According to a Roper poll taken in 2002, two-thirds of the American populace believes that intelligent, extraterrestrial life exists. But that means that one-third is skeptical: A generous slice of the citizenry thinks we might be the cleverest creatures in the Milky Way, or even the entire cosmos.
When I lecture about our hunt for life elsewhere, there are always folks in the audience who share this pessimistic point of view (which surprises me, given that they've voluntarily come to my talk). When I ask what motivates their disbelief, the response usually boils down to this: Extraterrestrial intelligence is too improbable.
Too improbable? Given the recent tide of planet discoveries -- hinting that tens of billions of Earth-size worlds might infest the Milky Way -- you'd think that the case for cosmic company was hardly "improbable."
But there's always the biology card. Sure, habitable worlds might be plentiful, but just because you find a home for ET doesn't mean the lights are on. In Europe, some academics have recently weighed in on the side of the skeptics, claiming to find biological roadblocks that would stall the easy evolution of thinking beings.
Two years ago, Andrew Watson, at the University of East Anglia, made a mathematical model of what he thought were the four transformative steps in the evolution of Homo sapiens: the emergence of bacteria, complex cells, specialized cells (permitting multicellular life), and eventually intelligent creatures with language. This concatenation of biological development is reminiscent of the Drake Equation, and Watson used it for estimating the probability of sentient beings.
What he notes is that we've arrived on the planet almost five billion years after the Sun began to shine. Since our star is no longer a spring chicken, Watson argues that evolution almost missed its opportunity to produce us. That's because the gradual warming of the Sun will soon (within a billion years or so) make Earth too toasty for habitation by sophisticated animals. Ergo, Homo sapiens just made it under the wire, and we're lucky to be here; we won the lottery. Watson figures that the probability of a jackpot is roughly one in ten thousand for any Earth-like world. That's pretty low, and he guesses we'll have a hard time finding ET.
More recently, Nick Lane of University College London and Bill Martin of the University of Dusseldorf have argued that complex life -- including the reader of this blog -- are only in existence because of a "one-off" event billions of years ago, when simple, single-celled organisms swallowed some other bacteria that became their engines of energy -- mitochondria. Lane and Martin argue that without this combination of cellular capabilities, the type of specialized cells that could eventually form complex plants and animals would never have arisen (this is one of the four steps in Watson's chain of development, you'll note). Bottom line? You're the consequence of a biological accident, and an improbable one.
These researchers are not the first to opine that our presence on Earth is unlikely, of course. Evolutionary biologist Stephen Jay Gould made that argument, too. But the question is, are they right?
The answer should be obvious to anyone who's machete'ed their way through a statistics course: We don't know. We have only one example of a world with life. And when you have but a single data point, you don't know whether a phenomenon is commonplace or breathlessly rare.
Frankly, I'm not terribly discouraged by the arguments. Even if Watson is correct, and only 0.01 percent of Earth-like worlds produce intelligence, millions of such species will have arisen in the Milky Way. If so, it's likely that thousands of them are out there right now, enjoying their alien lives. As for the supposed improbability of complex cells, University of Colorado biologist Norman Pace put it to me this way:
My guess is that the origin of life is a common consequence of the origin of planetary systems, and the real question is whether that life survives for a few billion years of evolution. There is nothing special about us so far as I know, and no reason to predict such.
It once again comes down to our inability to make a statistical assessment of just how "lucky" we are. So clearly, we need to search for another example of life.
But the suggestion that we're a very, very special case makes me uneasy. It flies in the face of the so-called Copernican principle and implies that our existence is... well... a miracle.
Apparently one-third of the population likes this idea. But I don't. After all, miracles are science's last resort.
Rabbi Adam Jacobs: A Reasonable Argument for God's Existence
Gregory Cochran: The 10,000 Year Explosion: How Civilization Accelerated Human Evolution
How inevitable is technology? Earth has billions of species, but only humans are technological.
Question: if humans disappear from Earth, will another species ever develop technology? Will chimps evolve radio, travel in space?
These questions cool the ardor of most SETI fans.
The only way for us to say that a specific planet has intelligent life is to be able to communicate with it, which implies that either both we and they have long-range communication technology, or one of us has interstellar travel, or (much less likely) there's intelligent life somewhere in the solar system so we only need interplanetary travel to find them. Humans are only marginally advanced enough to do long-range communications, so it's likely that if we meet any aliens soon they'll have better technology that we do.
And no, humans aren't the only species that do technology. Chimps do technology, I think other apes and monkeys do also, and some birds definitely make tools. On your other question, we'll be lucky if we don't wipe out the other great apes this century, and if humans disappear, it's probably because we've damaged the planet enough that lots of other mammals get wiped out as well.
I mainly bring this up because scifi assumes the universe is full of creatures like us, but there's one such species on earth, so it's an absurd assumption.
A major Biblical scholar believes same: that Adam and Eve were the first Jewish farmers, and the apple represented agriculture, early technology. He even believes he knows where the Garden of Eden is, and he's been right about this stuff before, found several ancient sites.
When you eliminate the impossible, whatever remains--however improbable--must be the truth
Life is here, on Earth. There's no evidence it is anywhere else, and the odds are - at best - incredibly slim that it's on any number of worlds. That's not a miracle, it's a fact.
Most don't understand probability. That's why we have lotteries.
Evolution doesn't assign any goodness or badness or directionality or "progress" to this, it's just that if something sticks around long enough and replicates itself reliably enough you'll have more of it around for longer.
And in the case of evolution, if the stuff happens to change in ways that lead to self-awareness and intelligence, maybe it'll notice that it exists, whereas if it hadn't done that, nobody would have noticed.
Unfortunately for SETI, the volume of the galaxy is just too grand--even when dealing with light and radio. It's sadly plausible that every intelligent species is forever a prisoner of its own system, at least until another revolution or two in physics proves us wrong.
Andrew Watson has drawn his argument even more narrowly than that. He is arguing about Earth-like worlds around very SUN-LIKE STARS.
A main-sequence, G2-type star like our Sun is expected to last 10 billion years, during part of which life can exist here. But a main-sequence G9 star should last a few billion years longer. And after that come K-type stars, which, though they're a bit dimmer and redder than the Sun, should last billions of years longer still.
What's to prevent life from forming in main-sequence, K-type star systems? I don't see any show-stoppers. A K9V star is one tenth as bright as the Sun. A planet about three times closer to a K9V start than Earth is to the Sun would have about the same temperature.
I'll save my thoughts about life on non-Earthlike planets for another post.
There is underwhelming evidence for a notion like that.
http://ecocosmology.blogspot.com/2010/10/shadow-of-time-governs-earth-2.html