The Meaning of Human Existence

by Edward O. Wilson

Might other planets of the Solar System harbor such extremophiles, as we Earth biologists call them? On Mars, life could have evolved in the early seas and survive today in deep aquifers of liquid water. Abundant parallels of such subterranean regression exist on Earth. Advanced cave ecosystems abound on all continents. They include at the least microbes, and in most parts of the world insects and spiders and even fish as well, all with anatomy and behavior specialized for life in totally dark, impoverished environments. Even more impressive are the SLIMEs (subterranean lithoautotrophic microbial ecosystems), distributed through soil and rock fissures from near the surface to a depth of up to 1.4 kilometers and comprising bacteria that live on energy drawn from the metabolism of rocks. Feeding on them are a recently discovered new species of deep subterranean nematodes, tiny worms of a general kind abundant everywhere on the surface of the planet.

  There are places in the Solar System in addition to Mars to search for organisms, at least those with the biology of what we call extremophile on Earth. It makes sense to look for microbes in aquatic islets beneath or around the icy geysers of Enceladus, Saturn’s superactive little moon. And as opportunity arises, we should (in my opinion) probe the vast aquatic oceans of Jupiter’s moons Callisto, Europa, and Ganymede, as well as Titan, a larger moon of Saturn. All are encased in thick shells of ice. Brutally cold and lifeless on the surface they may be, but underneath are depths warm enough to hold liquid organisms. We can eventually, if we wish, drill through the shells to reach that water—just as scientific explorers are now doing above Lake Vostok, sealed off by the Antarctic ice cap for a million years or more.

  Someday, perhaps in this century, we, or much more likely our robots, will visit these places in search of life. We must go and we will go, I believe, because the collective human mind shrivels without frontiers. The longing for odysseys and faraway adventure is in our genes.

  The ultimate destiny of the outward-bound astronomers and biologists is of course to reach still farther, very much farther, across almost incomprehensibly far distances into space, to the stars and potentially life-bearing planets around them. Because deep space is transparent to light, the detection of very remote alien life is very much a possible dream. Many potential targets will be found in the mass of data collected by the Kepler space telescope before it partly failed in 2013, together with other space telescopes planned and the most powerful ground-based telescopes. And soon. By mid-2013 almost 900 extrasolar planets had been detected, with thousands more believed likely to be found in the near future. One recent extrapolation (let me pause: extrapolation is admittedly a risky procedure in science) predicts that a fifth of stars are orbited by Earth-sized planets. In fact, the most common class of systems detected thus far include planets one to three times Earth’s size, thus with gravity similar to that of Earth. So, what does that tell us about the potential of life in outer space? First, consider the estimate that ten stars of various kinds exist within ten light-years of the Sun, about 15,000 within 100 light-years, and 260,000 within 250 light-years. Keeping in mind life’s early origin in the geological history of Earth as a clue, it is plausible that the total number of life-bearing planets as close as 100 light-years could be in the tens or hundreds.

  To find even the simplest form of extraterrestrial life would be a quantal leap in human history. In self-image, it would confirm humanity’s place in the Universe as both infinitely humble in structure and infinitely majestic in achievement.

  Scientists will want (desperately) to read the genetic code of the extraterrestrial microbes, providing such organisms can be located elsewhere in the Solar System and their molecular genetics studied. This step is feasible with robotic instruments, eliminating the need of bringing the organisms to Earth. It would reveal which of two opposing conjectures about the code of life is correct. First, if the microbial E.T.s have a code different from that on Earth, their molecular biology would be different to a comparable degree. And if such proves to be the case, an entirely new biology might be instantly created. We would further be forced to conclude that the code used by life on Earth is probably only one of many possible in the galaxy, and that codes in other star systems have originated as adaptations to environments very different from those on Earth. If, on the other hand, the code of extraterrestrials is basically the same as that of native Earth organisms, it could suggest (but not prove, not yet) that life everywhere can only originate with one code, the same as in Earth’s biological genesis.

