was a matter of happenstance, like the arbitrary combination of numbers — 3, 12, 31, 34, 51 and 24 — that qualified a Powerball winner for a $90 million prize this month. Some unknowing soul happened to enter a convenience store in Rifle, Colo., and — maybe with change from buying gasoline or a microwaved burrito — purchase a ticket just as the machine was about to spit out those particular numbers.
According to the Powerball website, the chance of winning the grand prize is about one in 175 million. The emergence of humanlike intelligence, as Mayr saw it, was about as likely as if a Powerball winner kept buying tickets and — round after round — hit a bigger jackpot each time. One unlikelihood is piled on another, yielding a vanishingly rare event.
In one of my favorite books, “Wonderful Life,” Stephen Jay Gould celebrated what he saw as the unlikelihood of our existence. Going further than Mayr, he ventured that if a slithering creature called Pikaia gracilens had not survived the Cambrian extinction, about half a billion years ago, the entire phylum called Chordata, which includes us vertebrates, might never have existed.
Gould took his title from the Frank Capra movie in which George Bailey gets to see what the world might have been like without him — idyllic Bedford Falls is replaced by a bleak, Dickensian Pottersville.
For Gould, the fact that any of our ancestral species might easily have been nipped in the bud should fill us “with a new kind of amazement” and “a frisson for the improbability of the event” — a fellow agnostic’s version of an epiphany.
“We came this close (put your thumb about a millimeter away from your index finger), thousands and thousands of times, to erasure by the veering of history down another sensible channel,” he wrote. “Replay the tape a million times,” he proposed, “and I doubt that anything like Homo sapiens would ever evolve again. It is, indeed, a wonderful life.”
Other biologists have disputed Gould’s conclusion. In the course of evolution, eyes and multicellularity arose independently a number of times. So why not vertebrae, spinal cords and brains? The more bags of tricks an organism has at its disposal, the greater its survival power may be. A biological arms race ensues, with complexity ratcheted ever higher.
But those occasions are rare. Most organisms, as Daniel Dennett put it in “Darwin’s Dangerous Idea,” seem to have “hit upon a relatively simple solution to life’s problems at the outset and, having nailed it a billion years ago, have had nothing much to do in the way of design work ever since.” Our appreciation of complexity, he wrote, “may well be just an aesthetic preference.”
In “Five Billion Years of Solitude,” by Lee Billings, published last year, the author visited Frank Drake, one of the SETI pioneers.
“Right now, there could well be messages from the stars flying right through this room,” Dr. Drake told him. “Through you and me. And if we had the right receiver set up properly, we could detect them. I still get chills thinking about it.”
He knew the odds of tuning in — at just the right frequency at the right place and time — were slim. But that just meant we needed to expand the search.
“We’ve been playing the lottery only using a few tickets,” he said.