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William H. Calvin
This page is at http://WilliamCalvin.com/bk3/bk3day12.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).

DAY 12

Mathematical relationships tend to show a forever-surprising basic simplicity, as if implying that certain, relatively few fundamental laws, or their variants, underlie the infinite multitude of the observable detail that offers itself to our senses. To discover that the universe is structured, and moves, according to mathematical laws is to experience one of the most profound insights into the basic order of the cosmos.
......the historian THOMAS GOLDSTEIN, Dawn of Modern Science, 1980

Mile 166
National Canyon

IT'S A LITTLE EARLY for clouds. We're washing up before breakfast, and it is already overcast. Monsoon-type clouds don't usually build until afternoon, as the heat rising from the Canyon pushes up the moist ocean air coming up from the Pacific and Gulf of California. So these clouds must instead be a weather system. Grumble. But monsoons are another emergent property to add to the list -- clouds emerge!

Perhaps we should add music to the emergent-properties list, as a sidestep from sequencing. And what was that other item from our first afternoon on the river? Ah, yes -- humor. Can we explain that as another sidestep from sequencing? It does seem all tied up with our scenario-making consciousness -- the surprise ending that plays on your expectations, and all that.

"But," asked Abby, who had originally posed that question, "what about laughter? I mean, it's almost involuntary, like a reflex. Why?"

We thought for a while as we were standing in the breakfast line. The best thing that we could suggest was that exhaling explosively might be related to the breathing control that we acquired for diving, perhaps in our aquatic phase. But why the link to mismatched expectations? We are stumped.

Maybe, suggested Ben, the outburst of laughter is related to literally "holding your breath" while awaiting the outcome of the joke!

AN UNEXPECTED SOCIAL CONSEQUENCE of the Law of Large Numbers surfaced after breakfast as we sat around avoiding the topic on everyone's minds, located downriver. This bit of sociology can be seen in the hiring of civil servants and, of particular concern to many of us, in the awarding of research grants. While our example is from the sociology of science, it's the same thing that happens in many committee decision-making processes, one with many implications for big corporations.

There is literally a priority list in most scientific fields: the funding agencies enforce the priorities seen by the established experts. Those scientific experts aren't narrow but the money available is thin. Of the applications their expert consultants select as worthy, the agencies can fund less than 20-30 percent (it used to be 50-65 percent). This inhibits re-checking the data collected by others ("That's been done before, so it's hardly top priority"), together with the pressure from animal protectionists and legislators who heap scorn upon "duplicated effort" as if basic scientists were defense contractors proposing to develop an existing airplane all over again from scratch.

But even more serious is that this top-of-the-pile-only funding unintentionally stifles diversity. Among the democratic ideals that we Americans hold up, hoping for the rest of the world to copy, are the virtues of diverse political viewpoints and diverse businesses that compete for the consumer's approval. To these ends, we promote freedom of speech, diverse ownership of the press and media, capitalism without monopoly, states' rights, and the rights of the minority to hold a different view without being squelched by the majority (this civil liberty is largely what the U.S. Constitution's First Amendment is all about). School textbook adoptions are made by hundreds of different boards; there is no single approved promulgation. We encourage investors and small businesses to take risks. To our children, we hold up as heroes those who proved the experts wrong, the inventors who persevered and won.

Despite these ideals, we have created and allow to persist a system that forces scientists toward a mainstream. Our scientific heroes of the past, who followed the questions which most appealed to them, who saw it as a duty to duplicate the important results of others, who were independent -- just like the medieval knights who went around doing good deeds, they too were usually men whose investments gave them the leisure and wherewithal to do things without first getting the approval of a committee and waiting several years after having the idea to start working on it. Most scientists today are paid less than garbage collectors. They often cannot afford to send their children to the universities from which they themselves graduated. In many cases, their tenure in their jobs lasts no longer than their current two- or three-year appointment or research grant. Completely dependent on the piecework grant system, they become cautious, careful not to antagonize others who might advise on whether their research grant will be renewed, aware from their friends' experiences that years of careful work can be "terminated" if their next renewal doesn't make it into the top 16 percent of worthy applications, scattering specially trained personnel to the winds while one tries again to find money. It's even worse than being the proprietor of a bankruptcy-prone small business, since there is no opportunity to recoup a funding loss in a good year.