  Alternatively, perhaps some organisms manage interplanetary travel by drifting through space, living in cryogenic dormancy for thousands or millions of years, protected somehow from galactic cosmic radiation and surges of solar energetic particles. Interplanetary or even interstellar travel by microbes, called pangenesis, sounds like science fiction. I wince a bit just bringing it up. But it should be considered as at least a remote possibility. We know too little about the vast array of bacteria, archaeans, and viruses on Earth to make any call about the extremes of evolutionary adaptation, here and elsewhere in the Solar System. In fact, we now know that some Earth bacteria are poised to be space travelers, even if (perhaps) none has ever succeeded. A large number of living bacteria occur in the middle and upper atmosphere, at altitudes of six to ten kilometers. Composing an average of around 20 percent of the particles with diameters of 0.25 to 1 micron in diameter, they include species able to metabolize carbon compounds of kinds found all around them in the same strata. Whether some are also able to maintain reproducing populations, or on the contrary are just temporary voyagers lifted by air currents away from the land surface, remains to be learned.

  Perhaps the time has come to seine-haul for microbes at varying distances beyond Earth’s atmosphere. The nets could be composed of ultrafine sheets towed by orbiting satellites through billions of cubic kilometers of space, then folded and returned for study. Such a foray conducted out into space might produce surprising results. Even new, anomalous species of Earth-born bacteria able to endure the most hostile conditions—or the absence of such organisms—would make the effort worthwhile. It would help answer two of the key questions of astrobiology: What are the extreme environmental conditions in which current members of Earth’s biosphere can exist? And might organisms originate in other worlds in conditions of comparable severity?

  10

  A Portrait of E.T.

  What I am about to tell you is speculation, but not pure speculation. It is that by examining the myriad animal species on Earth and their geological history, then extending this information to plausible equivalents on other planets, we can make a rough sketch of the appearance and behavior of intelligent extraterrestrial organisms. Please don’t leave me at this point. Refrain from dismissing this approach out of hand. Instead, call it a scientific game, with the rules changing to fit new evidence. The game is well worth playing. The payoff, even if the chance of contact with human-grade aliens or higher proves forever vanishingly small, is the building of a context within which a sharper image of our own species can be drawn.

  Granted there is temptation to leave the subject to Hollywood, to the creation of the nightmarish monsters of Star Wars or the Americans-in-punk-makeup populating Star Trek. Learning about extraterrestrial microbes is one thing: it is not difficult to imagine in broad principles the self-assembly of primitive organisms at the level of Earth’s bacteria, archaeans, picozoans, and viruses; and scientists may soon find evidence of such microbial life on other planets. But it is an entirely different matter to picture the origin of extraterrestrial intelligence at the human grade or higher. This most complex level of evolution has occurred on Earth only once, and then only after more than six hundred million years of evolution within a vast diversity of animal life.

  The final evolutionary steps prior to the human-level singularity, that is, altruistic division of labor at a protected nest site, has occurred on only twenty known occasions in the history of life. Three of the lines that reached this final preliminary level are mammals, namely
two species of African mole rats and Homo sapiens—the latter a strange offshoot of African apes. Fourteen of the twenty high achievers in social organization are insects. Three are coral-dwelling marine shrimp. None of the nonhuman animals has a large enough body, and hence potential brain size, needed to evolve high intelligence.

  That the prehuman line made it all the way to Homo sapiens was the result of our unique opportunity combined with extraordinarily good luck. The odds opposing it were immense. Had any one of the populations directly on the path to the modern species suffered extinction during the past six million years since the human-chimpanzee split—always a dire possibility, since the average geological life span of a mammal species is about five hundred thousand years—another hundred million years might have been required for a second human-level species to appear.

