In my previous blog post, I talked about the likelihood – or unlikelihood – of your existence. The fact that you’re here, and I’m here, is contingent on a vast array of happenings that all had to come about first.
To narrow things down a bit, let’s say that the first few hurdles have already been met: Suppose we already have a universe with the sorts of physical parameters and physical laws that we now observe. And let’s say that universe is filled with an enormous number of stars with an enormous number of planets. Given all of that, what are the odds that you’d end up with (a) living things and (b) intelligence?
Over the last decade or so, astronomers have found more than 500 planets orbiting stars beyond our own sun. Recently, the first “potentially habitable” planet was announced, based on data from the orbiting Kepler telescope. NASA already sponsors research on “astrobiology” – roughly, the science of figuring out what kind of life might be “out there.” And most scientists, I suspect, wouldn’t be shocked if some sort of definitive sign of extraterrestrial life were discovered within the next couple of decades. Thrilled, but not shocked. We don’t have any numbers yet, of course, but it’s worth noting that simple one-celled creatures sprung up on our planet within 1.7 billion years or so of its formation (which doesn’t mean life sprang up overnight; but still, that’s sort of fast in terms of the planet’s 4.5-billion-year history).
But intelligent life is another matter. On our planet, intelligence is the new kid on the block. Our own species, Homo sapiens, have been around for about 200,000 years – a mere speck in terms of Earth’s history. And we’ve only been using the tools of science for about 400 years.
Now, it’s hard to draw conclusions based on one data point, but we can always engage in a bit of educated speculation. This is where things get messy, but, they get messy in an interesting way. A good starting point is the late 20th-century debate between two great evolutionary biologists, Stephen J. Gould and Simon Conway Morris.
Stephen Jay Gould argued, in a nutshell, that the appearance of human beings was highly contingent, that is, it was dependent on a whole series of earlier evolutionary happenings, and therefore very “unlikely.” As Gould explained in his book, Wonderful Life: Life as we know it would have been profoundly different if conditions at the start of the evolutionary process, and along the way, had been only slightly different. The very features that make human beings human – intelligence and language in particular – are radically contingent. In Gould’s words: “Replay the tape a million times from the beginning, and I doubt that anything like Homo sapiens would ever evolve again.”
Note, Gould fought tirelessly against the Creationist movement, but religious opponents of Darwinism, whether creationists or proponents of “intelligent design,” just loved hearing about how unlikely it was for humans to appear on this planet: after all, they argued, what better proof that a loving God had engineered it all.
At any rate, Gould’s view wasn’t the only game in town, even among evolutionists. Simon Conway Morris takes quite a different view, hinted at in the title of his book, Life’s Solution – Inevitable Humans in a Lonely Universe. Replay the tape, he says, and the same broad patterns will emerge. The reason is something called “convergence”: roughly, if similar environments appear, then similar adaptations will appear also. For example, the eye has evolved as many as 40 times, in various lineages, over millions of years.
On the other hand, the very things that seem to make humans human – such as the use of complex symbolic language – appear to have arisen only once. Moreover, full-blown language seems to have appeared only after Homo sapiens had already lived on this planet for tens of thousands of years. In other words, while language may have arisen as an adaptation, it isn’t just a matter of biology. As Ian Tattersall of the American Museum of Natural History puts it: “Human symbolic consciousness, which is the underpinning of our cognitive singularity, is a very recent acquisition in the human lineage. And, even more importantly, it’s not a simple extrapolation of the trends that preceded it.”
Which means that even if life itself is common in the universe, linguistic, symbol-using creatures like ourselves may be quite rare indeed. This may be the reason that all of our SETI efforts – the search for extraterrestrial intelligence, primarily via searches for radio signal – have turned up nothing, after a half-century of scanning the heavens.
In Part One of this blog post, I mentioned one of the works of literature that re-kindled my interest in this subject – Italo Calvino’s Cosmicomics. I focused in particular on the short story “How Much Shall We Bet,” in which two characters make an endless series of bets regarding what sorts of things will happen in their universe. They’d don’t specifically bet on the appearance of intelligent life, but they may as well have; it underlies all the other developments that come after.
In Calvino’s story, the character named Dean is the skeptic; he always bets no. And in this case, I’d have to side with him. Worlds may be likely, oceans and continents may be likely, even life may be likely. But the stuff that makes us human – from ploughs to pyramids, from fettucini to Facebook – may be unique to our world, the slings and arrows of outrageous fortune, never to be repeated.
The Weak Link in the Chain: Intelligence by PLOS Blogs Network, unless otherwise expressly stated, is licensed under a Creative Commons Attribution 4.0 International License.