The U.S. government channels money into basic research through mechanisms developed in the years just after World War II. They bear the stamp of a peculiar model of science fostered in legislators' minds by the Manhattan Project, in which physical scientists abandoned their academic surroundings to beat Hitler to the atomic bomb. It is an unrepresentative model for several reasons: it concerned physics and chemistry, not the full range of social, biological, and physical sciences. It was a technological rush job, not an investigation in basic science -- even though the actors were mostly mathematics, chemistry, and physics professors, they were temporarily practicing applied technology, not the questing for unknown principles that characterizes true basic science (since the thirties, physicists had known the principles through which massive explosive power was available in the atom's nucleus; the 1942-1945 Manhattan Project was a great engineering endeavor to produce a portable bomb). Part of its legacy is the notion that group science is better than individual science -- and that scientists be kept on a short financial leash.

The principles on which the U.S. National Science Foundation and the National Institutes of Health award research money seems (on the surface) more sensible than the one-person-decides principle on which the armed forces often award research funds (they are still an alternate source of money in some fields, if one can tolerate the potential censorship). Incredibly, though he or she may consult with advisors, a young military officer with a master's degree in engineering may make all funding decisions for wide areas of basic science. The civilian agencies make more use of "peer-review," literally a jury of one's scientific peers -- though usually biased in membership towards the established, more senior scientists (they are not picked by the scientific community but by a bureaucrat). The civilian agency's scheme seems more "democratic," but it has some surprising, unwanted consequences -- maybe the military has the better idea after all, many different pots, each tended by a different person every so often as officers rotate.

Rosalie said that she couldn't understand how twelve people -- who, as individuals, were bright, inventive, broadly educated, delightful scientists -- could, convened together into a peer-review committee, turn into twelve conservative scientists with limited horizons. What did the committee do to them, make them all into social conformists, so that they selected only "mainstream" people, and rarely those who prefer to explore opportunities off the beaten track? Perhaps. But there's another more likely explanation, that the Law of Large Numbers has struck again.

Everyone tends to look upon a selection committee as rank-ordering the best, the runner-ups, the also-rans, and the unworthy. Yet it isn't a horse race --it's more like comparing apples and oranges. Quality enters in, but preference often overrides. Fewer than 10 percent (often none) of the committee members are likely to be expert enough in the subfield of a particular proposal to judge it on any basis other than "attractiveness." So what do they wind up selecting?

The answer is that in attempting to select "the best," a committee merely selects the most widely acceptable, the most attractive to the members' diverse tastes. What else can it do? The proposals selected may merely be in the middle of the diversity. The committee members may think that they are judging "quality" rather than consensus, but one person's expert quality rating is often cancelled out by a less informed member's attraction to another part of the diversity spectrum. Even if the members are individually truly unbiased and quality-conscious and representative and enlightened, such a committee process can still result in the stifling of diversity -- when there is only enough money to fund a small fraction of the worthy applications.

Consider a diverse committee able to hire only two of a diverse group of applicants (imagine, perhaps, a city council hiring civil servants). Because consensus may be hard to reach on the others, only the applicants acceptable to a majority will be hired (they may be no one's first priority or highest quality estimate). The next time two jobs open up, the same thing happens again. Take note: the employees as a group will wind up being less diverse than the committee that hired them. Increasing the diversity of the committee membership won't necessarily change the diversity average, and so it's the middle-of-the-road which gets hired.

This isn't inevitable: there are some ways around this mainstreaming effect. If we have fifty jobs to fill at once rather than two, we will be guaranteed some diversity. If the committee members can trade votes, work out deals that result in alternation in hiring favorites, employee diversity might be somewhat broadened. Some committees may be particularly enlightened and strive to achieve some diversity -- but the Law of Large Numbers suggests that the typical committee is going to have a natural tendency to select applicants which, as a group, are less diverse in their interests than the committee itself is. It's a result completely contrary to the perceptions of the well-intentioned committee members, each of whom is sure that quality counts. But the whole is different than the sum of its parts, and a committee performance is not merely the sum of a dozen quality judgments when a spectrum of interests is also involved.

When the money is thin, and the selection committee is really more a one-time jury that is prohibited from bargaining about reciprocation next time around (which are indeed the rules in the peer review of science research), it hires the middle-of-the-road -- time after time after time. Now in science, the average in diversity may be high in quality -- and usually is, since there is nothing mediocre about 95 percent of the applications competing for funds.

The danger is that this system will breed much of the off-center diversity out of the scientific population, just as animal inbreeding eliminates useful-at-times traits in favor of one currently-popular trait. In wild populations of animals, there is usually a wide range of diversity in the gene pool; whatever the climate dishes up next in the way of problems and opportunities, there will be some members of the species that have approximately the right set of insulating hair or sweat glands, of grazing or hunting instincts, of few-at-a-time or mass production in matters reproductive, of early or late breeding seasons. And the species survives. The inbred species, who may be uniformly great at turning grain into meat, may perish when the climate changes.

