One of the things that makes Mars of such transcendent interest to man is the foresight it affords of the course earthly evolution is to pursue. On our own world we are able only to study our present and our past; in Mars we are able to glimpse, in some sort, our future. Different as the course of life on the two planets undoubtedly has been, the one helps, however imperfectly, to better understanding of the other.
Lowell’s fanciful theory unleashed a worldwide flood of excitement and commentary, most negative (although the nonexistence of Martian canals was not conclusively established until the Mariner satellites photographed the Martian surface at close range in the 1960s. I well remember the journalistic “hook” that Lowell’s old theory still provided; the popular press treated the Mariner expedition largely as a test for the existence of canals. As a young space enthusiast, I was disappointed, though not at all surprised, by the negative result!)
Alfred Russel Wallace was still alive and active when Lowell published his book on Martian canals—and still wielding his pen for a living. (Darwin and his friends, partially from guilt at their good fortune of inherited wealth, had secured an annual governmental pension for Wallace, but not nearly enough for a scholarly life free from financial worry.) Wallace, who had long been interested in the possibility of extraterrestrial life, and who had developed his own distinctive and idiosyncratic argument for earthly humanity as the universe’s only example of higher intelligence in bodily form, wrote an entire book to refute Lowell’s theory of canals (Is Mars Habitable? [London: Macmillan, 1907]).
Wallace mistakenly accepted the existence of canals and attempted to supply a purely physical explanation—as cracks “produced by the contraction of heated outward crust upon a cold, and therefore non-contracting interior.” Nonetheless, he offered a devastating critique of Lowell’s biological interpretation:
The one great feature of Mars which led Mr. Lowell to adopt the view of its being inhabited by a race of highly intelligent beings . . . is that of the so-called “canals”—their straightness, their enormous length, their great abundance, and their extension over the planet’s whole surface from one polar snow-cap to the other. The very immensity of this system, and its constant growth and extension during fifteen years of persistent observations, have so completely taken possession of his mind, that, after a very hasty glance at analogous facts and possibilities, he has declared them to be “non-natural,”—therefore to be works of art—therefore to necessitate the presence of highly intelligent beings who have designed and constructed them. This idea has colored or governed all his writings on the subject. The innumerable difficulties which it raises have been either ignored, or brushed aside on the flimsiest evidence. As examples, he never even discussed the totally inadequate water-supply for such world-wide irrigation, or the extreme irrationality of constructing so vast a canal-system the waste from which, by evaporation, when exposed to such desert conditions as he himself describes, would use up ten times the probable supply . . . The mere attempt to use open canals for such a purpose shows complete ignorance and stupidity in these alleged very superior beings; while it is certain that, long before half of them [the canals] were completed their failure to be of any use would have led any rational beings to cease constructing them.
Recent reports of fossil evidence for life in a Martian meteorite inspired me to retrieve the volumes of Lowell and Wallace from my bookshelf (where I had shelved them side by side—for history, among its many ironies, often places enemies in life into invariable positions of posthumous conjunction). These putative organisms of bacterial grade could not be more different from Lowell’s wise canal builders, but I was struck by a common error that both invalidates Lowell’s argument as presented above, and also underlies the fallacious main reason for public fascination with the current claim.
On August 7, 1996, NASA (the National Aeronautics and Space Administration) held a press conference to announce the publication, in the forthcoming August 16 issue of Science magazine, of a paper by David S. McKay and eight additional colleagues titled “Search for Past Life on Mars: Possible Relic Biogenic Activity in Martian Meteorite ALH84001.” In short, these scientists argued that one of the dozen known meteorites from Mars (as reliably inferred from chemical “signatures” matching Martian atmospheric and surface conditions) contained signs of life preserved in carbonate materials deposited within cracks in the rock. These cracks presumably formed and filled on Mars some 3.6 billion years ago. (The rock was dislodged by an asteroidal impact on Mars some 15 million years ago and eventually fell on an Antarctic ice field about thirteen thousand years ago.)
The controversial evidence for life does not feature such “hard” data as a shell or a bone, but consists of chemical signals in the form of isotopic ratios and mineral precipitates often formed by biological activity (but explainable in other ways), and also of minute rod- and hairlike objects looking vaguely like the smallest of earthly bacteria, but also easily interpreted as inorganic in origin. As a betting man, I would not risk any money on the case, but neither, by any means, do I dismiss the idea. The article by McKay and colleagues is a model of caution and good sense, and their case is certainly plausible for two reasons not widely enough appreciated: first, that Mars featured appropriate conditions of running water and denser atmosphere during the first billion years of its history (when the cracks of the meteorite filled with carbonate material); second, that the Earth, at the same time and under similar conditions, did evolve life of bacterial grade.
The news created the greatest flourish of public interest in a scientific topic since the eruption of Mount St. Helens. Headlines captured the front page of nearly all major newspapers. Time magazine publicly wondered whether Mars or the nomination of Dole and Kemp at the Republican convention should command the cover. They editorialized: “One of the worst things for a news magazine is a long drought of news. Almost as challenging is being hit with two stories the same week.” (They opted for the living men rather than the putative fossil bacteria, and Mars only got a corner flap of the cover, right above Jack Kemp’s head.) More locally, my phone message tape filled in less than two hours with twenty-five calls from journalists.
