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William H. Calvin
This page is at http://WilliamCalvin.com/bk3/bk3day8.htm
The River That Flows Uphill (Sierra Club Books 1987) is my river diary of a two-week whitewater trip through the bottom of the Grand Canyon, discussing everything from the Big Bang to the Big Brain. It became a bestseller in German translation in 1995. AVAILABILITY limited; the US edition is now out of print. There are German and Dutch translations in print.
The River That Flows Uphill
A Journey from the Big Bang
to the Big Brain

Copyright 1986 by William H. Calvin.

You may download this for personal reading but may not redistribute or archive without permission (exception: teachers should feel free to print out a chapter and photocopy it for students).

This is a Deluxe edition in an unusual sense: the photographs and sound files are from Leonard Thurman’s Grand Canyon River Running web pages. What you get on your web browser is assembled, before your very eyes, using text delivered from Seattle (Washington State USA, near the Canadian border), and pictures and sound being sent from Tucson (Arizona USA, near the Mexican border).


It is unwise... to assert that evolution could not have done this or must have done that, except in the broadest possible terms. It is a good working rule for the biologist that evolution is a lot cleverer than he is.
......the molecular biologist Francis H. C. CRICK, 1979

Mile 120
Blacktail Canyon

CLONING DOES ALLOW FOR VIRGIN BIRTHS which, as Cam pointed out at breakfast, ought to make some people happy.

"You know how virgin births came about, don't you?" asked Ben. "I mean, in religion?"

"It's an Old Testament prophecy, from way back, many centuries before Christ," Rosalie replied.

"Well, in the original Hebrew, it said something about a young woman giving birth to a prophet," Ben said, sipping his tea. "But by the second century B.C. in Alexandria, Hebrew was getting to be like Church Latin -- not too many people could read it. The educated people all knew Greek, so to promote their religion, the religious scholars translated the Old Testament from Hebrew to Greek. The only trouble was that in the process, they translated the Hebrew phrase for 'young woman' using the Greek word for 'virgin'."

We laughed. "That's one little translation error that really started something," Cam replied, chuckling.

"I heard of another Hebrew translation error," Jackie volunteered. "Well, maybe not an error but a little problem of double meanings. You know about how women are supposed to give birth 'in pain'? The original Hebrew word in that passage of the Bible is b'etzev. Now, one meaning of that is pain. But the other common meaning one would translate as 'in sadness.' So maybe that Biblical passage isn't about the pain of childbirth -- maybe it's an early description of postpartum depression?"

CONQUISTADOR AISLE is a long straight stretch of river just down from Blacktail, with the Muav on the right bank creating sculptures much like Gray Castle back in the Photogenic Fifties. These scallops look like an oblique view of a row of chessmen, lined up before the match starts, extending into the distance.

One of the first rapids here is another of those "No Name Rapids" -- at least in the eyes of the boatmen and the authors of river guides. Imagine the surprise our boatmen got when they looked at the American Automobile Association's otherwise excellent road map "Indian Country" and found that this rapid had been given a name that no one on the river had ever heard of -- Enyeart Rapid. I suspect that the AAA threw in a fake name, in the abominable manner of map-makers generally, to serve as a tipoff if someone copied their copyrighted map -- while, of course, confusing everyone else. Intentional lies in a reference work are most offensive. One never knows where they'll lead.

Naming an unnamed rapid, however, is less hazardous than adding a road or bridge that doesn't exist, which is what paranoid map-makers often do. I once discovered, on an official government map for pilots, where a road had been added around the northwest side of Mount Rainier in Washington State, connecting the dead-end West Side Road with the dead-end Mowich Road. Such a grand loop road, I am happy to report, does not and never has existed; I wrote the Federal Aviation Administration and asked them to remove it from that map as a hazard to lost pilots trying to follow a road back to civilization. And then I got to thinking: maybe it's another copyright ringer? But why would the government bother to do this, since anyone is free to copy their maps? Or did the government mapmakers get lazy and copy an oil company's maliciously mangled map when they made the pilot's map, transcribing the nonexistent road? Of course, perhaps (the wilderness hiker's paranoia) they're just planning to build yet another road through the remaining wilderness.

About two-thirds of the way down Conquistador Aisle, there is a side canyon on the right which has an excellent natural amphitheater. The music trip sometimes stops here, and the boatmen haul the cello several miles into a charmed place called the Delphic Amphitheater.

COWARDS ARE THE BASIS OF CIVILIZATION, it says somewhere. That's because cooperation -- you go first, but reciprocate next time, please -- needed some way to get rolling, some way in which an animal could gain long-term advantages while enduring short-term disadvantages.

Many species have rules for helping to minimize conflicts, allowing something else to decide who gets the reward (simple conflict-avoidance rules -- such as deferring to whomever arrived first -- are seen even in butterflies). And there are individuals -- call them "doves" if you like -- who avoid conflicts with others of their species. When challenged for possession of a choice resource, doves prefer to avoid the costs of losing a fight and wait for another chance at the rewards. The opposite type lets no one get in the way of immediate rewards; this "hawk" naturally spends a lot of time and energy fighting other individuals, risking injury but also wasting time that could otherwise be used in searching for other food.

I suppose that if every individual were a hawk and the food were concentrated in one place, most would be injured fighting over food. One might expect there to be some optimal ratio of hawks and doves for a species, just enough hawks so that they encounter doves more often than other hawks, enough doves so that they usually get to eat before a hawk arrives to contest their meal. In fact, one can even predict the ratio of hawks to doves by knowing the relative costs of each alternative. Costs here might be measured in calories: how many calories in the food, how many calories spent searching for food, how many calories wasted fighting, how many calories burned while waiting for another chance, and the costs of injury and disability. For a given set of reasonable numbers, one might wind up with a 30:70 hawk/dove ratio. Note that being born a dove into an all-hawk society can be an advantage -- you may lose every encounter and get to eat only when uncontested, but you won't suffer the costs of fighting and can potentially be better off than everyone else.

This hawk/dove strategy can yield a stable ratio: if one starts with a 50:50 ratio, enough hawks will die so that the ratio becomes 30:70; if one starts with too many doves, the hawks will out-reproduce them until a 30:70 ratio is achieved. This situation is an element of the evolutionary stable strategy or, as it is known in evolutionary biology, an ESS. The only way that the 30:70 ratio can be changed is to modify the relative payoffs, and even that may exhibit a stability that confounds permanent change. However, suppose you play dove most of the time and hawk some of the time? What would happen if you played hawk in dealing with an individual who usurped your rightful due the last time, but played "after-you" otherwise, taking your turn when it came. Might such simple cooperation work better than the hawk/dove strategy's payoffs?

Yes, but there are many variants on cooperation, and some work better than others. Some are not evolutionary stable strategies -- should some hawks invade, they could wipe out the cooperators. Still other strategies are just not stable, with the population fluctuating in a boom-or-bust manner.

Take the simple matter of paying back cheaters, playing hawk with cheaters who don't take their turn when they should. If one plays hawk forever with such a defaulter, the population will soon become locked into a rigid collection of hawks. So that perpetual suspicion strategy is unstable, degenerating into the stable hawk/dove extremes with its poorer payoffs, the niche supporting fewer individuals. There is a virtue to forgiveness, to again cooperating once you've paid them back for cheating.

That is one conclusion of a big contest between computer simulations that tested various strategies for cooperation. A simple strategy called "tit for tat" was the winner: you initially cooperate when encountering a new individual, then expect them to reciprocate (or whatever the cooperation strategy is). If they cheat, you play hawk next time and pay them back. Then you forget about it, returning to cooperation. The animals in tit-for-tat need the ability to recognize one another as individuals, a memory that lasts until the next possible encounter, enough hawk in them to play the role on occasion, but that's about all -- no altruistic nature, no higher thoughts about how it would be much better for everyone if we all just took turns. Tit-for-tat is one of the viable variants on the hawk/dove theme; an evolutionarily stable strategy which -- provided those calorie ratios don't sink below certain critical values -- will survive even if the cooperators are invaded by pure hawks. Tit-for-tat is a robust strategy, in that many different calorie payoff alternatives will work with it.

Most importantly, it will survive once established -- as the economist Robert Alexrod and the theoretical biologist William D. Hamilton said, "the gear wheels of social evolution have a ratchet." It would be easiest for the "genes for cooperation" to develop in small groups -- perhaps on a tropical island, where everyone is a close relative anyway, and where making a living is easy enough that one doesn't starve if they allow someone else to go first. Once an individual bearing the "cooperation genes" migrates elsewhere (I like the proverbial farm boy moving to the big city), he will encounter many cheaters. He'll lose to them only once, because tit-for-taters have good memories. Whenever he interacts with someone with the cooperativity genes who will indeed alternate with him, then the advantages of cooperation will manifest themselves in the increased payoffs. Thus, even though the payoff is reduced in the new environment, the cooperation genes won't necessarily be wiped out. Their population will grow, relative to all the pure hawks and doves, because of the more efficient food gathering and conflict avoidance they produce.

Via such a scenario, tit-for-tat (or something like it) could have engendered cooperation on a large scale: cooperation was a variant that found a niche and was preserved by evolutionary processes of selection and speciation. It was another emergent principle, a surprise consequence of some simple properties of memory and behavior, but one with far-ranging implications for the evolution of social species like ours (and the insects, and the dogs, etc.). We may now use strategies far more complex than the childish tit-for-tat, but cooperation got started somehow.

And now game theory -- that mathematical subject that has been applied to both chess and war games -- has shown evolutionary biologists one of the possible ways cooperation evolved by focusing our attention on the minimal set of rules necessary to move beyond hawks and doves. The cooperation genes may, of course, be little more than the genes for a brain that can recognize a large number of separate individuals, genes that produce enough body shapes and colors to create discernible individuals, genes that provide a memory good enough to pay back a cheater (but not too good, so as to get stuck playing the hawk forever!), and something to soften unconditional hawkishness (a bit, indeed, of the coward).