In science, we don't know where the future lies, where the revolutionary results may crop up (who'd have predicted that studying what happened to the dinosaurs would illuminate an unrecognized doomsday machine?). Try as we can, we cannot even predict the technological marvels of ten years ahead, much less the scientific ones. Diversity makes a lot more sense for institution-centered basic science than does emphasizing an artificial judgment of "the best." Spreading your bets means backing occasional losers, having pseudoscience occasionally get money that would -- with hindsight -- have been better spent elsewhere. Rather than the Congressional obsession with "wasted money" and auditing researchers' hourly efforts (they somehow think that our life's work can be treated as piecework in a repair shop), we need an audit for risk-taking: is an agency funding enough failures? When a good hospital reviews a surgeon's track record, it looks for too many patients dying -- but also for not enough dying. It isn't always variations in surgical operating skills that cause the high or low mortalities: variations in judgment and risk-taking play an important, though less obvious, role. A surgeon with no failures is a surgeon who plays it so safe as not to operate on a patient "who will probably die anyway." Some of those patients can be saved, but only by a surgeon willing to risk a personal failure. Researchers need to be able to gamble on long shots -- but our present grant system penalizes that.

A committee with a small pie to divide up may be worse than no committee at all if the tight-money situation persists. If it is a sieve for the whole field, the fringes will be eliminated. Time after time after time. If we are to stand a chance of bailing ourselves out of the nuclear and ecological mess that our blind governments and juggernaut economies are creating, we are going to need both scientific depth and breadth to diagnose the problems, to propose cures and workarounds. We will indeed need to do what the Manhattan Project finally did: rather than trying to judge which manufacturing process was best for purifying the rare isotope of uranium, it tried all three known processes. At once. In parallel.

Of course we need more money. Research deserves its long overdue reinvestment of some of the profits already generated from the ideas and techniques that basic science has already donated to the marketplace (don't suppose that Hertz's family or university gets royalties for every radio manufactured, or Maxwell's, whose equations made it all possible). But we also need to protect the scientific minorities from the well-intentioned committee majorities. We cannot continue to filter all the money through one or two sieves in which only the middle-of-the-road proposals win. In a country that prides itself on protecting political minorities, it is hard to understand our drift in science toward center-take-all and winner-take-all.

BOREDOM IS VERY IMPORTANT in an evolutionary perspective, we've decided. What is the use of a tendency to get bored with your food? Well, it promotes diversity of diet, so that one seeks out foods with vitamins and trace minerals. Boredom thus helps prevent deficiency diseases. Boredom of taste tends to be expressed by the changing of habitual behaviors, thus trying a different food-gathering strategy for a while -- literally "doing something different."

Yet some animals achieve well-balanced diets with a monotonous food-gathering strategy: gorillas chewing their plants, dolphins catching their fish. The lack of boredom (those animals apparently don't need it to avoid deficiency diseases) may unfortunately spell an evolutionary dead-end for those species; since they're not stimulated to seek out infrequent foods using infrequent behaviors, they don't discover the virtues of new combinations of pre-existing behaviors. Therefore, boredom could be an important stimulus to evolution among the animals, particularly omnivores.

And when one begins thinking about thought processes, one realizes that boredom is a critical parameter. Not enough boredom and you'll stay stuck in a rut. Too much boredom and you'll be hyperactive, constantly jumping around, failing to develop expertise in any one area. If we ever build a "thinking machine" in any true sense of that overused phrase, we'll have to adjust its "boredom factor" carefully so that it achieves breadth in coverage and occasional depth.

Common sense isn't faring very well on this trip. We seem to be collecting a paradoxical set of virtues: randomness, cowards, noisy nerve cells, even boredom. What's next, Cam quips: illness? And so we reminded him of the pathogen-escape hypothesis for the origins of sex, and thus our great evolutionary diversity.

Today's common sense is yesterday's science.
......the physicist NEILS BOHR

AN INHERITED BRAIN DISORDER is a puzzle if you're a creationist, but more understandable -- though it doesn't exactly achieve the status of a virtue -- from an evolutionary viewpoint. It certainly shows that natural selection is imperfect, since brain disorders are far more common than even appendicitis. At least 1 percent of the population suffers from epilepsy, another 1 percent from schizophrenia (those are the underestimates -- double them if you're a pessimist), and the figures for depression range from a few percent up to 15 percent, depending on how you define what you're counting. A sizeable fraction of the cases of each of these major brain disorders seem to be inherited, though only as a predisposition rather than a sure thing. How did they escape natural selection?