Our leaders erupted into rapture. Bill Clinton, with a wicked sense of timing, and hoping to steal some cosmic thunder as the Republican convention opened, held a quick press conference to proclaim: “Today Rock 84001 speaks to us across all those billions of years and millions of miles.” My dear friend Carl Sagan, who died just four months later, enthused from a hospital bed: “If the results are verified, it is a turning point in human history, suggesting that life exists not just on two planets in one paltry solar system but throughout this magnificent universe.”
A week later in our culture of sound bites and momentary celebrity, the story disappeared from public view. Invisibility quickly descended over a discovery that many commentators had anointed as the greatest scientific revolution since Copernicus and Darwin! Lord Byron spoke in Childe Harold about a “schoolboy’s tale, the wonder of an hour!” But Andy Warhol certainly placed his arty finger on the pulse of modern life by quartering the moment of attention to fifteen minutes, while extending the opportunity to everyone in an age without standards—from Kato Kaelin to poor Mr. Bobbitt, quickly cut off in more than one way.
But then, on second thought, maybe the story deserved no “legs,” and died a proper death for lack of proof and new material to sustain the news-mongers. I would like to take an intermediate position and argue that public fascination rested largely on a false premise that guaranteed an early oblivion for the story—but that a proper formulation should sustain both interest and hope for years to come.
Lowell’s logic for inferring the necessary existence of “Little Green Men” from supposed evidence of “lowly” plant life contains many errors, but none so central, or so persistent today, as the assumption that life at simplest grade must, once evolved, necessarily advance toward greater complexity and eventual consciousness. For, in such a
formulation, the origin of life in any form implies the eventual evolution of complex creatures with consciousness, so long as planetary environments remain hospitable. Thus, Lowell argued, the origin of simple vegetation unleashes a process that must lead to canal builders. Finding the “lowest” can almost be equated with guaranteeing the “highest.”
Over and over again, particularly on radio call-in programs and newspaper “man [and woman] in the street” columns, fascinated members of the public made the same mistake: if any kind of life, no matter how simple, had arisen on another world, then the evolution of consciousness must be part of a predictable natural order. (Mars became dry and frozen, thus halting the process at bacterial grade on our neighboring world. But the sequence must run to completion in many other places—for once we know that life can evolve at all on other planets, then Little Green Men must pervade the universe.)
The leading article in Time magazine began with this erroneous premise, made even worse by a false dichotomy that contrasted this supposedly inevitable scientific inference with a theological alternative:
The discovery of evidence that life may exist elsewhere in the universe raises that most profound of all human questions: why does life exist at all? Is it simply that if enough cosmic elements slop together for enough eons, eventually a molecule will form somewhere, or many somewheres, that can replicate itself over and over until it evolves into a creature that can scratch its head? Or did an all-powerful God set in motion an unfathomable process in order to give warmth and meaning to a universe that would otherwise be cold and meaningless?
May I suggest a third alternative—by far the most probable in my view (and that of most scientists), and capable of putting the recent claim for Martian life in proper perspective. If this third viewpoint were better understood and accepted, then the putative Martian fossils would enjoy far more than fifteen minutes of false and ephemeral glory, but would foster instead a sustained search for an answer to the truly vital question that Martian life at bacterial grade should inspire.
Suppose that the simplest kind of cellular life arises as a predictable result of organic chemistry and the physics of self-organizing systems wherever planets exist with the right constituents and conditions—undoubtedly a common occurrence in our vast universe, But suppose, in addition, that no predictable directions exist for life’s later development from these basic beginnings.
Evolving life must experience a vast range of possibilities, based on environmental histories so unpredictable that no realized route—the pathway to consciousness in the form of Homo sapiens or Little Green Men, for example—can be construed as a highway to heaven, but must be viewed as a tortuous track rutted with uncountable obstacles and festooned with innumerable alternative branches. Any reasonably precise repetition of our earthly route on another planet therefore becomes wildly improbable even in a trillion cases. (Since the universe must contain millions of appropriate planets, consciousness in some form—but not with the paired eyes and limbs, and the brain built of neurons in the only example we know—may evolve frequently. But if only one origin of life in a million ever leads to consciousness, then Martian bacteria most emphatically do not imply Little Green Men.)
In other words, I think that we have traditionally made the wrong division in a sequence of three steps: an appropriate planet without life (1), the origin of simplest cellular life at bacterial grade (2), and the evolution of consciousness (3). The traditional view, based on our arrogant assumption that life reaches a necessary apotheosis in creatures like us, assumes a wondrous specialness for life of any kind, and an inevitable evolution toward consciousness thereafter. Thus, the transition from 1 to 2 must be rare and onerous, but the passage from 2 to 3 easy and predictable.