  Because of all of the pieces that likely must also fall in place beyond the Solar System, intelligent E.T.s are also likely to be both improbable and rare. Given that, and assuming they exist at all, it is reasonable to ask how close to Earth might E.T.s at the human grade or higher be found. Allow me an educated guess. Consider first the many thousands of large terrestrial animal species that have flourished on Earth for the past four hundred million years, with none but our own making the ascent. Next, consider that while 20 percent or more star systems may be circled by Earthlike planets, only a small fraction may carry liquid water and also possess a Goldilocks orbit (to remind you, not so close to the mother star to be baked, not so distant to be kept permanently deep-frozen). These pieces of evidence are admittedly very slender, but they give reason to doubt that high intelligence has evolved in any of the 10 star systems within 10 light-years of the Sun. There is a chance, slight but otherwise impossible to judge reliably, that the event has occurred within a distance of 100 light-years of the Sun, a radius encompassing 15,000 star systems. Within 250 light-years (260,000 star systems), the odds are dramatically increased. At this distance, if we work strictly off the experience of Earth, the uncertain and marginally possible changes to the probable.

  Let’s grant the dream of many science fiction writers and astronomers alike that civilized E.T.s are out there, even if at this almost incomprehensible distance. What might they be like? Permit me to make a second educated guess. By combining the evolution and peculiar properties of hereditary human nature with known adaptations by millions of other species in the great biodiversity of Earth, I believe it’s possible to produce a logical albeit very crude hypothetical portrait of human-grade aliens on Earth-like planets.

  E.T.s are fundamentally land-dwellers, not aquatic. During their final ascent in biological evolution to the human grade of intelligence and civilization, they must have used controlled fire or some other easily transportable high-energy source to develop technology beyond the earliest stages.

  E.T.s are relatively large animals. Judging from Earth’s most intelligent terrestrial animals—they are, in descending rank order, Old World monkeys and apes, elephants, pigs, and dogs—E.T.s on planets with the same mass as Earth or close to it evolved from ancestors that weighed between ten and a hundred kilograms. Smaller body size among species means smaller brains on average, along with less memory storage capacity and lower intelligence. Only big animals can carry on board enough neural tissue to be smart.

  E.T.s are biologically audiovisual. Their advanced technology, like our own, allows them to exchange information at various frequencies across a very broad sector of the electromagnetic spectrum. But in ordinary thinking and talking among themselves they use vision just like us, employing a narrow section of the spectrum, along with sound created with waves of air pressure. Both are needed for rapid communication. E.T.s’ unaided vision may allow them to see the world in ultraviolet in the manner of butterflies, or some other, still unnamed primary color outside the range of wave frequency sensed by humans. Their auditory communication may be immediately perceived by us, but it could also easily be at too high a pitch, as used by katydids or many other insects, or too low, as practiced by elephants. In the microbial worlds on which the E.T.s depend, and in probably most of the animal world, most communication is by pheromones, secreted chemicals that convey meaning in their smell and taste. The E.T.s, however, cannot employ this medium any more than we can. While it is theoretically possible to send complex messages by the controlled release of odor, the frequency and amplitude modulation required to create a language is possible across only a few millimeters.

  Finally, might E.T.s read facial expressions or sign language? Of course. Thought waves? Sorry, I don’t see any way that’s possible, except through elaborate neurobiological technology.

  Their head is distinct, big, and located up front. The bodies of all land-dwelling animals on Earth are elongated to some extent, and most are bilaterally symmetrical, with the left and right sides of their bodies reciprocal mirror images. All have brains with key sensory input located in the head, adapted in location for quick scanning, and integration, and action. E.T.s are no different. The head is also large compared to the rest of the body, with a special chamber to accommodate the necessarily huge memory banks.

  They possess light to moderate jaws and teeth. Heavy mandibles and massive grinding teeth on Earth are the marks of dependence on coarse vegetation. Fangs and horns denote either defense against predators, or competition among males of the same species, or both. During their evolutionary ascent, the ancestors of the aliens almost certainly relied on cooperation and strategy rather than brute strength and combat. They were also likely to be omnivorous, as are humans. Only a broad, high-energy meat-and-vegetable diet could produce the relatively large populations needed for the final stage of the ascent—which in humans occurred with the invention of agriculture, villages, and other accoutrements of the Neolithic revolution.