If cooperation is a variant along some hawk/dove continuum, we might expect a cooperating species to still contain a certain number of individuals who fall into the hawk or dove extremes. If this scenario for the evolution of cooperation is even half true, then the unusually timid and the sociopath are living reminders of our evolutionary past -- and a reminder that variation still prevails, is still being industriously created by those busy permutations during crossing-over.

While we may have started with such a simple set of rules, happily emerging into an evolutionarily stable strategy encoded in our genes, we will probably have to create a far more complicated strategy to stay alive. Playing tit-for-tat in a nuclear age is far worse than merely childish, yet our national leaders mouth platitudes which suggest such simple-minded thinking.

To be wronged is nothing unless
you continue to remember it.

Without forgiveness life is governed by... an endless cycle of resentment and retaliation.

Mile 127
Middle Granite Gorge

EARLIER WE NOTICED that the Tapeats ledges were going downhill, as if they were planning on disappearing into the river, reversing their appearing act back in the Fifties. But they stopped, and now we see the Tapeats emerging again, more and higher sandstone ledges surrounding the river channel.

Soon schist appears again, and we once more cross the Great Unconformity, though without the salt mines this time. Unlike the tunnel-like abrupt appearance of schists back at Mile 77, this emergence is gradual in the manner of the other layers. We are entering the Middle Gorge, back in the schists again; Major Powell's expedition was none too pleased to see the schists reappear, given the big rapids that followed their original introduction to them. At least here there are no big rapids, no V-shaped illusions of plunging into an abyss.

But the black marble effect is much greater here: really black and highly polished. And an anomaly: here we see a polished black layer atop a dull schist layer. Now the bottom layer really should get more river polishing than the higher layer. Oops.

After some discussion we decided that the higher one must be a different type of schist, one that takes a shine better. Indeed, the guide book says it is called hacatite and that it is a metamorphosed basalt of volcanic origin; the dull stuff is sandstone and siltstone that has been metamorphosed instead.

There is a virtual row of trees on the right bank, one story above the river; they seem to form a green line along the bottom of the talus slopes. This is another little illustration of evolution in action: the trees that grow below the high water line get washed away in the floods. Those variants with long roots, which also happened to take root up away from the river, are what remain after natural selection. If you want a variety of riparian tree with extra-long roots, come and borrow a few seeds from these trees: evolution has been at work on them.

Strangely, the river is heading northeast, back in the direction from which we came a week ago. This is no mere meander. We can't continue west because Great Thumb Plateau looms ahead of us to the north and west. It's part of the South Rim -- to the north of us! And the North Rim -- in the form of Powell Plateau -- is now south of us. In its early editions, the blue bible's river map for this section of the Canyon had the North arrow pointing the wrong direction -- the artist must have decided that the South Rim was to the south. But only on the average, just as rivers flow downhill on the average but can appear to run uphill when one is watching a big back-eddy. All those variations from the average certainly do make things interesting.

LIFE IS CHANCY, to be sure, but it is still a surprise to find that nature has also gone out of its way to shuffle the deck. The average, even the nominal variations, appear not to be what nature emphasizes. With each generation, crossing-over introduces new noise even if point mutations don't.

Taken by itself, all this randomness seems like noise intentionally introduced into a well-tuned radio -- like static, pops and crackles superimposed upon music, like stray notes being struck while playing the harmonic inventions of Bach. The Goldberg Variations would be ruined. We recoil from the notion, just as did Darwin's critics -- and they didn't know even the tip of the iceberg about how randomness seems to be the name of the game. After all, we try to engineer quiet hi-fi amplifiers, reliable cars, predictable spare parts. What Creator would intentionally make her creation creaky?

And now it turns out that sex is all about increasing the noise, by intentionally shuffling the carefully preserved genetic instructions for how to construct a new body and brain. As if mutations weren't enough, and more randomness was needed. So scramble the blueprints a little. Mutations evolved a system for permutations -- and that was a big step in evolution. It institutionalized randomness.

"THINK RANDOM" would, I suppose, be an appropriate sign to hang over the desk of the evolutionary biologist, though I doubt that this slogan will ever catch on because of the bad press that "random" has had. It would seem like an exhortation to woolly-headed thinking, to promoting disorder, incomprehensibility, chaos.

This nomenclature problem has been faced before, by mathematical theorists. They, of course, are quite used to the regularities that may occur in the superstructure of a noisy process; though the motion of an individual oxygen molecule in the air may seem quite random, winds do exist. There is even a whole branch of mathematics called the Theory of Random Variables. And so a near-synonym for "random" has developed which, because it is thoroughly Greek to everyone, lacks the unfortunate connotations of randomness. Thus, one reads up on the Theory of Stochastic Processes only to find good old random variables being slung around again. If a T-shirt exhortation to evolutionary thinkers is ever produced, I predict that it too will read "THINK STOCHASTIC!"

This puzzling randomness cannot be understood by itself, in isolation from the other mechanisms involved in evolution: selection pressures such as disease and late winter snows, temporary barriers such as rivers, and permanent barriers such as speciation from shifts in mating seasons. Only in context does the randomness begin to make sense -- if one looks at it long enough and hard enough.

The challenge of Darwinism is to find out what our genes have been up to and to make that knowledge widely available as a part of the environment in which each of us develops and lives so that we can decide for ourselves, quite deliberately, to what extent we wish to go along.

...the more we discover about the mechanisms of genetic control, the better equipped we will be to escape those controls through an enhanced awareness, to transcend them so that we may, for the first time in our history, work for ourselves instead of our genes, exercise truly free will and free choice, give free reign to our minds and spirits, attain something close to our full humanhood.
......A. ROSENFELD, 1977.

I CALLED THE CREATOR "SHE" for some good biological reasons, not just equal time. You even inherit more than half your genes from your mother -- you may get half of the DNA in your cell's nuclei from your father but all your mitochondria (the powerhouse of the cell with its own DNA and separate genetic code) come from your mother. You see, the sperm's mitochondria seldom make it into the ovum at fertilization.

Males are the oddballs, not being able to directly reproduce themselves (the females of some species can clone themselves if males are scarce or unsuitable). And we mammals all start off as female in utero; it's only later in prenatal development, when the Y chromosome causes extra testosterone to be produced, that female genitalia are modified into male ones.

There is some evidence that this male afterthought wasn't as well engineered as the female original. Males are more liable to birth defects. Boys die in childhood more readily than girls. Adult males are likely to start falling apart at an earlier age than females. Rather than Eve being metaphorically made from Adam, biology suggests that it should be stated the other way around -- if at all.

SEX HAD TO EVOLVE TOO; this institutionalized randomness wasn't present at the Creation. Somehow, the crossing-over shuffle of the genome was superimposed upon ordinary cell division -- but only in some specialized cells, those of the so-called "germ cell line," a fancy name ("germ" as in germination, not pathogens) for the cells that produce sperm and eggs. What, one might ask, would be the immediate advantages to the organism of such an additional complication? Sure, it's better in the long run for the evolution of more complex organisms (like us), but what on earth was the immediate short-run advantage? How was the ratchet run by selection and speciation to create a sexually reproducing organism in the first place?

Indeed, there is a serious disadvantage to sex that must be overcome in the short-run. Namely, males. Sex tends to produce numerous individuals (often half of the total) who cannot themselves give birth. It reminds one of the insects which almost ruined Darwin's theory for him. Those sterile castes of social insects (ants, wasps, bees) seem to have evolved only because selection sometimes acts on groups of individuals, rather than on each individual in isolation, and the sterile ones enhance the success of their sisters who do reproduce. That suggests that males can exist because they make the actual reproducers, the females, much more than twice as successful in getting offspring to reproductive age themselves. Now in advanced organisms such as frogs and birds, the male's efforts at brooding the young may improve the survival rate. But I suspect we may have to look to something more elementary, something that will work in simple organisms. Something that directly involves the increased randomness generated by sex. STOCHASTIC SEX -- I can see it now, emblazoned on the students' T-shirts. And misinterpreted by most of the people who see it.

While sex in eukaryotic cells got started about 1,000-million years ago, there is an even more ancient form of sex in bacteria, in which cells exchange some genetic material without fusing. And the virus, that little packet of DNA that lacks the usual cell machinery for protein synthesis, is perhaps another one of the original ways of mixing up genes a bit. Often looking like a moon-lander with a hypodermic needle protruding, the virus goes and, kamikaze-like, injects its RNA or DNA into a proper cell, even committing suicide as a means of producing more viruses. So crossing-over as we practice it is only a more recent version of what may be a variability scheme over 2,000-million years old. So we should not look solely at multicellular levels of evolution for the explanations of sex, but seek clues from more elementary cases of mixing things up.

Various schemes for the evolution of sex have been proposed, and have been given such catchy names as the "Red Queen Hypothesis" and "Pathogen Escape." The first takes its title from From the Looking Glass in which the Red Queen tells Alice that she has to run as fast as she can just to stay in the same place. The arms race of this century has brought the Red Queen's quip into focus, a sobering reality. But the arms race is also a succinct way of summarizing the tendency of ecosystems to keep getting fancier rather than attaining a truly static "balance of nature": a plant that is eaten by an insect develops better defenses such as becoming toxic, the insect develops better ways of inactivating the toxin, so the plant raises the ante and the arms race continues. To keep up with the plant's ability to vary its defenses, the insect has to produce a variety of offspring, some of which will be able to cope with the changed conditions. The Red Queen Hypothesis says that the increased variability in offspring produced by sex had an immediate advantage, because some of the offspring could become much more successful than the run-of-the-mill nonsexual offspring who could only hope for a lucky mutation to strike.

