Where are the extraterrestrials, indeed? The answer will not be found by further belaboring of the sciences; not in astronomy, nor in planetary studies, nor yet in biology. In all honesty, one must acknowledge that at this point there no longer is firm understanding to guide us; we have come down a path that ends in mystery.

Yet it could hardly be otherwise. The search for our galactic neighbors may tantalize future generations; it may serve as the wellspring of much science and art in the space communities of our descendants. If so, then it could hardly admit to a simple and clear resolution at so early a date as the late 1970s.

Still, if we cannot know, at least we may speculate, and speculate we will. What we are now led to pursue is the anthropology of extrasolar cultures. This is a science whose very subject matter is not known to exist. Its pursuit is reminiscent of that of Thales and Democritus, who speculated on the nature of atoms and matter in days when the Parthenon was newly minted. Still, there is no alternative. There are only so many reasonable means of resolving the Fermi paradox:

• Extraterrestrial civilizations do not exist. Yet the last chapter has given good reason why they may have arisen in up to 880,000 locales, then spread across the Galaxy. Or,
• Such civilizations perish by their own hand before they succeed in gaining a galactic foothold. This explanation deserves attention because it would mean there is an interstellar hang-up: that intelligence does not promote long species life. Or,
• Such civilizations exist, but for reasons of their own have not and will not make their presence known to us.

This chapter thus will consider the second and third explanations.

Is there perhaps an interstellar hang-up? This idea, that civilization may bring its own destruction, is not new but is merely a variant on a theme in philosophy over two centuries old. It was Jean Jacques Rousseau who introduced this theme in 1749 with his essay in the Mercure de France on the subject, “Has the progress of science and the arts contributed to the corruption or purification of morals?” In that essay, as well as in such influential books as Emile and The Social Contract, Rousseau argued that prior to the advent of civilization, people had been happy and virtuous, but that modern times had sown corruption and misery and had brought the exploitation of the many by the few. He then went on to argue that by means of appropriate reforms, mankind could be returned to what would be more nearly like his original state of natural goodness.

Rousseau’s work was founded on a fallacy. In his day there was no science of early or primitive man, no way of knowing his beau ideal never existed. His Noble Savage never was found. Yet his influence has been comparable to that of Christ or Mohammed. With elaborations, his doctrines were taken over by Marx and then Lenin. In our own day they echo in such notions as the perfectibility of man and in the urging that we renounce technology and return to the land. They also echo in the exalting of emotion over reason and in the idea that civilizations sow the seeds of their own destruction.

Among the most significant insights that were denied to Rousseau was Darwin’s theory of evolution by natural selection. In any animal population, including man, individuals are neither created equal nor endowed with identical traits. They differ, each from the other; there is variation among them. The variation involves physical traits such as size, speed, ability to withstand hunger, etc., but it also involves behavioral traits. Some animals are more aggressive in the chase, more sensitive in ability to detect prey, more assertive in the scramblings for food or females.

This variation ensures that some will best be fitted to survive and to pass on their genes, while others, less fortunate, will fall to illness or to the predator. However, conditions do not stay the same, and traits that may make species fit in one century may prove much less favorable if the situation in which they live should change.

When conditions change, the variation within a species may endow certain of its members or groups with traits that by chance are better suited to the Jew conditions. It will then be those that are favored and which will be the most fit. In this way, the existence of variation allows species to evolve.

The same is true of cultures. Even nuclear war need not prove a destroyer of intelligent species, for by the cultural adaptation of building shelters and preparing against the threat, many would survive. A nuclear war might well resemble a severe forest fire. In such a fire, there are always some trees with thick bark that survive, as well as brush and seeds that escape destruction. Soon after the fire, the burned-over area begins to show signs of life. As the decades progress, there is a forest succession, as one by one the old species return. Within a century or less, the succession has reached maturity, and the new forest is virtually indistinguishable from what had existed before the fire. The life of a forest can be damaged severely in fire, yet the forestland will not be turned to desert or blasted wasteland. Fragile in the short run, life is tough and resilient in the long, and acts to re-establish itself in familiar patterns in surprisingly short times. Some people have spoken of dangers from overpopulation or ecological upheaval, but biologically speaking, such threats appear unconvincing. The theory is predicated on the idea that an intelligent species is an undifferentiated and passive mass, totally at the mercy of its surroundings, with all members succumbing together.

In fact, any species resembling man would possess an incredibly rich diversity of individual and cultural behavior patterns. In a time of challenge or stress, at least some of these patterns would enable them to develop, in advance, means to meet the challenge; as a biologist would say, they would be preadapted. Those cultures that truly wished to survive then could use their intelligence to learn from and adopt the ways of the preadapted ones. By a process of cultural selection, far more rapid than Darwin’s natural selection, the best new cultural forms would be proved by experience and made available to all. This is not to deny that individuals and cultures would face wrenching readjustments and difficult, often stark choices. Rather, this viewpoint denies that such cultures would perish with the old rather than adapt to the new, for such stolid inflexibility would hardly mark a species as intelligent. On our own planet, a growing worldwide trend to birth control and limited family size illustrates this point and demonstrates anew mankind’s cultural adaptability.