One possibility is that they're linked to traits that are useful, so that eliminating them would yield an overall reduction in fitness rather than an improvement. For example, boredom and schizophrenia are related in the sense that schizophrenics often cannot stick to a subject: thoughts intrude into their attempts at conversation, or they may hallucinate, hearing voices give a running commentary on their actions. It's as if the boredom mechanism had run wild, allowing subconscious thoughts such easy access to language consciousness that one becomes like a compulsive TV channel-changer flicking from one program to another after only a few seconds. I don't think for a moment that schizophrenia is as simple as a misadjusted boredom parameter, but there are aspects of it that could be interpreted this way.

Epilepsy in baboons has escaped natural selection: some subpopulations of Papio papio have photosensitive epilepsy, in which rapidly flickering lights trigger a seizure. A forest animal such as the typical monkey often experiences flickering lights, as it runs around though patches of sunlight and shadow; thus, photosensitive epilepsy in a diurnal forest animal would probably be selected out. But the baboon is a monkey adapted to the savannah, where the trees aren't densely packed: baboons simply aren't exposed to flickering lights very often, so that any epileptic tendencies that by chance develop in evolution are not promptly edited out.

In humans, some forms of epilepsy might be side effects of an improvement in neural machinery that has proven so successful that it hardly matters (to evolution, not the individuals affected) if 1 percent of the population has a problem. For example, temporal-lobe epilepsy is a common form in humans, though no animals have been found to naturally exhibit it. We can often cure a patient with this form of epilepsy by simply removing the tip of the temporal lobe (a plum-sized chunk of brain tissue); surprisingly, no function disappears after the removal. Indeed, it is hard for observers to tell that anything is different about the patient (except that the seizures have been reduced or eliminated). The tip of the temporal lobe and the premotor regions of the frontal lobe are, it so happens, the prime candidates for locations in which many of the brain's extra borrowable sequencers are located, augmenting precise timing via the tandem arrangement. Because those extra sequencers are not essential except when actually throwing (so my theory goes, at least), that might explain why removing such areas seems to do so little to normal function. (Throwing accuracy, alas, is not usually examined by neurologists!)

And this also helps explain why the temporal lobe is so prone to epilepsy in the first place: seizures get started because a group of nerve cells go into a wild oscillation, rather like my washing machine at home when it gets to the spin cycle but all the towels are on one side of the drum, unbalancing the load. Timers are, of course, natural oscillators. A lot of them, particularly if hooked up to synchronize with one another (as I postulated for the "get set to throw" phase of throwing), would be a natural setup for a pacemaker that could drive the rest of the brain into a seizure. Correct or not, this little story illustrates the quandary in which evolution might sometimes be placed, where it has to take the bad with the good.

For such reasons, natural selection may be unable to act against seizures: the bad things are too closely linked to the good. There are other possibilities, too, such as a lack of enough time to select out the bad traits (if they'd developed recently in evolution). Or perhaps they're just not "exposed" to natural selection at a time when it will affect inheritance. And that's probably the key to why many kinds of depression have survived in evolution: depression often develops at an age when people have already had all their children. Initial hospitalizations for severe depression peak at age 55 (in contrast, for schizophrenia in males, the peak is at age 18 and for females at age 29, showing why one has to seek other explanations for schizophrenia escaping natural selection). While grandparents are quite useful in most human societies for both wisdom and babysitting, it's not the life-or-death usefulness of the parents, who forage for food and suckle the infant. And so late-appearing traits often escape natural selection -- there is simply very little feedback into the gene pool when something goes wrong at age 55 or 70.

INDEED MUCH OF AGEING may be a similar problem of late-blossoming genes that have escaped natural selection over the generations. There are a lot of genes that are normally kept "repressed," their DNA sequence literally masked by a protein, so that RNA copies of them cannot be made. Only when certain conditions are met is the repressor removed so that the enzymes and other proteins can be manufactured from those genes. For example, there are DNA codes for several kinds of hemoglobin, one common in the fetus and the other a version that gradually replaces the early version; both carry oxygen just fine. The genes for fetal hemoglobin are still there, it's just that they're largely repressed with age, and the adult hemoglobin (repressed during gestation) is gradually expressed more and more during the changeover.

And similar transitions from one version of a gene product to a closely related form are probably common throughout life and in many body systems (the gene for making the enzyme that digests milk is repressed in some adults). Such gene repertoires, rather than wear and tear, may be responsible for most of the changes in body appearance by which we can estimate someone's age: the shape of the face and relative size of the head, compared to the rest of the body, are prime clues to the age of children, just as wrinkles and a broadened waistline are clues to whether someone is 20 or 50. In juvenilization among the primates, all life stages are slowed: not only are the periods of gestation, infancy, and childhood doubled, but adulthood is too. If a longer lifespan were really desirable, the logical way to achieve it would be to slow down the sexual and somatic clocks. They're likely what control when new versions of a gene are ushered onstage.