While the Red Queen hypothesis focuses on exploiting resources better, the Pathogen Escape hypothesis looks at one of the main sources of illness and mortality (which do tend to limit one's reproductive abilities): being inhabited by a parasite, or having your genetic machinery borrowed by a virus, or having your internal environment utilized by too many bacteria for their own ends.

Cells have ways of defending themselves against exploitation by pathogens, and multicellular organisms like ourselves have specialized cells assigned the job of cleaning out invaders that lack the right passwords -- recognition signals in the form of proteins embedded in their cell surfaces. These defender cells are specialized to recognize different foreign proteins; when they find a protein "lock" that matches up with their "key", they kill the offending cell. The defender cell not only destroys but reproduces itself in the process, making even more defender cells of that type. This is how the body fights infection; after the infection is over, it has a lot of defenders for that particular foreign cell and so makes a subsequent infection much less likely to succeed. This is how we acquire immunity to, say, the Asian flu virus. Immunization usually consists of stimulating the antibody-production mechanism without precipitating a major infection. Minor infections are sometimes good for you.

The defender cells in an individual's bloodstream are thus a history book of his exposure to infections, if one knows how to read it. There are six major variants on the Asian flu virus; many old people have, circulating in their bloodstream, defenders against all of six types. Each is left over from an exposure to one of the flu subtype (some of which may not have caused obvious illness but instead a subclinical "silent" infection that stimulated the immune system to produce more defenders). Children's blood will have defenders only against the strain of flu virus that has most recently been around.

By piecing together the pattern of defender cell types present in people of various ages, it can be seen that Asian flu subtype A5 was the one responsible for the epidemic of 1918, that subtype A0 occurred in 1933, subtype A1 in 1946. The 1957 epidemic was caused by subtype A2, which was last seen in 1889; the "Hong Kong" epidemic of 1968 was subtype A3, same as in 1900, and subtype A4 in 1978 was the same as in 1910. This suggests that we'll be back to subtype A5 before 1990. This hypercycle, as it is called, takes 68 years -- about the average human life span for those who survive childhood. Since most of the people alive in 1990 won't have had the flu in 1918 and thus have acquired cells to fight A5, subtype A5 should have more success in 1990 than it would have had in 1970. Just like the "17-year cicadas" whose reproductive cycle is a prime number of years so that they can escape predators with shorter life cycles (yes, I'm afraid that evolution invented prime numbers too), the Asian flu virus outsmarts the human immune system with a longer cycle; with the recent increase in average human lifespan, it will be interesting to see if the Asian flu will falter.

Pathogen Escape concerns how you develop defenders against, for example, subtype A4 after being infected. Your genes cannot possibly carry the code for every conceivable foreign protein that might work its way into your body, and then produce defender cells for each type; there just isn't room for so much information in the cell nucleus. I don't know if the following story will turn out to be true or not, but it illustrates how the immune system could work, using only simple rules.

Suppose that (at some developmental stage, not necessarily always) a defender cell had, on its surface, the same protein that the cell attacked, sort of a lock and a key on opposite sides of the cell surface. This means that identical cells would tend to attack one another. Soon one would have a population of defender cells that were all different, a very simple self-organizing system emphasizing diversity. Suppose further that defender cells divided when they successfully attacked (just as when building up immunity) -- but that they sometimes mutated in the process, making a slightly different password protein. Maybe they shuffle the genes as happens in crossing over? If the mutation happened to produce a protein on the cell surface identical to the one coded for by an existing defender -- well, too bad. But if it produced a unique password protein, such a new defender cell would enjoy a long life. There would wind up being a massively diverse population of defenders, coding for far more invader types than the original genes could have done.

As I said, whether true or not, this example shows how a very capable system can arise from two simple rules: competition between identical cells, and an occasional random mutation. As I thought about it a little more, floating down the river, I realized that this shuffling and elimination need only happen in a setup period during prenatal development. Once the diverse password population was produced, the immune system could settle into a postnatal mode without further mutations or permutations.

And that has some advantages when one considers how to prevent my immune system from attacking my own proteins -- what is called the self-recognition problem. Such attacks during the setup period -- when so many of my own proteins are being produced that losing a few to defender cells won't matter much -- wouldn't be a problem. Sure, I'd lose some structural proteins but the defender type might not reproduce as well without two defender cells involved (this is similar to the sterile male strategy for controlling insect pests). This means that when the mutation mechanism was later turned off by development, I'd have hardly any defender cell types corresponding to my own proteins. So I'd wind up with a broad spectrum of defender cells, far wider than any coded by my genes, yet the ones corresponding to my particular body's proteins would have been eliminated during the setup period. If something goes wrong with this sequence, of course, my immune system might start attacking me successfully in adult life, when I don't have so many structural proteins to spare (the production rate for many types of proteins drops dramatically between the ages of 20 and 70). This provides a model for "autoimmune" diseases such as lupus, myasthenia gravis, rheumatoid arthritis, and juvenile-onset diabetes, in all of which the body's self-recognition mechanism seems to fail.

So a gene-shuffling mechanism might have been handy in the immune system, enabling the organism to better survive infections by producing a broad range of defenders. Maybe escaping pathogens is what selected the gene shuffler, but the shuffler in turn may also have affected those cell divisions producing sperm and ova -- and created recombination and crossing-over. If true, it was a sidestep in evolution -- sex succeeded because its shuffling mechanism was a gift from the immune system.

While life on the individual level is indeed chancy, evolutionary processes have been enthroned randomness as a virtue, and all because it turned out to be so handy in the short-run for gaining a temporary advantage in the "propagate-your-genes" sweepstakes. Its long-term advantage, of progressively more intricate organisms such as ourselves, may be another one of those emergent principles -- a free bonus for more elementary efficiencies.

The effect of a cause is inevitable, invariable and predictable. But the initiative that is taken by one or other of the live parties to an encounter, is not a cause; it is a challenge. Its consequence is not an effect; it is a response. Challenge-and-response resembles cause-and-effect only in standing for a sequence of events. The character of the sequence is not the same. Unlike the effect of a cause, the response to a challenge is not predetermined, is not necessarily uniform in all cases, and is therefore intrinsically unpredictable.
......ARNOLD J. TOYNBEE, A Study of History

If our kind of mind had been confronted with designing a [DNA-type] replicating molecule, starting from scratch, we'd never have succeeded. We would have made one fatal mistake: our molecule would have been perfect.... The capacity to blunder slightly is the real marvel of DNA. Without this special attribute, we would still be anaerobic bacteria and there would be no music.
......LEWIS THOMAS, The Medusa and the Snail, 1979.

Mile 132
Stone Creek

HARD ROCK THAT COMES UNRAVELED? There is some fascinating rock around here which shows asbestos formed from contact metamorphism. When some crystalline basaltic rocks are overheated, simply by being in contact with a very hot substance, the subsequent cooling can produce fine crystalline fibers between the hotter and cooler regions. And so you can pick up a rock and see a white band very different from all the rest. Using a fingernail, you can pull off little white filaments. Asbestos is handy for insulation against heat (if you can avoid breathing and drinking it); it used to be the best thing around. Several miles downstream from the sandal race this morning, there is an old asbestos mine that provided some of the long asbestos fibers used to make fire curtains for theatres in Europe, back at the turn of the century.

The long stretch of sandy beach here at Stone Creek is washed clean by the artificial tides every 24 hours. We are stopped here because Alan wants to take us for a beach walk. Sea shells? Here? No, Alan is preparing the beach, implanting sticks and drawing lines as he paces off distances.

Well, we are also stopped here for lunch, having just gotten soaked in Deubendorff Rapid, an 8. Alan is munching on an oversize sandwich as he paces along the beach, counting his steps, then stopping and drawing yet another line in the sand. Or planting a stick. Even making a little sand castle. Marsha is following along, asking questions. But Alan manages to keep his mouth too full to talk, and so she stews in suspense as he keeps muttering "Just a minute, just another minute. Gotta count." And he keeps pacing off the distance. What distance? The rest of us wonder, as we head back for seconds on lunch. Hard work, running rapids.

Finally -- for dessert, as he puts it -- Alan invites us all over for a little "walk through time." We first hike all the way down to the far end of the beach, more than a city block, where Alan has constructed his first sand castle. As we stroll down to the starting place, I am reminded of Alan's other famous walk: one winter, he and two friends started off 60 kilometers north of the North Rim, using cross-country skis through the forest up to the snowbound visitor center perched on the rim, then carried their skis as they hiked down to the bottom of the Canyon (the skis were certainly a novelty down at Phantom Ranch) and up the trail to the South Rim. Then another time, they hiked from Phantom up, and walked 50 kilometers south to climb Mt. Humphreys, the tallest of the volcanic peaks behind Flagstaff. From 2,700 meters elevation, down to 600, then up to 3,800. Alan's walks are ambitious.

"Now this here," began Alan, "is when the solar system went into business about 5 billion years ago, when the collapsing dust cloud finally got hot enough to ignite a thermonuclear reaction and, lo, the sun began to shine. And up there at the lunch table is the present time, today to be exact. And we're going to walk all the way through the earth's history. Now if you want to go all the way back to the Big Bang and work your way through the formation of elements and the local supernova that seeded the dust cloud that started this here sun," he said, pointing to the round sand castle at his feet, "you'll have to swim another 10 billion years upstream before you reach the Big Bang."

"How do we pace off the distance if we can't walk on the bottom of the river?", Marsha asked.

"Details, details. Now on the scale I've picked, one standard pace -- my kind, anyway -- is equal to 50 million years. All the way back up to the picnic table is 100 paces. Five billion years -- call it 5,000-million for simplicity, since we'll deal in million-year units, just like the Anasazi probably thought in units of lunar months. Just to give you some idea of speed, it'd take about one pace for all that fifty stories of Redwall cliff to be laid down." He pointed up at the Redwall across the river. That's one percent of the total?

