It has been an exciting month in the world of exobiology, the scientific study of possible life on other planets. A few weeks ago, scientists at Harvard University presented findings indicating that as much as 35 percent of all known planets larger than Earth may be water-rich. Following closely in their wake, researchers at the University of Chicago came out with a study last week in The Astrophysical Journal showing that the amount of water needed for life to develop comes in a much broader range than previously thought. The news has stirred up a lot of hype lately, and many are wondering if we have now reached a point at which it is no longer scientifically acceptable to think that humans are alone in the cosmos.
The answer, scientists in the relevant areas of expertise say, is yes and no. Yes—there are most likely other forms of life in the cosmos. No—there are probably not other intelligent life forms.
That life is likely to have evolved elsewhere in the universe is pretty uncontroversial among biologists. After all, not only are there billions of other planets in our galaxy, a good number of which appear to possess the conditions for life; there are billions of other galaxies in the observable universe. In fact, with the impressive advances in exobiology over the last thirty years or so, we might even be sanguine about finding some kind of life in our own solar system.
That intelligent life is likely to have evolved, however, is a different story. Almost no biologists of the relevant type make such a claim, and many of the leading evolutionary biologists of modern times—such towering figures as Ernst Mayr, Theodosius Dobzhansky, George Gaylord Simpson, Stephen Jay Gould, and Francisco J. Ayala—regard(ed) it as astronomically improbable.
“I do not know any serious evolutionist who believes there is intelligent life in the universe,” says Ayala. “The reason why so many physicists believe in that is because they don’t understand evolution. One who understands evolution realizes that no matter how many billions of trillions of trillions of trillions of planets, the probability that intelligent life would have come about is so insignificant that it could never come about again.” Dobzhansky was of a similar mind: “our species, mankind, is almost certainly alone in the universe.” There is “an incredibly low probability for the origin of extraterrestrial intelligence,” Mayr affirmed; “that is why only a few super optimistic biologists are willing to support the SETI [Search for Extraterrestrial Intelligence] project.” And Simpson was emphatic that “it is extremely improbable that [extraterrestrial] forms of life include humanoids.” Even the late Stephen Hawking, a physicist by training, maintained that “we might expect to find many other forms of life in the galaxy, but we are unlikely to find intelligent life,” simply due to biological realities.
Mayr, Dobzhansky, Simpson, and Ayala attribute(d) the widespread belief in extraterrestrial intelligences to the popular misconception, even among many astronomers and physicists, that since intelligence is such an advantageous evolutionary adaptation, evolution will, given enough time and suitable places, inevitably progress toward creatures like us.
The idea is seriously misguided, however. To start with, mankind is not the pinnacle of evolutionary progress any more than the housefly or apple tree—each is the ultimate end of an evolutionary twig. (We are not even the most genetically complex species—that distinction goes to a lesser-known crustacean.) More importantly, however, the number of possible evolutionary pathways leading to intelligence simply pales into utter insignificance beside the number of possible evolutionary pathways that end up with some other successful adaptation.
Intelligence, first of all, is not really any more advantageous evolutionarily than countless other adaptations various species have, or could have, evolved. Think about it: among the trillions of non-intelligent species that have ever inhabited Earth (including, importantly, microbes), many have adapted to their environment and reproduced just as, if not much more, successfully than humans have. As notable evolutionary psychologist Steven Pinker put it, “evolution is about ends, not means; becoming smart is just one option.” Secondly, evolution is driven by totally random mutations, so its direction is unplanned, accidental, and haphazard; it would not progress deterministically toward intelligence, even if intelligence were highly advantageous evolutionarily. Thirdly, since evolution operates by making minor changes on the preceding genome, what evolutionary adaptations can develop are determined completely by the contents of that preceding genome, which, in turn, were determined by the random mutations in the genome before that, and so on down the line. Each of these genomes, moreover, is a product of the environment it happened to find itself in at the time; only genes that allowed the organism to survive there could be passed on. So in order for any one particular complex trait like intelligence to develop, each ancestor must have had just the right genome for subsequent mutations to build on and just the right random mutations to arise, and must have resided in just the right environment at that time for those mutations to be advantageous. The historical causal chain, which on this planet stretched over billions of years, is so incredibly contingent that the probability of it occurring again is virtually zero.
Intelligence is “a glorious evolutionary accident,” as Gould famously declared. Instead of hoping against hope to find it somewhere else, maybe we should use it for a moment to reflect on just how lucky we are to have it.