One of the major hidden manifestations of ageing, seen from adolescence onward, is a decline in many of the neurotransmitter substances used by one nerve cell to signal an adjacent one. Since nearly all nerve cells are sensitive to the balance between plus and minus inputs rather than the absolute size of each, this decline may have no discernible effect on function; both plus and minus inputs might decline by half between ages 20 and 70, but that won't necessarily change a zero balance. Yet let one decline by a greater percentage than the other, and the system would somehow have to compensate in order to keep things running properly. In Parkinson's disease, the substantia nigra (an almond-sized collection of pigmented nerve cells below the thalamus) is affected -- a viral infection might, for example, kill off half the nerve cells in that location at age 30, seemingly without consequences for function. But when the age-related loss of 5 to 7 percent of its nerve cells per decade adds up, and one gets down to only 20 percent remaining, then one starts getting symptoms of rigidity, tremor, and all the rest. Why won't the system run on just 20 percent? Maybe it's the Law of Large Numbers again, too much fluctuation about the same mean. Just too noisy.

Now, the "normal" 25 to 35 percent loss of neurons from the substantia nigra in adulthood is not the same in other brain areas; right next door in the reticular formation, the loss may be minuscule, with 98 percent of the original cells still there at age 70. What controls this loss rate? Probably gene expression, rather than exercise or virtuous living -- but, in fact, nobody knows yet.

Depression, with its rising incidence with age, may be caused by genes that are expressed late enough along life that natural selection affects only the individual and not his descendants too. Those versions of the genes just haven't been improved for us by our ancestors. We owe our good health up to age 45 to our ancestors, but particularly to those would-be ancestors who dropped out because of natural selection before adding very many of their genes to the common pool. After age 45, it's a whole new ballgame, played with few evolutionary rules because natural selection has not operated on those particular combinations of expressed genes. Indeed, if there is a cutting edge of human evolution these days, it's in that post-reproductive age group that lives largely unrestrained (as well as unprotected) by the usual evolutionary constraints that have shaped our species.

The secret to birthday happiness is learning to accept the ageing process as something as beautiful and natural as premenstrual tension.

Mile 171
Gateway Rapid

THE STAIRWAY-WILLOW SPRING FAULT cuts across the Canyon here so that we have two side canyons emptying into the river at this point. Like Badger Rapid back on the first day, that's a good setup for a major rapid -- but Gateway Rapid is only rated 3 these days.

One can see that the two sides of Stairway Canyon are offset; the layers on the downriver side are jacked up nearly four stories higher than on the upriver side. I hear that we're going to see lots of fault lines later today and again tomorrow. The Colorado is now cutting into the Bright Angel Shale once again; I wonder if there are any more big landslides like the one that created Surprise Valley?

Up and down, but always different.

We're also seeing new plants now, such as the creosote bush. Cactus everywhere. Bighorn somewhere, it is claimed. But I'm still watching for rocks that move.

The clouds are still with us, but I think they're starting to clear. It'll probably be hot by the time we get to Lava Falls, and get cooled off in a big way. There's a lot of joking about Lava Falls this morning, gallows humor and the like. Someone's offering to make book on whether there is really a black hole there. Might as well bet on Clams Linguine.

There are clouds over some people's lives because they're "born wrong." We're all different, but there is a tendency to regard variations well away from the average as imperfections. We live in a world where variations suggest manufacturing defects, where people unable to learn to read suggest an error of development, an unfortunate gene, an unwelcome occurrence. But are they, perhaps, merely evidence of nature's method, of producing lots of variations and letting the marketplace decide? Once upon a time, a miswired visual cortex was probably better at color vision, and so those lucky monkeys that had it turned out to be better at spotting fruit among the leaves.

We may come to look upon much of mental illness this way, as the product of variants in the wiring of the brain much as reading disorders probably are. And some such variations are hard to get rid of, if they're late-blooming.

SPEAKING OF DEPRESSING SUBJECTS, how about pain? There are indeed some obvious relationships between pain and depression, between suffering and consciousness.

For what reason might the following collection of behaviors be appropriate? Lethargy, daytime sleepiness, loss of sexual drive, loss of appetite, and a tendency to not move around much? It matches up with how an injured deer behaves, when it holes up for a week without moving, to give healing a chance. And it isn't just deer -- that's how most of us act in the days following an injury.