"Well, now, we walk 8 paces, up to 4,600-million years ago, and the earth has finally condensed out of all that dust swirling around the sun, probably focusing around an eddy that formed in the disk of dust."

"Now just remember that," interjected J.B. "Back-eddies are useful."

"Another 22 paces," Alan resumed, "and we reach 3,500-million years ago, when the earliest known traces of life forms have been found." He gestured backward. "You just walked through the transition between physics and biology. Now those 22 little steps cover a mighty important period, when all those volcanos, and lightning, and ultraviolet light were making carbon compounds. Methane was in the air. Probably stank too, though there wasn't anything around to smell it -- now that, in my humble opinion, is the right way to do real organic chemistry. It rained, and rivers flowed, and the rocks got sorted into piles of big rocks and little rocks, even clay to catalyze the organic reactions. So here we are, almost a third of the distance covered, and finally organic chemistry has gotten to be a real self-organizing system that could presumably replicate itself. That is to say," and Alan drew the letters in the sand next to his sand castle with a leaf for a flag, "'Life began'."

"So were DNA and the genetic code invented before then?", asked Cam.

"Until someone discovers otherwise," mused Alan, "that's the assumption. So the seas swelled with cells that had no predators -- and the main food they ate was sunlight. Not too different from what all those phytoplankton do in the oceans today, making most of the oxygen we breathe -- excepting, of course, that they now get eaten by everything from zooplankton to whales.

Alan started walking again. "The important thing happening now -- with of course, our parochial hindsight, is that photosynthesis was churning away, throwing away oxygen in the same way that we discard carbon dioxide. Since the oceans couldn't hold any more after about our first step, or 50-million years, the atmosphere became the big dumping ground for all that useless oxygen. Twenty-nine, thirty. By about here, at 2,000-million years ago" and Alan stopped at his second stick, "our present 20 percent oxygen atmosphere was complete. It took 1,500-million years to develop, and the reason it took so long is that all the exposed iron and silicon and whatnot on the earth's surface happily gobbled up any oxygen they could snatch out of the air. That's why the Redwall's red -- good old rust. So until everything was rusted, the oxygen percentage stayed pretty low. So there you see," and Alan pointed up to the Redwall once again, "what used the oxygen before we did."

He kicked the sand underfoot. "So here we are, already more than halfway from the start of the Earth to the present, and we're just getting the oxygen atmosphere that our kind of life requires. And now a whole new ballgame starts. What's next, baseball fans?"

"How about bacteria finally coming up with a nucleated cell?", volunteered Ben. "You know, a nice storehouse for all that genetic code, instead of scattering it around the cell like those simple-minded bacteria do? Supercell?"

"Sold," said Alan, and started marching 14 more steps, up to 1,300-million years ago. "Now that's moving. We're finally up to the age of some of that Vishnu Schist you've been seeing again on the river this morning. And there were now fancy cells on the scene, with all sorts of specialized little internal factories like mitochondria and chloroplasts for energy, regular little powerhouses. All those good things. Supercell has arrived," he said, planting a third stick in the sand. "And nearly three-quarters of the time is already gone."

"You're going to have to speed up if you're going to get this all finished in seven days," Cam needled.

"That's all right -- evolution's about to go into high gear." Alan gazed back upon his work. "Now just look at that. It took a whole 1,100-million years -- 22 paces -- just to get cells going. Then it takes twice that time again before you finally get Supercell." Then he swiveled around to look ahead. "But it'll only take a few-hundred-million more years to get colonies of cells living together, making multicellular organisms. Sex probably started here about 1,000-million years ago. And those cells started becoming specialized. Some handled only digestion, while others took care of sensation but got fed by some specialized truckers, transporting cells that carry the goodies in between a gut cell and a sensory cell. Now that's real progress." Alan paced up to 600-million years, completing seven-eighths of the total span of time on Earth.

"And finally here you get an explosion of life, particularly life with specialized cells that build strong shells by oozing out some calcium compounds. Which leave nice fossils for us to find. Thus marks the end of the pre-Cambrian era."

"We also just walked through the Great Unconformity," noted Marsha.

"Give that girl a gold star," announced Alan. "There is indeed a lot of rock missing from that period, leastwise around here. Our Tapeats Sandstone over there is from the Cambrian, this period starting maybe 570-million years ago when the fossils become abundant. And they're not just of one kind of organism, but all sorts of plants and animals, as if a lot had been going on back in that last section that we never saw -- not because there's a Great Unconformity everywhere, but because it just plain didn't leave many fossils. Some microfossils, to be sure, and paleontologists are finding more and more. But here in the Cambrian, in the period when the Tapeats Sea covered this part of the world and then built up this sandstone, that period was when diversity got going in a big way."

"Can anyone tell me how many different branches of the evolutionary tree got started then, out of those Supercells?", asked Alan munching an Oreo cookie offered him by Marsha.

"Aren't there something like 28 phyla of animals? Hundreds of orders, millions of species? Plus the protozoa and the plants?" volunteered Jackie.

"What's an order?", asked Jim.

"The primates are an order," answered Jackie. "We're in the phylum called chordates, along with some invertebrates like the tunicates, which we probably evolved from. Vertebrates are a subphylum of chordates; mammals are a subdivision of vertebrates, called a class. The orders are subdivisions of the classes, such as the primates among the mammals. It's subdivided further, of course; we're part of the Old World monkeys, then the apes, then the hominids along with Lucy, then the genus Homo and the species sapiens."

"Don't think that I brought enough gold stars for this group," Alan resumed. "Well, the last time we shared a common ancestor with a lobster or an octopus or a mosquito was clear back here just before the Cambrian, like 600-million years ago. There were sure a lot of different blueprints for success started back then."

We all looked ahead at the 10 paces remaining of the hundred. "Well, let's go two paces, up to 400-million years ago. That's when animals started colonizing the land, plants got a head start on them half a step back. And in the sea there are proper fishes with hinged jaws. We're up in the bottom of that Redwall now, amphibians crawling in and out of the water," Alan said with a wave across the river at the canyon wall. "And then come reptiles," he said, taking another few steps, "and here we are at the end of the Permian, 248-million years ago. What happened then?"

"The Permian extinction," said Jackie, "when 75 percent of the sea-going invertebrate species got wiped out. That's also not long before the super-continent of Panagea broke up. But maybe a meteor helped things along too."

"Poor old Panagea," said Alan, holding his baseball cap over his heart. "Shattered. But," he said as he fitted his baseball cap back on, "you all know that ten continents are better than one for evolution to go its separate ways in isolation, so I suppose the breakup was a good thing. Too bad about those 75 percent of marine invertebrate species that died off during the breakup. I mean, there were some fancy animals that went down the tube then, like those trilobites you like so much. But, up with the dinosaurs. And, another step later, here at 200-million years, the birds split off from the dinosaurs. What somebody called a free bonus for excellence in thermal insulation."

Four steps remained. "You realize, of course, that the top of the Grand Canyon stops at about 245-million years ago. That fiend Erosion destroyed the evidence. Back about that time, the mammals and the placental animals went their own ways as they improved on matters reptilian. And then the mammals split up into all those orders, like rodents and carnivores and primates in these next few steps. But let's just step over all that and land up here at 65-million years ago." Alan plunged a stick into the sand and swirled it around. "Disaster strikes."

"The Cretaceous extinction. Goodbye dinosaurs," offered Brian, "as well as 50 percent of all the marine invertebrate species around at the time."

"Not to mention nearly all the zooplankton," Jackie observed. "That must have been some black cloud hanging over the Earth, to stop photosynthesis to the point that nearly all the little ocean animals starved. I mean, since those phytoplankton produce 90 percent of the oxygen consumed by us animals, isn't that calling it a little close?"

"There are lots of plant and animal species that didn't make it through those terrible times," observed Barbara. "But that created some empty niches, and afterwards the primates expanded to fill some of them. What were mostly little tree-shrew sorts of animals, not unlike rodents in many ways, suddenly evolved into monkeys. And somewhere about this next-to-last step, they split up into New World monkeys and Old World monkeys, getting separate continents on which to go their own ways. South America and Africa."

"Thank you. And now, for my final step," announced Alan in a voice suggesting a roll of the drums, "we shall leap from monkeys to ape to man!"

"I've got to see this," said Rosalie. "For 99 steps you've fiddled around, and now for the last step you're finally getting down to serious business. The monkey business."

"You didn't like the nautiloids?", asked Alan in a hurt voice, "or my birds? I mean, I thought that the birds were a great invention, even if they were kind of accidental."

"You've got to look at the big picture, Rosalie," volunteered Cam. "Haldane once observed that the Lord must have been inordinately fond of beetles because He made so many different types. Something like 90 percent of all animal species are beetles."

"Oh, never mind," said Marsha. "I want to see this flying leap across the monkey gap."

Alan braced to leap, but then fell abruptly down on his hands and knees and started walking his fingers across the sand while everyone laughed. "I think we'll have to reduce the step size a little, so we go 1 million years at a time rather than 50. Now about a third of the way along," Alan walked his fingers along to 34-million years, "the apes split off from the Old World Monkeys. That deserves a small stick." Alan planted the twig he'd kept behind his ear. "So it took half the time since the Cretaceous extinction just for the apes to get started. Maybe we'll just keep dividing the remaining distance by half, just like in Zeno's Paradox."

"Now the apes lived in the trees and, unlike the monks, they developed some real anatomical specializations for genuine hanging-by-your-hands brachiation. We've got their brachiator's shoulder joints, and monkeys don't. Now Marsha," Alan said, "just take your right hand, reach around behind your head, and scratch your left ear."