What of an eco-disaster or climatic upheaval? It is hard to imagine one more pervasive or far-reaching than the Ice Ages. Still, humanity survived that time quite nicely, thank you, even without modern technology, although the same was not true of the woolly mammoth or sabre-toothed tiger.

Short of a runaway greenhouse or runaway glaciation, as in Chapter 2, the worst disaster to Earth would be one that would bring widespread temperature increases to above 100°F. At such levels many animals, including man, would become infertile. Among the mammals and reptiles, it is usual for males to produce sperm in their testes, but sperm are quite delicate and sensitive to temperature. The testes must remain reasonably cool if the sperm are to avoid damage, for their proteins are subject to being denatured or broken apart by heat. In man injury would occur even if his testes were at normal body temperature, 98.6°F. It is to achieve the necessary coolness that man and other mammalian males carry their testes in a scrotum. The scrotum then dangles free and can be cooled by passing breezes.

War, overpopulation, environmental upheaval can all threaten the continued existence of species or civilizations, but none are inevitably the agents of doom, and in all there are opportunities for intelligence to avoid them entirely or to cope. Though not obvious today, eventually we may take these ideas for granted. Significantly, many people already do so and assume that intelligence even will overcome another threat: pestilence or disease. Yet human history shows this problem to have been by far the greatest threat of all, as when the Black Plague killed one-third of Europe’s people in the 1340s.

Another possibility that can easily be challenged is that if a civilization exhausted its high-grade ores and mineral resources prior to lapsing into a Dark Age, it could never again recover. Yet the steel and other materials would not have vanished into thin air; rather, the nature of the “rich ore bodies” would have changed. Instead of digging for iron ore in some version of the Mesabi Range, one would dig for fabricated iron and steel at the sites of what formerly were great cities and harbors. A single wrecked ship of fifty thousand tons would satisfy for a century the need for cast steel of a civilization at the level of Germany in the mid-1830s, which then counted thirty million people.

Moreover, we must remember that even if one intelligent species should become extinct, there may be others waiting in the evolutionary wings, ready to step forward. The rise of intelligence could take place more than once, with the earlier, failed species sending their warnings to the future in the fossil record.

Is it then truly reasonable to say that if civilizations prevail for long times, they indeed will pursue interstellar flight, interstellar colonization? Perhaps after a phase of technical advance, such cultures lose interest in exploring or expanding.

Michael Hart, whose calculations were discussed in Chapter 2, calls this idea the Contemplation Hypothesis, the idea being that such cultures pursue spiritual contemplation, not science. In a classic paper titled “An Explanation for the Absence of Extraterrestrials on Earth,” he remarked,

This might be a perfectly adequate explanation of why, in the year 600,000 B.C. the inhabitants of Vega III chose not to visit Earth. However, the Vegans of 599,000 B.C. could well be less interested in spiritual matters than their ancestors were, and more interested in space travel. A similar possibility would exist in 598,000 B.C. and so forth. Even if we assume that the Vegans always remain uninterested in space travel, there is still a problem. The Contemplation Hypothesis is not sufficient to explain [the absence of extraterrestrials] unless we assume that it will hold for every race of extraterrestrials, at every stage in their history after they achieve the ability to engage in space travel. That assumption is not plausible, however, so the Contemplation Hypothesis must be rejected as insufficient.

The same objection, however, applies to any other proposed sociological explanation. No such hypothesis is sufficient to explain [the absence] unless we can show that it will apply to every race in the Galaxy, and at every time.

There is one more possibility that deserves note: the zoo hypothesis. It holds that Earth has been set aside as an interstellar wilderness preserve akin to Tanzania’s Serengeti Plain or South Africa’s Kruger National Park. Here our evolution would proceed, our planet’s species interacting very little with the cosmic park-keepers.

This is a rather romantic notion, yet it has problems. We have our game preserves, true; but there is also such a thing as poaching on game preserves. To guard against the wily poacher requires considerable expense and effort in the administration of parks like the Kruger; in the Serengeti, less well guarded, poaching is a serious problem. In the cosmic context, “poaching” would mean the settlement or colonization of a world, in the face of efforts by a Galactic Empire to restrict or prevent such acts.

It might be that if another culture were to settle on Earth, it would do untold damage to the species here. So have our own colonists of oceanic islands done harm by bringing in rats or goats that have destroyed native birds or forests. Since planets like Earth appear to be rare, star¬farers might have a strong reluctance to take the risk of damaging our life-forms.

Is this the answer, then? Is there a system of galactic ethics whereby Earth may have been discovered but thereafter left strictly alone, with not even the asteroids colonized in view of the ever-present temptation that then would exist to venture earthward? Yet this demands a resistance to temptation, a forebearance and devotion more that of angels than of men. The existence of such worlds could not be kept secret, but would prove a continuing enticement to would-be settlers or planners of expeditions. A galactic culture could seek to guard such planets from settlement but space is vast and difficult to patrol, and there would be the age-old problem: Who guards the guardians? Even Volkspolizei on the Berlin Wall, an elite and carefully screened group, have been known to escape to the West.