It is becoming evident that this behavioral syndrome can be triggered in other ways, some inappropriate. Our pain system really isn't very sophisticated: a toothache may, for example, trigger the "holing up" behaviors, as may neuralgias -- neither of which will be helped by these behaviors.

Now this collection of behaviors constitutes a very characteristic part of the mental disorder we call depression. Does this mean that depression is partly an inappropriate response to a chronic pain of some sort? Certainly the converse is frequently true: pain specialists have learned to using the antidepressant drugs to treat chronic-pain patients when aspirin fails, having found that these patients will often improve behaviorally -- and that their pain may also disappear at the same time. As Rosalie pointed out, this suggests a research strategy that would attempt to persuade the brain that a physical pain, or even a psychological "pain" of the type we honor with such phrases as "a pain in the neck", is not important, that it is inappropriate to respond to it by holing up. One can see why treatments such as psychotherapy might work.

Of course, depression is more than just holing up. Melancholy feelings are an important, though not essential, part of the depression syndromes. And this brings up the distinction between the phases of pain. We pain researchers (well, I guess that I'm the only one on this trip) are finding out an increasing amount about the specialized neural pathways for signaling and evaluating sensations that may be associated with tissue damage. Those "fire-alarm" types of sensation are obviously useful; you'd expect them to be about the same in a deer as in a human. But they don't always cause distress: 37 percent of the emergency-room patients studied in a Montreal hospital didn't report pain for hours after being injured, despite broken bones, major abrasions, and other reasons why their sensory neurons should have been carrying quite a lot of pain messages to the brain. That's why neurophysiologists distinguish "nociception" from "pain": pain is what one reports (sometimes) when nociceptive messages arrive in the brain. It makes evolutionary sense for sensation to be sufficient to tell you to get yourself out of the situation -- but you certainly wouldn't want the holing-up phase to start right after the injury! And fortunately, the tenderness of an injured region doesn't develop immediately afterward but is instead delayed by hours.

In addition to nociception and pain, there's suffering. It is greatly augmented by the predicting-the-future aspects of consciousness; we can see what's coming, and so may be additionally distressed above and beyond anything caused by the current reports from our sensory nerves. We suffer less if we know that the sensations of pain will be short-lived (as in a dentist chair) or innocuous (as in breaking in a new pair of shoes). But according to the scenario-spinning theory, human consciousness may be greatly enhanced over that of the deer, and that might enhance our suffering. Thus, even though the evolutionary perspective says we need not ascribe to animals quite the same extent of "suffering" that we would feel in a similar situation, the animal might feel more "pain" than we do in the short run, simply because it is unable to know that a pain is innocuous or will be short-lived. How these factors balance out in terms of distress produced is hard to predict; sometimes you just have to watch the animal's blood pressure for signs of alarm.

We are just starting to look at pain and suffering from a biological perspective, asking what role they really play in animals, asking what are the normal phases of response to an injury. So far, it looks as if the initial pain sensation (what most researchers study, what most physicians test, and what the analgesic drugs affect) is the least of the problems, as its function is merely to prevent further injury. It's the delayed tenderness and the prolonged holing-up syndrome that create most of our problems with pain (outside the neuralgias, which falsely report an injury when none exists) -- and they may be related to some common types of depression. Beyond all that is suffering, and we don't know the extent to which animals share it with us.

Our brain and sensory nerves really aren't very good at reporting tissue damage accurately, either its exact location (can you tell exactly which tooth hurts?) or its magnitude. All sorts of errors occur, as when a heart attack is felt as a pain in the left arm instead of the chest. But maybe it just wasn't very important to know the exact location of a pain, in the days before doctors, when we were being shaped by evolution. If pain's first function is to change our activities so as to help stop the damage, it isn't critically dependent on accurate estimates of position and magnitude. "Good enough" engineering strikes again. In pain's second function -- to aid healing during recuperation -- an on-or-off type of tenderness report is again almost as useful as a detailed accounting of the damage. In evolution, one didn't need to know where an injury was exactly located in order to repair it -- one's body does that automatically, without being consciously dispatched to the exact location of an injury.

When you get down to it, you realize that pain simply hasn't been exposed to a lot of selection pressures -- except, perhaps, for distracting false-alarms. But malfunctions like neuralgias are again mainly confined to postreproductive phases of the life span and so have escaped selection.

This evolutionary analysis helps one to better appreciate the senseless, inhuman things such as cancer pain, in which there seems to be no natural way of turning the pain off after it has served a warning function. Evolution may have provided a cutoff switch for short-term pains such as those a tired athlete feels, so that they do not interfere with getting out of a threatening situation, but evolution hasn't provided any cutoff switch (so far as we've been able to discover) for the long-term pains of tenderness during repair attempts. After all, during most of evolution, a serious injury was life-threatening -- either you got better or you died. And so humans have, until recent years, had to live with Seneca's sage advice: "Ignore pain. Either it will go away or you will."