She did it with a flourish. "Some women put on ear-rings this way."

"Did you know that a monkey couldn't do that? Their shoulders just don't have that many degrees of freedom. This business of apes being more clever -- that might not have been the main thing when they initially diverged. Probably more like making a more efficient cherry-picker. You know, those trucks with little platforms that get positioned by hydraulics. Well, monkeys have to walk along branches like a squirrel, most of them. Now an ape can swing along under a branch, hanging on with one hand while picking fruit with the other hand. Sure, they can swing from tree to tree too, but that's nothing special. Just think of those flying squirrels that glide between trees with the greatest of ease."

Alan took another 17 finger steps, arriving at 17-million years ago. "Now in half the remaining time, the apes make it all the way to an extinct ape called Ramapithecus, or Sivapithecus -- whatever, you can remember him easily by thinking of your favorite orangutan in the zoo. Now the orang is a pretty smart animal -- somebody demonstrated to one how to flake a rock, took the sharp flake, and sawed through the rope that tied shut a box of goodies, and then went away to watch what the orang would do with a new set of materials and a new sealed box of bananas. Sure enough, the orang made the tool and then used it to get into the tied-up box of bananas."

"It's a pity they're not more social animals," observed Barbara. "The adults are loners, getting together only occasionally for mating purposes because their food is spread out so thinly that each requires a large territory. They're certainly clever enough that, with the boost provided by social life and observing the inventions of others, they might be more like chimps. At least as juveniles, they're certainly clever and social enough. Their adult lifestyle is what limits them, I think. Evolution is full of dead ends. That could have been us."

Alan was not to be deterred from his timetable. "Half again, and down here -- let the fingers do the walking -- we indeed get to chimps and gorillas. That is to say, we last shared a common ancestor with gorillas about 10 or 11 million years ago, with chimps maybe 7 or 8 million years ago. They keep changing those numbers on me every year, so I might be a little out of date. Since chimps and gorillas might also have changed some since then, you have to make allowances. But here at maybe 7 million years ago, you've got the last split in the hominid lineage for which there are several descendants still living today -- though the apes may not be long for this world if the human population keeps growing and cutting down their forests. There were various splits since then, in this here hominid line, but all the side branches have died out -- excepting us, of course. And we're working at that too."

"Now," observed Alan, "we've only got another eight little finger steps to go. And 8 million years ago, East Africa was getting pushed higher and higher by lava welling up, making a big blister in Kenya and Ethiopia -- just like this here Colorado Plateau was rising up about the same time, creating this canyon we're in. Not only does elevation change the local climate, but the whole world was getting a whole lot drier back in the late Miocene -- forests were changing into grasslands and all that. And those fancy apes had to either retreat with the forests into refuges like where the gorillas live now, or they had to get used to finding food out in the open country. Where there were lots of competitors. Even predators who liked succulent leg of ape. Dangerous place, there, out in the open."

"Well, somehow they managed, though there aren't many fossils from this period to show the gradual changes. All we know is that by 4 million years ago -- halve the remaining time again -- we've got old Australopithecus afarensis. Walking upright, almost as good as Jimmy. 'Course, they've still got ape-sized brains. Pint-sized brains, to be exact. Half a liter for you metric types.

Jimmy was hefting a softball-sized rock, an eyebrow cocked as he awaited Alan's next sentence.

"I didn't say it, honest," said Alan innocently. "Now some people I know may have pint-sized brains, but not Jimmy, no sir. You've all heard of ten-gallon hats? They were invented for our Jimmy."

Alan quickly resumed his march before Jimmy could reply. "So, halve it again, and we're at 2 million years. Something funny has started to go wrong with the earth's climate in the middle of that last little step, sort of hot and cold alternating ten times every million years. And surprise, the brain size has started to increase. Furthermore, stone tools start to be found all over the place, as Barbara showed you. And there are soon three hominid lines going at once in East Africa. One was a massively built fellow who died out. Old Zinj baby, who increased his tooth size rather than his brain."

"And in another step, at 1 million years, there is only one species left going, our ancestor Homo erectus, with a quart -- pardon me, a liter-sized brain. Erectus has got the wanderlust, and by now he's spread out of Africa and is all over Southeast Asia, maybe even into Europe. But, just a tiny little bit further -- we've only got one finger step left before we arrive at today if Zeno's Paradox doesn't rise up to smite us -- the Ice Ages start in a big way. And the brain gets even bigger -- all the way up to three pints in Neanderthal, here in the thickness of the twig that marks today. But he died out too. Now in the thickness of the bark on that twig -- actually no more than a hair's breadth -- we arrive at the civilizations of the last 5,000 years, and science."

"Now in the last few years, less than a layer of dust on my finger-nail, science has discovered much of what happened during all that time" -- and here Alan swept his arm to indicate the length of the beach -- "plus these estimates of when it happened. There's even knowledge of how it occurred -- all that evolutionary bootstrapping."

Silence. "How about the 'Why'," someone asked. "You've covered 'What', and 'When', and a little bit of 'How'. But why did it all occur?"

I volunteered an answer. "The usual scientific prejudice is that if one figures out the 'How', the 'Why' will take care of itself. Not that the previous guesses about 'Why' have worked out very well. But making some guesses about how it all fits together -- which is perhaps our closest approach to giving an answer about 'Why' -- that's a part of science too. The only trouble is that it's always a temporary summary, soon out of date. But we keep on making models for how and why it fits together, even though they'll be superceded shortly."

"So why do you think it occurred?" I was not to get off lightly.

"Well, one way of looking at it comes from the new thermodynamics. That says there is a self-organizing tendency whenever energy is running downhill in a system, just like spiral eddies form downhill of rapids. There are a lot of levels of self-organization, evidently, and we just keep encountering one emergent principle after another, getting surprised by bird flight as an offshoot of keeping warm with feathers, getting surprised by consciousness as a free gift of enough complexity in a brain specialized for handling symbols and sequences."

If there is anything else, we'll never know except by wading through the long, hard process of eliminating the trivial explanations. If, indeed, one can use the word 'trivial' for such a piece of magnificent creation. It's only the individual pieces that are workaday machines and processes. Yet the whole is much more than the sum of its parts, and this whole has still escaped the comprehension of our limited brains. Our brains are much better at comprehending the pieces, and so we are much better at dissecting things than at visualizing the whole -- even when we know the individual pieces. It's only through clever metaphors, such as Alan's walk through time, that we can even attempt to comprehend the whole thing.

Numbers do not seem to work well with regard to deep time. Any number above a couple of thousand years -- fifty thousand, fifty million -- will with nearly equal effect awe the imagination to the point of paralysis.
...... JOHN McPHEE, 1981

Part of the resistance to Darwin and Wallace derives from our difficulty in imagining the passage of millennia, much less the aeons. What does seventy million years mean to beings who live only one-millionth as long? We are like butterflies who flutter for a day and think it is forever.
...... CARL SAGAN, 1980

AFTERWARDS, Dan Hartline and I walked down the beach again talking about brains some more. We stood at about 700-million years, just back of Alan's Cambrian stick.

The way I figure it, nerve cells must have gotten started sometime back about that time. Before that, individual cells did a little bit of everything -- they sensed the environment, they contracted to move away from trouble or toward food, they digested food. Paramecium are probably a good present-day stand-in for those pre-Cambrian cells. They have specialized channels through their membranes -- little gates that admit calcium ions, or maybe potassium or sodium ions on other occasions. It's the calcium entry that starts them swimming, beating their little hairs like so many Volga boatmen, to go zooming off in a new direction.

Dan suggested that sodium channels for sending electrical signals long distances must have been around before the time of the Cambrian, because even primitive nervous systems like the nerve net of a jellyfish use sodium to produce the nerve impulse, which is how an elongated nerve cell (some can be over 2 meters long -- they are, of course, very thin) tells its far end what's happening elsewhere. The signaling codes are very similar. Dan and I once did some experiments together on lobsters, and their multiplexing scheme (how nerves, and the long-distance telephone companies, send two independent signals down the same line) was the same as I'd earlier studied in cats, monkeys, and humans. One has to go back more than 600-million years ago to find a common ancestor.

Standing at 500-million years ago, when all the major phyla were underway, we compared notes and decided that the major types of circuits of nerve cells had probably already been invented by then. It does make one wonder, when the sensitivity-adjusting mechanisms for sensing muscle length turn out to be the same in lobster neurons as in humans. These involve two different chains of cells, interdigitating in just the right way, so that the sensory nerve ending is kept under the right tension to sense any new changes in muscle length. So perhaps lobsters and humans inherited them from a common ancestor.

Either that or a lot of groups later invented the same thing on their own. That does, of course, occasionally happen: the camera-type eye was invented by the mollusks in time for the octopus to use it, although it was invented independently in the chordate line for the mudpuppies and the fish. And, of course, us. That it was independent invention is known due to differences in the embryology of the eye between chordates and mollusks. In the octopus, the photoreceptors sensibly point toward the incoming light; in our eyes, they point away. Indeed, the light must pass through three or four layers of nerve cells in our retina before reaching the photoreceptors. This is terribly inefficient, since those nerve cells are not entirely transparent -- their DNA in particular is very good at scattering photons every which way, diffusing the image somewhat.

Now if the Creator had planned ahead properly, she would have done us the same way as the octopus. Instead, it seems likely that the pointing-the-wrong-way arrangement was an evolutionary patchwork job, which was sufficient for primitive chordates like mudpuppies, who live in murky river bottoms without much need for precision vision. And so the primates inherited the same arrangement. When monkeys needed better resolution for spotting fruit in trees, evolution just improved other parts of the visual system rather than starting over from scratch. As in other bureaucracies, one has to live with the shortcuts that predecessors took, procedures that have become so embedded in the system that redesigning them now is out of the question. The treasure hunt of chordate development just doesn't know how to build an eye any other way.