Beyond this, there is a simple biochemical rule that could give the starfarers the ability to have their cake and eat it too, to settle and colonize at least small parts of a world with no fear of destroying the local species by the celestial counterparts of rats or goats.

Many biochemicals exist in two structural forms, identical in all respects save one: symmetry.
Such molecular structures are akin to a glove or shoe in that they characteristically can be described as
left-handed or right-handed. Other molecular forms are more nearly like an auto, which may have the steering wheel on the right (as in England) or left (as in America), the rest of the car being symmetrical. Even with such restricted asymmetry, though, we still describe the molecule as left-handed or right-handed.

The “handedness” of a molecular structure is established by determining its relationship to a standard molecule, glyceraldehyde, which exists in two forms. These are designated D (dextro, or right-handed) and L (levo, or left). All of life’s asymmetric molecules can be traced back and compared to this standard, which produces a very interesting result. With only trifling exceptions, all sugars, including those found in nucleic acids, follow the D-standard. All amino acids, and hence all proteins, are L-standard. [Author’s footnote: Some D-amino acids are found in the cell walls of certain bacteria, and a substance related to the sugar L-glucose exists in streptomycin.]

Why? Because this type of arrangement best suits the needs of enzymes, which govern virtually all of life’s chemical processes. Enzymes are enormously complex chemical structures, which must fit carefully to bio-molecules, as a key fits a lock. If enzymes can deal with only one of two possible asymmetric structures, their tasks are greatly simplified. An enzyme attempting to deal with the other structure would be like trying to open a door using the key upside down.

This biochemical asymmetry furnishes strong evidence for the argument that all terrestrial life has evolved from a common ancestor. There is no convincing reason why life should have been based on D-sugars and L-amino acids; most biochemists regard this primitive selection as a matter of chance. The first successful living cell followed this rule, presumably, and so it has been passed down to all, from giraffes to geraniums. Nor was there a second successful origin of life, based perhaps on L-sugars and D-amino acids. Had there been, we might now find Earth populated by two ecologies, each consisting of life forms built according to these different rules. Significantly, life forms with one system would not be able to eat forms based on the other.

Suppose a D-symmetry cat were to eat an L-symmetry mouse. Once in the cat’s stomach, the unfortunate rodent would be digested in the usual way, its body broken down to simpler substances. The sugars and amino acids would pass through the cat’s intestinal walls into the bloodstream, and then be delivered to the cells. There the problems would begin. The cells’ enzymes would not recognize the mouse’s biochemistry. The cat would fail to receive needed nourishment and would very likely suffer a severe allergic reaction. Its enzymes might find themselves stuck to the mouse’s molecules, as a wrong key will stick in a lock, and these enzymes could thus be poisoned. Some products of digestion of the mouse might build up in the cat’s bloodstream, with no easy way for their removal. In a short time one would find that while the cat had killed the mouse, the mouse then killed the cat.

If there truly were such parallel but mutually inedible communities of life, over geologic time some species might develop special enzymes that would allow them to cope with the topsy-turvy biochemistry. The species’ eventual prey would also learn to cope with the growing attentions of the predators. Instead of a sudden ecological shock, there would be plenty of time to evolve prey-predator relationships that would allow both to coexist, even in symbiosis. Naturalists know that in well-established ecologies that have evolved over a long time, the role of predators is not that of agents of wholesale slaughter. Instead, they take mostly the weak, the old, the unfit, and thus are agents of natural selection.

So if a starship commander were to seek assurance that his people could safely land, all he would have to do would be to compare biochemical standards. Since such standards are apparently a matter of chance, there would be three chances in four of his not having the same standards, both in proteins and in sugars, as the life of the new planet. His people then could land and build at least a small settlement or outpost in calm assurance that even if some of their animals were to get loose, there could be no chance of devastation of indigenous species. A stock animal that wandered into the forest would not run wild and tear up young seedlings. Instead, it would be found dead of indigestion.

We have sought to discover reasons why starfarers might not visit Earth, but in all honesty we have time and again come up with good reasons why they might. Then we recall the lack of evidence for civilizations not of our making, for fossil species from evolutionary patterns foreign to our own. And we must wonder.

Therefore, our exploration of the Fermi Paradox must end in mystery. The simple answer is to agree with Michael Hart: We have tried to explain the absence of extraterrestrials; we have reached no convincing answer. We then can only conclude that they do not exist, that we are indeed alone, unique.

The mind recoils from this. To be alone, with none like unto ourselves, is a status few would willingly accept. Yet we may find that this is the cup that has been vouchsafed to us, and from which we cannot fail to drink.

Today these questions are esoteric, academic. Tomorrow, as their full importance sinks in, they may prove to be the foundation for new science, new philosophy. The question of our relation to the Galaxy, the possibility of our uniqueness may call forth the attention that past civilizations gave to the question of our relation with God, the possibility of salvation. As Europe’s cities vied to erect cathedrals, so may future cultures build space colonies—and starships.