Only under this false view can I understand the thrill felt by so many Earthlings at the recent report of Martian fossils. These people jumped to the false conclusion that a reported step 2, read as a near miracle of improbable advance from step 1, required nothing more than ample time to reach a fully predictable step 3—so that finding bacteria becomes tantamount to positing Little Green Men (a consummation never reached on Mars only because conditions changed, water disappeared, and “ample time” therefore failed to accrue). The only real difference between this common view and Lowell’s canals lies in our improved knowledge of Martian geological history. Lowell thought that Martian conditions, while constantly deteriorating, had remained sufficiently hospitable to permit a predictable passage to step 3—while we now know that Mars dried up far earlier, with life still caught at step 2.
But I regard this division of the three steps as deeply erroneous, and based only on our prejudice for regarding the origin of life as special, with consciousness as a guaranteed climax thereafter. Surely the easy and constantly repeated passage lies between steps 1 and 2—representing the ordinary operation of physics and chemistry under appropriate conditions—while a transition from step 2 to step 3 faces the overwhelming improbability of any particular historical path among millions of equally attainable alternatives. Life of bacterial grade may arise almost everywhere, and then usually proceed nowhere in particular, if anywhere at all—a perfectly splendid outcome since bacteria dominate nearly all environments of life on earth even today. We now live, as Earth always has (see my 1996 book Full House), in an Age of Bacteria. These simplest organisms will dominate our planet (if conditions remain hospitable for life at all) until the sun explodes. During our current, and undoubtedly brief, geological moment, they watch with appropriate amusement as we strut and fret our hour upon the stage. For we are, to them, only transient and delectable islands ripe for potential exploitation.
If we could make this readjustment to view Homo sapiens as an ultimate in oddball rarity, and life at bacterial grade as the common expression of a universal phenomenon, then we could finally ask the truly fascinating question raised by the prospect of Martian fossils. If life originates as a general property of the material universe under certain conditions (probably often realized), then how much can the basic structure and constitution of life vary from place to independent place? We simply cannot answer this question from the only “sample” we know—life on earth—and for an interesting reason arising from the core of scientific method.
All life on earth—everything from bacteria to mushrooms to hippos—shares an astonishing range of detailed biochemical similarities, including the structure of heredity in DNA and RNA, and the universal use of ATP as an energy-storing compound. Two possible scenarios, with markedly different implications for the nature of life, might explain these regularities: either all earthly life shares these features because no other chemistry can work, or these similarities only record the common descent of all organisms on earth from a single origin that happened to feature this chemistry as one possibility among many. In the first case, life on other worlds will independently evolve the same chemistry as a sole viable choice; in the second case, other living systems may feature a wide range of alternate chemistries.
We cannot ask a more important question about the nature of life. But, ironically, we also cannot begin to answer this question with the data now at our disposal. Above all, experimental science requires repetition to test the predictability of outcomes. If a phenomenon happens only once, we simply cannot know whether the properties we observe must exist as we find them, or whether other “replays” might yield markedly different results.
Unfortunately, all life on earth—the only life we know—represents, for all its current variety, the results of a single experiment, for every earthly species evolved from the common ancestry of a single origin. We desperately need a repetition of the experiment (several would be even better, but let’s not be greedy!) in order to make a judgment.
Mars represents our first real hope for a second experiment—the sine qua non for any proper answer to the question of questions. Unless earthly and Martian life share a single origin by seeding from a common source—an obvious possibility if Martian fossils can re
ach Earth by meteoritic impact!—then any life on Mars fills the holy grail of our ultimately precious second experiment.
Ancient Martian fossils will not yield the required evidence, for we need living matter with intact biochemistry, ripe for reading either as DNA, or as a workable alternative as yet unimagined by students of earthly life.
The Martian surface may now be cold, dry, and dead. But, on our planet, bacteria can live in pore spaces within rocks several miles below the earth’s surface, so long as water percolates through. A similar subterranean environment on Mars may still feature water in liquid form. Thus, if life at bacterial grade ever evolved on Mars, these organisms almost surely disappeared from the Martian surface long ago, but may still live within the more hospitable environment of subsurface rocks. The putative fossils from Mars provide our greatest reason for hope that the second experiment still lies buried, but very much alive, beneath the surface of our sister planet.
So let us send forth our robots, and perhaps (eventually) even our persons, to look, find, and return—for this experiment can be done! Forget those Little Green Men, those nonexistent canal builders, those fantasies recently unleashed under the false belief that ancient bacteria imply the eventual evolution of consciousness. The simplest life may pervade the cosmos, and a second independent sample may answer the riddle of the ages. Let us use our distinct and oddball intelligence to track down any direct evidence for the range of life’s universal structure. The next step from our sun—the most accessible of all other planets—may yield a ready answer. The host of the cosmic bacterial manifold, the dominant beings who mocked Lowell for thinking that his kind rather than their kind might pervade the universe, may then smile with satisfaction and say, “So you finally understand; well done, thou good and faithful servant.”
Leonardo’s Mountain of Clams and the Diet of Worms Page 33