More recently than 500-million years ago, we're hard-pressed to put a date on an invention. We just don't know enough yet about the super-circuits (like those ones in the brain that tune up to detect hawks) to know if the birds invented them, or the vertebrates, or if they too were invented clear back here before things diverged into the many phyla.

Still, the major circuits for repeated movements -- the ones we use to walk and chew and swim and tap out a rhythm -- are all similar to one another. And they differ little between lobsters and humans. Again, that may be repeated invention; just like the eye's optics, there may be only so many really good ways of making a circuit oscillate. But it does make one wonder if the evolution of nerve circuits also hadn't been going on for hundreds of millions of years before things started fossilizing in a big way during the Cambrian. So a lot more may have been happening in that span between 1,300- and 600-million years ago than just the beginnings of multicellular animals. The foundations of our brains may be back in that Precambrian ocean.

Back to the boats.

The Powell expeditions through Grand Canyon [showed] that man had inhabited that seemingly inhospitable region centuries earlier. It should have been clear to the emaciated and battered explorers that those prehistoric aborigines were in many ways much better adapted to the environment than the explorers with their rancid bacon, soggy coffee, and mildewed flour. Indeed, the more intensive recent archeological studies [of Grand Canyon] have demonstrated not only that its depths provided adequate subsistence for a people technologically attuned to their habitat, but that movement on foot through its vast recesses was entirely feasible.
......the anthropologist ROBERT C. EULER, 1969

Mile 134
Tapeats Creek
Eighth Campsite

WE'RE MAKING CAMP EARLY this afternoon so that we can hike up to Thunder River. Thunder River is surely one of the few rivers that empties into a creek, which then empties into a river. So much for orderly names. We're anxious to see Thunder Spring, which gives rise to this short "river." The spring is one of the largest in the Grand Canyon. Certainly Tapeats Creek as it flows into the Colorado is the biggest stream we've seen since the Little Colorado, though it gathers its waters from a dozen springs up the drainage.

Tapeats has a large campsite spread out along the right bank, and it even extends along Tapeats Creek, going back in a ways. Tamarisk grow all along the shoreline of the creek, providing havens from the afternoon sun. Tapeats Canyon starts off easy, but then quickly narrows into a "box" canyon filled with a jumble of really big boulders through which the stream cascades. In some places, the stream fills the canyon from wall to wall, and one has to wade back and forth to pick through the shallow spots. Early in the summer, the water can be so high (and cold) that it is impassible. The walls are Tapeats Sandstone. Though we first encountered this corrugated-appearing khaki sandstone at the Little Colorado River, and explored it again at Elves Chasm and Blacktail Canyon, this canyon is the "type locality" for which the Tapeats Sandstone was named. And handsome it is.

It requires some agile climbing to get up over a steep talus slope. But once up, the slope becomes gentle, the ledges and terraces extending back for many miles. The Tapeats of the box canyon is replaced with the overlying Bright Angel Shale, which is easily eroded down to a gentle gradient (this is the same stuff that forms the Tonto Platform, that almost flat region one sees looking down from the Canyon rims just before the V of the granite gorge finally goes down to the river -- it's such crumbly rock layers that give the Canyon its breadth).

On the tops of some of these terraces are Anasazi ruins, originally noted by the second Powell expedition in 1872. We explore one Pueblo-style ruin on the right side of the creek, which has four rooms flanking a series of storerooms. These ruins, alas, have been pot-hunted. But Subie says that the potsherds recovered have all been identified by Bob Euler as being from the period of A.D. 1100 to 1150, the same time as the final period of occupation at Unkar Delta. There are more than 2,000 sites like this in the Canyon, and most of them are from the one century between 1050 and 1150.

There is another one-room pueblo ruin on the other side of the creek, a good fifteen stories above the streambed, hidden behind a boulder that forms one of the walls of the room. Someone observes that one of the families must have sure liked their privacy. But of course it could be where the survivors of the lower pueblo moved after some disaster. Tapeats Canyon can be reached from the North Rim (even horses can make it down these days), and they might have had hungry visitors coming in along the same route after the drought set in about A.D. 1130. Thanks to Thunder Spring, this place probably had water long after others had dried up.

Somewhat further upstream, Thunder River comes down from the left; it is obviously contributing most of the water we see arriving down at our campsite on the Colorado. Hiking up Thunder River's short V-shaped valley via a series of switchbacks, we soon see where all the water comes from: it bursts out of the cliff through two openings, falls eight stories, and then foams and cascades another half mile down to join the rest of Tapeats Creek. This is surely the shortest river in the world. Up there to the right of the falls is a cave which leads back into the underground river, shortly before its emergence.

Thunder River from Leonard Thurman's Grand Canyon River Running web pages.

Continuing up to the left of the falls, we reach a crest, and a valley opens out below us. Surprise Valley. Abruptly, the sound of Thunder River is lost. Intrigued, some people hike back to the point where the sound starts and the falls come into view, a most dramatic entrance for anyone hiking the trail in the opposite direction. Out of Surprise Valley and into Thunder River.

Surprise Valley has a most unusual shape, rather like a bowl. Though a creek has been cut down from the Redwall in several places, it is hard to see where the water leaves the bowl. A topographic map proves illuminating: Bonita Creek takes a few sharp turns, again most uncharacteristic of the valleys around here.

Subie tells us that Surprise Valley was formed by a great landslide. All of the left wall of the bowl has slipped toward the Colorado River. About four square miles of rock slid sideways and temporarily plugged up the river; geologically speaking, it wasn't even that long ago that it happened.

"And what caused this great prehistoric landslide?", Rosalie asked.

"Probably water," answered Subie, "lubricating the slippery shale of the Bright Angel Formation. Thunder River indicates that there is a lot of river draining down off the high Kaibab Plateau of the North Rim. Maybe there was enough in the past to grease the skids."

"Or maybe the Colorado River was backed up," she added, "by the lava flow which once dammed up the river further downstream near Lava Falls at Mile 179. If this area was soaked by the backup, that might have lubricated things so that when the dam broke and the lake drained, the loosened block went sliding -- and created Surprise Valley."

One of the great landslides of prehistory. I cannot resist telling the others about the greatest landslide of historic times. It happened in 1980, when the top of Mount St. Helens slid off and uncapped the volcano. The volcano had been getting restless, and a spotter plane happened to be flying overhead when it happened. A series of earthquakes occurred right underneath the mountain, and the observers reported seeing the seemingly solid mountain begin to quiver like a bowl full of jelly. The top of the mountain then slid sideways and created the great landslide. It crashed down one vertical mile before reaching Spirit Lake. When it hit the lake, it caused a great wave of water to splash out of the opposite side of the lake. The wave washed up the mountain ridge behind the lake.

One can still see where the wave washed away the soil, because for a few years nothing grew on that whole end of the mountain ridge. It isn't just that the trees are missing -- they're blown down and stripped clean of branches and bark everywhere in that direction because of the great volcanic blast that followed the uncapping of the pressure cooker. The soil itself is missing, and so no new bushes or seedlings grow back. One whole mountainside, washed clean of soil down to the underlying rock by one gigantic wave splashed out of Spirit Lake. The ecologists have been studying how soils get started again in such denuded areas, as well as in the lifeless lava beds near the volcano.

SOIL ISN'T JUST THE SURFACE OF THE EARTH, as I thought when I grew up in the farm states of the midwestern United States. Rocks, which are mostly what one walks on in this desert, aren't soil. Soil is a living ecosystem; it can be killed, for example, by heat from lava flows. Soil is partly formed of things which are living or were once living and are now decaying; these organic (carbon) materials are mixed in with inorganic "minerals" such as potassium and nitrates. The organic and inorganic molecules that are useful to living cells are called nutrients. Soil also contains water and air spaces; the mix of particle sizes is very important, since sand alone won't hold water, and clay alone won't let in water. Bacteria in the soil do all sorts of useful jobs, such as fix nitrogen in the soil so that plant roots have nitrate fertilizers; the plant that extends a stalk up above the soil is only the tip of a mountain of subterranean goings-on.

In Tapeats Canyon as we hike back, Alan points out how soil gets started. Here and there among the sand and rocks are some dark patches of crusty stuff; often some plants grow adjacent to them. The dark material sometimes covers the ground like a lumpy black crust, looking almost like a skin disease. The dirty stuff is cryptogamic soil, the simplest of the soil ecosystems. Cryptogam means "hidden marriage," and tells of the cooperative relationship between bacteria and the simplest plants. Soil starts simple and co-evolves with the plant life. Knowledgeable desert hikers avoid stepping on the cryptogams; these primitive living systems have a hard enough time without disruptions, and a careless footprint can set them back decades.

The buildup of a soil can be aided by things blowing in from the outside; the new lava beds near Mount St. Helens are starting to build up new soil in nooks and crannies, just because that's where blowing things are trapped. Dead insects, for example, blown up from lower altitudes may lodge there and contribute their decaying organic compounds to the new soil. But cryptogams show how soil can get started without so much outside help from decaying higher life forms; their blue-green algae (now classed with the bacteria rather than the other alga) use sunlight to convert atmospheric nitrogen into a waste product containing nitrates, which serve as food for fungi (which cannot do their own photosynthesis). This symbiotic combination, called a lichen, also helps retain water and thus provides a home for mosses, another component of cryptogams.

Plant life has to build up through a slow succession of ever more complex types; each decade or century sees a new type of bush or tree dominate. The speed of the succession depends on the weather and the soil. For example, the Anasazi's corn needs the right amounts of potassium and nitrogen in the soil. Their beans could get along in soil that was low in nitrogen, so long as they had enough water. And once soil has had beans (or other legumes such as clover or alfalfa) grown in it for a while, the soil accumulates enough nitrogen to grow corn, thanks to the bacteria in the legume roots which fix nitrogen; while plants use most of the atmospheric nitrogen they convert to ammonium compounds, the bacteria convert so much that the excess is excreted as nitrates into the soil. Natural fertilizer.