  They have very high social intelligence. All social insects (ants, bees, wasps, termites) and the most intelligent mammals live in groups whose members continuously and simultaneously compete and cooperate with one another. The ability to fit into a complex and fast-moving social network gives a Darwinian advantage both to the groups and to individual members that form them.

  E.T.s have a small number of free locomotory appendages, levered for maximum strength with stiff internal or external skeletons composed of hinged segments (as by human elbows and knees), and with at least one pair of which are terminated by digits with pulpy tips used for sensitive touch and grasping. Since the first lobe-finned fishes invaded the land on Earth about four hundred million years ago, all of their descendants, from frogs and salamanders to birds and mammals, have possessed four limbs. Further, among the most successful and abundant land-dwelling invertebrates are the insects, with six locomotory appendages, and spiders, with eight. A small number of appendages is therefore evidently good. It is moreover the case that only chimpanzees and humans invent artifacts, which vary in nature and design from one culture to the next. They do so because of the versatility of soft fingertips. It is hard to imagine any civilization built with beaks, talons, and scrapers.

  They are moral. Cooperation among group members based on some amount of self-sacrifice is the rule among highly social species on Earth. It has arisen from natural selection at both the individual and group levels, and especially the latter. Would E.T.s have a similar inborn moral propensity? And would they extend it to other forms of life, as we have done (however imperfectly) in biodiversity conservation? If the driving force of their early evolution is similar to our own, a likely possibility, I believe they would possess comparable moral codes based upon instinct.

  It might not have escaped your attention that I’ve thus far tried to envision E.T.s only as they were at the beginning of their civilizations. It is the equivalent of a portrait of humanity drawn during the Neolithic era. Following that period our species worked its way by cultural evolution, across ten millennia, from the rudiments of civilization in scattered villages to the technoscientific global community of today. It is likely by chance alone tha
t extraterrestrial civilizations made the same leap not just millennia ago but thousands of millennia ago. With the same intellectual capacity we already have, and possibly a great deal more, might they have long since engineered their own genetic code in order to change their biology? Did they enlarge their personal memory capacities and develop new emotions while diminishing old ones—thereby adding boundless new creativity to the sciences and the arts?

  I think not. Nor will humans, other than correcting disease-causing mutant genes. I believe it would be unnecessary for our species’ survival to retrofit the human brain and sensory system, and, in one basic sense at least, it would be suicidal. After we have made all of the cultural knowledge available with only a few keystrokes, and after we have built robots that can outthink and outperform us, both of which initiatives are already well under way, what will be left to humanity? There is only one answer: we will choose to retain the uniquely messy, self-contradictory, internally conflicted, endlessly creative human mind that exists today. That is the true Creation, the gift given us before we even recognized it as such or knew its meaning, before movable print and space travel. We will be existential conservatives, choosing not to invent a new kind of mind grafted on top of or supplanting the admittedly weak and erratic dreams of our old mind. And I find it comforting to believe that smart E.T.s, wherever they are, will have reasoned the same way.

  Finally, if E.T.s know of Earth’s existence at all, will they choose to colonize it? In theory, it may have seemed possible and contemplated at any time by many of them over the past millions or hundreds of millions of years. Suppose a conqueror E.T. species has arisen somewhere in our neighborhood of the galaxy since the time of Earth’s Paleozoic Era. Like our species, it was from the beginning driven by an impulse to invade all of the habitable worlds it could reach. Imagine that its drive for cosmic lebensraum began one hundred million years ago, in an already old galaxy. Also, imagine (reasonably) that it took ten millennia from launch to reach the first habitable planet; and from there, with the technology perfected, the colonists devoted another ten millennia to launch an armada sufficient to occupy ten more planets. By continuing this exponential growth, the hegemons would have already colonized most of the galaxy.