Pain control is one of the most significant ways in which we can improve the quality of our lives; it is a far more humane goal than merely trying to extend the lifespan. We will be taking evolution into our own hands even more than usual in this area: nature hasn't done much, and our measures will strongly interact with whatever quality-of-life goals that we set for our society.

THIS LOWER SECTION OF THE GRAND CANYON is certainly starting to look different. There are lots of piles of landslide debris, high up. But the Canyon walls are also studded with patches of green, the plants growing among the red rock. It's the way one can tell the difference between pictures of the lower Grand Canyon and the same layers in the upper Canyon, at least if it has rained recently. We're at lower elevations here, with less severe winters, and the plant population is shifting over to a collection more like the Mojave Desert's.

In Jimmy's boat up ahead, someone is joking about us drifting toward our very own appointment with natural selection.

A gray day.

For days you have been hearing rumors about That Riffle-At-Mile-179.6. Lava Falls. This rapid offers the true test of a geologist's loyalty to his science. Will he, in the face of such an improbably violent rapid, be able to notice the cascades of black lava that once poured into the Grand Canyon and froze onto its walls? Will he examine this rock with its small olivine crystals, glassy matrix, and columnar joints, and conclude that it must have cooled quickly after flowing into the Canyon? Will he notice the cinder cones on the Canyon rims above? Will he remember that this rock is only a million years old, making it the youngest of all the Canyon's rocks? Probably not.
......MICHAEL COLLIER, Grand Canyon Geology, 1980
BLACK LAVA appears suddenly, but subtly, at Mile 177. There are a few boulders of lava disguised in a talus slope of ordinary rock coated with dark desert varnish. By geologic standards, this lava is quite recent compared to all other rock in the Canyon -- such as the Cardenas lavas back at Furnace Flats from 1,200-million years ago. This lava is from the last several million years, which saw the ice ages and the threefold enlargement of the prehuman brain; it is left over from a giant lava flow that dammed up the Colorado River near here -- and nearly filled up this part of the Canyon with muddy water. That lava up there at the 100-story level above the river is probably left over from that great lava dam. Influenced by Edward Abbey's vision of the end of the Glen Canyon Dam and Lake Dominy, we joke about what a sight it must have been when the lava dam broke. One of the boatmen wears a campaign button on his cap, reading: "I Want to Run DOMINY FALLS, Glen Canyon."

A giant black rock about five stories tall sits in the right side of the river channel. Vulcan's Forge was once a volcano itself, which one day started to make the river boil. And then emerged in mid-river. Now it is a chunky remnant called a volcanic plug, a reminder of how fast things can come and go. We hear that there's some real marble hereabouts -- contact metamorphism, just like what made that asbestos we peeled off the rock back at Deubendorff. Except this time it was limestone that got heated, and metamorphosed into marble rather than asbestos or schist.

This morning on the river has been very quiet. There have been no serious rapids, not one. Indeed, we've seen mostly riffles and whirlpools for almost 30 river miles. Now the Canyon is opening out, great flows of black lava sweeping down the right canyon wall to the river bank. The river is widening and slowing in anticipation of the biggest rapid on the river; the boatmen call this stretch of river "Lake Lava," and they row harder, getting warmed up for the big event.

Soon we faintly hear the low, continuous rumble of a distant thunderstorm. But the clouds are clearing, so it's probably Lava Falls announcing itself.

A black hole in Lava Falls? Surely they're joking. Ahah! I'll bet it's a hole surrounded by black lava rocks. That must be it. That, or maybe an allusion to another property ascribed to black holes: the tendency to not give back what they take in.

It is important to understand that you don't get splashed in Lava Falls; you get inundated. Eating a wall of solid water is one of the quintessential experiences of running this rapid. Not a few river runners have distinctly recalled being in a boat but completely underwater and unable, for a few tense seconds, to breathe. In one astonishing run a boat flipped over on one wave and back, right side up, on another. It required a film, taken from shore, to convince its occupants, who had never left their seats, that they went completely around.
.......ROBERT O. COLLINS and RODERICK NASH, The Big Drops, 1978.

Mile 179
Lava Falls Rapid

THE BOATS are all pulled up on the right shore, in the midst of a grove of seepwillows. Climbing upward along the black gritty trail through the lava, we are soon in the hot sun, the clouds having parted, the heat of midday approaching. The black rocks are too hot to touch, the lava too prickly for comfortable handholds anyway. But the trail is easy and leads up only far enough to give the boatmen a good vantage point from which to plan their run of the rapid.