I don't know if the Anasazi knew about this crop-succession principle; perhaps they just found the better soils for corn by trial and error. But the Indians didn't domesticate corn without many generations of selecting the right plants and soil (and corn is one of their major contributions to our civilization). So it wouldn't surprise us if they knew about crop rotation too.

Many European farmers have found out the hard way that the methods of their ancestors do not work in parts of the wet tropics. If you clear a typical piece of red tropical land, plough it up, and sow seed, your efforts are poorly rewarded. There may be a few years of struggle against falling yields, but then comes the bitterness of defeat, and a patch of red mud is left for the wild weeds.... How have the forest trees [of the great tropical rain forests] managed to thrive in a soil washed clean of nutrients?
.......the ecologist PAUL COLINVAUX, Why Big Fierce Animals Are Rare, 1978
THE RED SOILS OF THE TROPICS remind one of all the red rock and sand around here, but they're poor soils for a different reason. In the temperate zones, the good land has a very different soil than in the tropics. With proper crop rotation (such as planting legumes every few years to build the soil's nitrogen back up), good soils -- if they're not ruined by salt from irrigation -- will grow all sorts of things for a long time. But in the tropics, the soil has been so regularly washed by the rains that many of the soil minerals have been washed out to sea. The nutrients in the forest floor would wash out to sea too if it weren't for the fine network of plant roots that trap them as they wash down. All of the dead animals, the insect excrement, the decaying plant materials -- they're all neatly trapped by the super-efficient network of living tree roots, with the help of special types of fungi that live on the roots. Cut down the trees and the roots die. What isn't burnt washes out to sea. And the remaining soil has little to give a new crop.

And so you can't simply plant a tropical rain forest, even if you had all the right seeds to sow. Even if a rain forest grew in the same region some years earlier, starter plants can't take hold, because of the lack of the right conditions (such as shade!); it might take millennia of slowly evolving soils and successions of plant life before a rain forest complex could ever exist again. Once a rain forest is cut down, the building materials are lost and the necessary shade is lost. It's not like a European or North American forest that might return in a century or two.

The web of roots in the rain forest reminds me of the mammalian kidney, that super organ that dumps the liquid part of the bloodstream into the plumbing that leads down to the bladder, but then -- before the fluid actually reaches the ureter and is declared waste -- neatly grabs back those molecules that it wants to save, thus keeping the right proportions of salts in the body.

The lush tropical forest, then, is a great accomplishment of slow evolution, but one that cannot be repeated on order, simply by reseeding a clear-cut. Once they're gone -- and they're being cleared at a ferocious rate due to the Third World population explosion -- the rain forests won't be back for a very long time. And the animals that live there will all be dead. The species that lived only in those forests won't ever be back: extinction is a very permanent fate. A large fraction -- more than half -- of the world's animal and plant species will become extinct within decades if the clear-cutting of the tropical forests continues.

Except in cases like that of Brazil, where the Amazon is often cleared simply to grow grass for cattle which will be exported to the rest of the world as cheap beef for the fast-food industry, it's hard to blame the people who do the clearing -- they're us, just a little less educated and a little more hungry. The problem is the inflationary times in which we've lived since agriculture got started about 10,000 years ago: just as prices tend to rise in times of prosperity, so population numbers tend to rise as couples raise as many children as the local resources can bear in the short run. In the long run, a lot of people and animals are going to starve unless the renewable resources (which a tropical forest isn't, except at low human population densities) are brought into balance with the population.

Scientists aren't very popular when they come bearing such bad news, and one doesn't find newspaper headlines in Third World countries concerning what they've got in store for themselves only decades ahead if they keep expanding the population and clearing the forests. It's not quite like eating the seed corn, but it comes close.

Tropical forests are being besieged by armies of subsistence farmers who cannot survive in cities.... Each year humans destroy enough tropical forest to blanket all of England. Among the several dire implications of this devastation is that a mass extinction of tropical species appears imminent. And, since tropical forests are the homes of between two and four million of the estimated five to ten million species on the face of the earth, it could well rank with history's several great mass extinctions.
.......the biologist DANIEL SIMBERLOFF, 1985

... if no country pulls the [nuclear] trigger the worst thing that will probably happen -- in fact is already well underway-- is not energy depletion, economic collapse, conventional war, or even the expansion of totalitarian governments. As tragic as these catastrophes would be for us, they can be repaired within a few generations. The one process now going on that will take millions of years to correct is the loss of genetic and species diversity by the destruction of natural habitats. This is the folly our descendants are least likely to forgive us.
......the biologist E. O. WILSON, 1984

THE SUNSET WAS UNUSUALLY RED TONIGHT, long before dinner was finished. Many thought it pretty, but some of us who live in timber country had mixed feelings. It was the kind of red that one sees when a forest fire has settled a pall of smoke over the western sky. Pretty, but discomforting at the same time.

Smoke sometimes spreads for long distances. In 1950, forest fires in Canada made the sunsets similarly red in Europe; they created a haze that cut the daytime sunlight in half in Washington, D.C. During a heavy overcast, only about 10 percent of the usual amount of sunlight reaches the surface of the earth. And volcanic eruptions have been known to reduce it even further: the towns downwind from the Mount St. Helens eruption in 1980 had their automatic streetlights lit at noon.

"That sounds like what happened to Moses," commented Jackie. "The people in Egypt couldn't see one another or move around for three full days."

"Another one of those pesky Mediterranean volcanos," Ben replied. "Suppose it was Santorini, popping off?"

Just as an overcast sky means a cooler day, so smoke or ash clouds also cool the earth's surface. Benjamin Franklin, as usual, had something to say on the subject: he suggested that the 1783 Laki eruption in Iceland was the cause of Europe's cool weather and poor crops. There is now evidence from the tree-rings of very old trees, such as the bristlecone pines in the mountains of the western United States, that early frosts occurred in the years of major volcanic eruptions elsewhere in the world. Thanks to the accuracy of tree ring counts, 1626 B.C. is now estimated to be the year of one of the greatest volcanic eruptions of historic times, the Santorini (Thera) eruption in the Aegean Sea. The climatic effects of such an eruption can be major: following Tambora's eruption in Indonesia, 1815 was called the "year without a summer" in faraway Europe.

Scientists had been studying the effects of dust injected into the atmosphere by volcanos ("a stratospheric veil of fine silicate ash and sulphur aerosols, with resultant surface cooling"), stimulated not only by the marked climate changes that have followed some eruptions but also by the results of one of the unmanned spacecraft which flew past Mars in 1971. There it found a giant dust storm which enveloped much of the planet and took 10 months to clear. Could that happen here? Why does dust take so long to settle out of the atmosphere? One answer is that, if it gets up high enough, rain won't wash it out anymore.

And how does dust get up that high? When the geologist Walter Alvarez discovered unusually high concentrations of the rare element iridium in 65-million-year-old layers of rock in both Italy and Denmark, he considered whether the breakup of a meteor might have caused it. He, his father the physicist Luis Alvarez, and others postulated in 1980 that such a meteor could have kicked up enough dust to cause the Cretaceous extinction, that wiped out the dinosaurs and so many other species about that time. The giant dust cloud they postulated got everyone to thinking about extinctions and atmospheric disruptions.

But what about smoke? It was a new consideration to many scientists, despite the smoky sunsets of 1950 and other years. In 1977, George Woodwell of the Woods Hole biological labs suggested that all of the clearing of tropical forests that was going on might, because of the burning, be injecting more carbon compounds into the atmosphere than all the coal and oil burned in the Northern Hemisphere.

Smoke can also get high enough in the troposphere to avoid being washed out immediately; when it does wash out, it causes acid rain, as the people and wildlife downwind of industrial centers well know by now. Smoke at any altitude is far worse than dust -- one big difference is that, while dust tends to reflect light back into space that would have otherwise reached the earth's surface, the black carbon particles tend to absorb light and heat up, thus heating the air molecules around them much more than dust does. Heating up the middle atmosphere, while simultaneously reducing the heating of the lower layers near the earth's surface, is just the sort of thing to give nightmares to atmospheric scientists: the circulation patterns that carry weather around are quite dependent on the temperature gradient between the lower and upper atmosphere.

El Niño, the Pacific Ocean climate change which seems to occur every half-dozen years or so, causes a lot of fishermen's families to go hungry (air temperatures affect ocean surface temperatures and thus ocean currents, such as the upwelling off Ecuador and Peru which carries nutrients to the surface and feeds lots of fish). El Niño's mysterious rearrangement of Pacific weather patterns seems to be associated with a change in the temperature gradient between the lower and upper atmosphere. It is clear that volcanos can make El Niño advance its schedule, causing it to arrive much earlier than normal -- probably by modifying the atmospheric temperature gradient by injecting ash into the middle and upper atmosphere.

Injecting a lot of smoke into the atmosphere might be even more serious because black soot particles in the smoke upset the usual vertical temperature gradient even more than light-colored dust. Volcanos and other natural causes are bad enough when humans are living close to the edge of their food resources: burning a lot of vegetation in the tropics is a serious matter for people living anywhere there's weather. But that may not be the worst of it.

