Jared Diamond - The rise and fall of the third chimpanzee

While humans are unique among Earth's species, the enormous number of stars suggests that intelligent creatures like us must have evolved elsewhere in the universe. If so, why have we not been visited by their flying saucers? The insights that woodpeckers provide into the supposed inevitability of convergent evolution help us reassess the possibility that we are unique in the accessible universe as well as on Earth.

The next time you are outdoors on a clear night away from city lights, look up at the sky and get a sense of the myriads of stars. Next, find a pair of binoculars, train them on the Milky Way, and appreciate how many more stars escaped your naked eye. Then look at a photo of the Andromeda Nebula as seen through a powerful telescope to realize how enormous is the number of stars that escaped your binoculars as well.

Once all those numbers have sunk in, you will finally be ready to ask how humans could possibly be unique in the universe. How many civilizations of intelligent beings like ourselves must be out there, looking back at us? How long before we are in communication with them, before we visit them, or before we are visited?

On Earth, we certainly are unique. No other species possesses language, art, or agriculture of a complexity remotely approaching ours. No other species abuses drugs. But we have seen in the last four chapters that, for each of those human hallmarks, there are many animal precedents or even precursors. Accept for the moment the assumption that the universe contains innumerable other planets on which life evolved. Do not those considerations suggest that some other species on some other planets have also extended such widespread precursors as far as the level of our own intelligence, technical ability, and communication skills? While no other species on Earth is now wondering where else in the universe there exists intelligent life, such species must exist elsewhere. Alas, most human hallmarks lack effects detectable at a distance of many light-years. If there were creatures enjoying art or addicted to drugs on planets orbiting even the nearest stars, we would never know it. But fortunately there are two signs of intelligent beings elsewhere that might be detectable on Earth—space probes and radio signals. We ourselves are already becoming effective at sending out both, so surely other intelligent creatures have mastered the necessary skills. Where, then, are the expected flying saucers? This seems to me one of the greatest puzzles in all of science. Given the billions of stars, and given the abilities that we know did develop in our own species, we ought to be detecting flying saucers or at least radio signals. There is no question about there being billions of stars. What is there about the human species, then, that could explain the missing saucers? Could we really be unique not only on Earth, but also in the accessible universe? In this chapter I shall argue that we can obtain a fresh perspective on our uniqueness by looking carefully at some other well-known creatures here on Earth—woodpeckers!

For a long time, people have asked themselves such questions. Already around 400 BC the philosopher Metrodorus wrote, 'To consider the Earth the only populated world in an infinite space is as absurd as to assert that in an entire field sown with millet, only one grain will grow. Not until 1960, however, did scientists make a serious first attempt to find the answer, by listening (unsuccessfully) for radio transmissions from two nearby stars. In 1974 astronomers at the giant Arecibo radio telescope tried to establish an interstellar dialogue, by beaming a powerful radio signal to the star cluster M13 in the constellation Hercules. The signal described to Hercules' denizens what we earthlings look like, how many of us there are, and where the Earth is located in our solar system. Two years later the search for extraterrestrial life provided the main motivation behind the Viking missions to Mars, whose cost of about a billion dollars dwarfed all the US National Science Foundation's expenditures (since its inception) for classifying the life known to exist on Earth. More recently the US government has decided to spend a further hundred million dollars to detect radio signals from any intelligent beings who might exist outside our solar system. Several spacecraft that we launched are now heading out of our solar system, carrying sound tapes and photographic records of our civilization to inform spacelings who might be encountered.

It is easy to understand why lay people as well as biologists would consider the detection of extraterrestrial life as possibly the most exciting scientific discovery ever made. Just imagine how it would affect our self-image to find that the universe holds other intelligent creatures, with complex societies, languages, and learned cultural traditions, and capable of communicating with us. Among those of us who believe in an afterlife and an ethically concerned deity, most would agree that an afterlife awaits humans but not beetles (or even chimpanzees). Creationists believe that our species had a separate origin through divine creation. Suppose, though, that we should detect on another planet a society of seven-legged creatures more intelligent and ethical than we are, and able to converse with us, but having a radio receiver and transmitter in place of eyes and a mouth. Shall we believe that those creatures (but still not chimps) share the afterlife with us, and that they too were divinely created? Many scientists have tried to calculate the odds of there being intelligent creatures out there, somewhere. Those calculations have spawned a whole new field of science termed exobiology—the sole scientific field whose subject matter has not yet been shown to exist. Let's now consider the numbers that encourage exobiologists to believe in their subject matter. Exobiologists calculate the number of advanced technical civilizations in the universe by an equation known as the Green Bank formula, which multiplies a string of estimated numbers. Some of those numbers can be estimated with considerable confidence. There are billions of galaxies, each with billions of stars. Astronomers conclude that many stars probably have one or more planets each, and that many of those planets probably have an environment suitable for life. Biologists conclude that, where conditions suitable for life exist, life will probably evolve eventually. Multiplying all of those probabilities or numbers together, we conclude that there are likely to be billions of billions of planets supporting living creatures. Now let's estimate what fraction of those planetary biotas include intelligent beings with an advanced technical civilization, which we will define operationally as a civilization capable of interstellar radio communication. (This is a less demanding definition than flying saucer capability, since our own development suggests that interstellar radio communication will precede interstellar probes.) Two arguments suggest that that fraction may be considerable. Firstly, the sole planet where we are certain that life evolved—our own—did evolve an advanced technical civilization. We have already launched interplanetary probes. We have made progress with techniques for freezing and thawing life apd for making life from DNA—techniques relevant to preserving life as we know it for the long duration of an interstellar trip. Technical progress in recent decades has been so rapid that manned interstellar probes surely will be feasible within a few centuries at the very most, since some of our unmanned interplanetary probes are already on their way out of our solar system. However, this first argument suggesting that many planetary biotas have evolved advanced technical civilizations is not a compelling one. To use the language of statisticians, it suffers from the obvious flaw of very small sample size (how can you generalize from one case?) and very high ascertainment bias (we picked out that one case precisely because it evolved our own advanced technical civilization).