The nuclear winter story actually started with supersonic jets and ozone, the three-atom oxygen molecule that tends to accumulate in the stratosphere and screen out much of the sun's ultraviolet light that would otherwise seriously damage plants, not to mention human skin and eyes. In Germany, Paul Crutzen's studies of the ozone layer called into question the building of supersonic passenger jets in 1971. He then contributed to the subsequent studies which had led to the concern over refrigerator coolants and the propellant gas used in spray cans, because of fluorocarbon's potential for destroying the ozone layer. In 1975, a U.S. National Academy of Science report concluded that all-out nuclear war might destroy enough of the ozone layer to expose the earth's surface to lethal doses of ultraviolet light -- lethal to plants as well as people. The president of the Academy, in releasing the report, offered his personal opinion. He chose to look on the report as "encouraging," characterizing it as suggesting that much of the planet could recover from a nuclear war. In the furor that followed, ecologists Paul Ehrlich, Anne Ehrlich and John Holdren challenged the report because it virtually ignored the "huge firestorms" that would follow a nuclear attack. Woodwell made his calculations about Amazon burning. By the late seventies, Crutzen was studying burning trees in Brazil and trying to figure out what happened to the constituents of the smoke and vapors, worried that they too might affect the earth's ozone.

All of this formed the background to one of those startling serendipities that sometimes occurs in basic science, when one problem suddenly illuminates another. Smoke had some effects on ozone, but what might they do to temperature? Smoke hadn't been taken seriously before, and atmospheric scientists began to reevaluate the old studies about the aftermath of a nuclear war. Never mind for a moment all those people killed by the blasts and firestorms and fallout -- what sort of world would the survivors face? If volcanos can cause so much trouble, what would happen after all those bombs kicked up a lot of dust? And all those firestorms burned up all those cities with their fuel dumps and asphalt pavements and flammable buildings, sending smoke up high?

Crutzen didn't have data on burning cities, but he did have data on forest fires and he assumed that the city firestorms might spread to the forests. So Crutzen and an American colleague, John Birks, wrote a paper in 1982 for the Swedish environmental journal Ambio on the smoke from forest fires that a war might cause -- and calculated that a typical nuclear war might cause enough atmospheric disruption from forest fires alone to prevent 99 percent of the sunlight from reaching the surface of the earth, and that the effect might last for weeks.

As is obvious from the fact that temperatures drop during the night anywhere from 5-20°C. (9-36°F.), lack of rewarming during the next several days could cause the earth's surface to freeze in short order. As Paul Crutzen said when contemplating the consequences, "I don't think they know what winter is in India." Plants in the tropics have not evolved any protection against frosts; even high-latitude trees which will survive prolonged winter freezes can be killed by a quick frost during their summer season. Even a few days of dense overcast can have crippling effects on forests and agriculture.

Is a simple calculation reliable? One can't just experiment by burning cities down, but there is the smoke-haze data from forest fires. The volcanos and the weather records have provided a lot of data with which to calibrate computer models of dust in the atmosphere. But the next part of the story came when people working on very different problems applied their expertise to Crutzen and Birk's scenario. Carl Sagan and two of his former students, Owen Toon and James Pollack, had developed computerized models to study how the giant dust storm on Mars might have operated; Richard Turco and James Ackerman had been using a more sophisticated version of this computerized model to test the notion that dust clouds kicked up by a meteor striking the earth might have been the cause of the mass extinctions postulated by Alvarez et al. Turco saw an advance copy of Crutzen and Birk's work, and realized that smoke was much more important than dust because of what it did to atmospheric temperatures.

The five had gotten together to study the biologists' mass extinction problem, but now they shifted and extended Crutzen and Birks' calculations using the sophisticated computer "working model" of the atmosphere; they included estimates for burning cities as well as burning forests. Turco, Toon, Ackerman, Pollack, and Sagan wrote a paper (soon known by the acronym TTAPS) published in Science in late 1983 detailing the consequences of nuclear exchanges of various sizes and types; the TTAPS report was delayed one year, Sagan said, because their U.S. government sponsors were nervous about the political reaction and wanted more studies done before letting it become public knowledge. But news circulated quickly in the scientific community anyway.

Turco coined the term "nuclear winter" to summarize the consequences of the cold and the dark that would come from the smoke clouds of a nuclear war. It would get very cold -- Arctic winter temperatures -- and stay that way for months, much longer than Crutzen and Birks' first estimate. Indeed, between 4 and 9 months of subfreezing temperatures, depending on assumptions about the size and season of the war. In the interim year before the TTAPS publication, while the results were circulating privately, a group of physical scientists met to assess the Crutzen-Birks and TTAPS reports; every time they found a neglected factor that might lessen the effects, they also found several that would make things even worse. A group of biologists met to assess the longer-term consequences to the biology of the world. Sagan, the Ehrlichs, Woodwell, and fifteen other prominent scientists wrote a report that was published with the TTAPS paper; they evaluated the radiation doses, the ultraviolet effects, the bitterly acid rain, and the effects of the violent and frequent storms that would be generated by cooling land masses, and the disruptions to the ecosystems which the cold and dark would cause.

Because much damage could be done in the tropics by only a few days of slightly subfreezing weather, even the small-war scenarios looked dreadful. The biologists' report was understated, and had the language of compromise that nineteen different authors engenders, but it spelled catastrophe: "the possibility of the extinction of Homo sapiens cannot be excluded." A nuclear attack of any substantial size is, in effect, a Doomsday machine that would destroy the aggressors themselves within a month -- and, unfortunately, much of the rest of the earth as well.

It would wipe out the agricultural and industrial system that supports a world population far larger than in preagricultural or preindustrial times; the grain harvests that provide 70 percent of the world's dietary calories are surprisingly fragile, even threatened by drops of 2° to 5°C. in the average daily temperature. A full-fledged nuclear winter wouldn't merely reduce us to 0.1 percent of the world's present human population, the level that hunting and gathering supported before agriculture -- there might also be too little to hunt and gather for that remaining one person in a thousand. Even if it didn't wipe out humanity, the war would likely reduce the population to a tiny fraction of its present size, and destroy civilization as we know it through the actions of starving mobs.

It would undo the world painfully built up by our ancestors, whose suffering and failures shaped the survivors into the species we are today. The apes, who today live in precarious habitats unlikely to survive even the cutting of the tropical forests, would surely succumb. Some monkeys might survive in the Southern Hemisphere, but no scientist can be sure. It might be more than 50- to 100-million years before the gearwheels of evolution again created anything as fancy as our civilization -- or perhaps 500 million years, or never.

And we have ignored the possible effects of radiation. Someone once said that nuclear war could reduce life on earth to a radiation-resistant grasshopper eating a radiation-resistant grass.

The mechanism most likely to lead to the greatest consequences to humans from a nuclear war is not the blast wave, not the thermal pulse, not direct radiation, not even fallout; rather, it is mass starvation.
.......MARK HARWELL and THOMAS HUTCHINSON, Scientific Committee on Problems of the Environment, 1985 report.

John Holdren... commented that what amazed him was that [any national leader] who had seriously contemplated the acceptability of losses implied by direct blast and radiation effects (which could be as high as a billion people) could be considered rational, and would probably be unmotivated by the further recognition that perhaps four billion people could be threatened by the longer-term climatic effects.... We would be appalled to learn that any governmental official who continues to believe in a winnable large-scale nuclear war could remain in a position of responsibility in any sane nation on earth. Perhaps most disquieting of all is the fact that people with such warped values are both responsible for strategic planning and are at the same time protected from public censure by the legal cloak of secrecy.
......STEPHEN H. SCHNEIDER and RANDI LONDER, The Coevolution of Climate and Life, 1984.

BAD AS THIS IS FOR HUMANS nearly everywhere on earth, it might also rate with the mass extinctions as a killer of whole major groups of plants and animals.

Despite the "winter" aspect, nuclear winter is not to be confused with just another ice age; the great extinctions said to be caused by meteors are the more appropriate comparison, if indeed anything in the earth's history is similar. When the climate changes slowly over thousands of years, there is time for humans and other animals to move around, find new ways of making a living, time for ecosystems to adapt and most species to survive. When the change happens in a matter of days, the results are far different. It's the difference between the melting ice caps causing sea level to slowly rise over the millennia and an earthquake causing a giant tidal wave to violently denude a whole coastline in minutes. Except that with a nuclear winter, it isn't just coastlines.

We have called into question the Old Testament reassurance about the continuation of life:

One generation passeth away,
and another generation cometh:
but the earth abideth for ever.
.......ECCLESIASTES 1:4.

Many more species have become extinct than are now alive.... We are unimportant in the history of our planet, which got along very well without us for several thousand million years. If we lose the flexibility to adapt, we too will become extinct. Other species will take our place, fill our niche, and carry on the evolutionary process -- unless we, in passing, so alter the conditions for life that no existing organic forms can survive.

You know, there's no reason to believe progress is inevitable. I'm a medieval historian and believe me, people are quite capable of mucking things up.

The Earth is just too small and fragile a basket for the human race to keep all its eggs in.

The systematic mass murder of European Jewry made it clear that entire civilizations of the highest cultural and scientific attainments could in the course of a few years go rabidly mad; and the invention of nuclear weapons insured that insane nations of the near future would command the means to destroy life on Earth.
...... MATT CARTMILL, 1983

We have become, by the power of a glorious evolutionary accident called intelligence, the stewards of life's continuity on earth. We did not ask for this role, but we cannot abjure it. We may not be suited to it, but here we are.
...... STEPHEN JAY GOULD, 1984

We no longer have the choices to make, or the options of a few months ago to argue over. We simply must pull up short, and soon, and rid the earth once and for all of those weapons that are not really weapons at all but instruments of pure malevolence.
...... LEWIS THOMAS, 1984

If it should turn out that we have mishandled our own lives as several civilizations before us have done, it seems a pity that we should involve the violet and the tree frog in our departure. To perpetrate this final act of malice seems somehow disproportionate, beyond endurance. It is like tampering with the secret purposes of the universe itself and involving not only man but life in the final holocaust -- an act of petulant, deliberate blasphemy.
...... LOREN EISELEY, 1963

Do not go gentle into that good night.
Rage, rage against the dying of the light.

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