We leave the boatmen to themselves, standing on their advanced perch discussing possible routes with much pointing and waving of hands. We stand back on the trail, engulfed by the heat beating down from above and rising up from the hot black rocks beneath our feet. The pounding of the rapid is ceaseless, the loudest we've experienced -- it is a low vibration that penetrates your body, from which there is no escape.

Lava Falls at Mile 179.6, from Leonard Thurman's Grand Canyon River Running web pages.

Lava Falls is well named: it looks more like a waterfall than any rapid we've encountered before. Crystal, the worst so far, dropped the river level by one and a half stories. Lava Falls drops three stories, almost four. And it doesn't take very long to do it, either: it looks like a short and harsh staircase, filled with boulders. There are a number of foaming holes scattered along its course, some to the left, others in mid-channel, others along the right. Black rocks dot the right side. All the holes seem surrounded by black rocks. There is one particularly large black rock just downstream of the last hole in the right channel, but there is no water going over it.

Motor Rig running right side of Lava Falls at Mile 179.6, from Leonard Thurman's Grand Canyon River Running web pages.

We evidently cannot go straight down the middle at this water level. One way or another, the boatmen will have to ferry sideways across the river: after passing to the right of the hole near the top, one would have to ferry left to avoid the big hole just ahead. But not too far left. I can spot no obvious safe path through the rapid. But then I'm not a pro. We amateurs trade proposed routes while waiting for the pros to finish doing the same thing. As we compare, I notice that the top left hole has changed, just in the 15 minutes since I first looked.

Though the boatmen still show no sign of finishing their planning -- they're still spinning alternate scenarios -- many people have gone back down to the boats. The view, together with the vibration, has convinced people that Lava Falls is not like other rapids, that maybe it deserves its reputation. I take a last picture and then head down myself. It's too hot and exposed up here, almost a lunar landscape. It is quieter and cooler at the boats, and they are comfortingly enclosed by shade-giving greenery. People are pretty quiet and certainly sober. One of the teenagers manages to look bored.

Without prompting, we are starting to tie down everything, tightening up on the nylon webbing that holds our ammo cans and bailer buckets in place. It is all too easy, after seeing Lava Falls, to believe the boatmens' cautions about securing everything.

Life vests are refitted, straps tightened far more than ever before. Most people lash their hats down to the raft somewhere, imagining the force of the heavy waves will be too much for their light brims. Perversely, I just tighten my chin strap and hope that my heavy hat brim will shield my face as it has before. I try to pull my knife out of its sheath and am surprised at how hard I must maneuver it before it comes free. First I tie the sheath more securely into the webbing of my life vest, so that I have something to pull against if I want to get the knife out. Then I brush off the sand adhering to the knife and sheath. I slide the knife in and out of the sheath numerous times, to loosen up the leather's grip, leaving it fitted just tight enough so that it won't fall out. Knives aren't on the official packing list, but some years ago a neurobiologist I knew, Donald Wilson, was drowned when he was held underwater by a rope in a white water accident in Idaho; he worked in the same subfield of neurophysiology as Dan Hartline and I, and we often discuss one of his last discoveries, about simple ways of generating rhythms, one of the first emergent properties discovered about neural committees.

Sandy reappears and the other boatmen can also be heard among the seepwillows, heading to their boats. I am glad to be riding with Sandy Heavenrich today. He is probably the strongest of all the boatmen, and that could make the difference in Lava Falls. I ask him what route he is taking. "Enter left, ride the lateral wave right, hook around that top right hole, ferry left to avoid the big hole at right bottom." Sober as ever, Sandy looks around, double-checking our preparations. He coils the mooring line, gives it a thump against the side of the boat to shake loose the sand, and swings onto his seat atop the freezer chest. Then he repeats the lecture on high-siding and what to do if you find yourself out in the river. And to please be sure to avoid foreign entanglements.

As we row out into the river, I surmise that we're to be the lead boat through Lava. We're the guinea pigs who get to test the currents. But the boatman who leads usually takes a conservative route -- it's the boatmen further back in the order who get a chance to try the fancier routes, once they have someone downstream to catch them if they get into trouble. There are three boats in our group, but the other two are holding back, probably to see how we do before they start. Gary Casey is standing out on the rocks at the lip of the rapid, ready to watch us descend. He'll tell the two waiting boats what happens to us, as they won't be able to watch us.

The passengers from the other four boats will watch us from shore just as at Hermit's photo run, then come through afterward as we watch from shore downstream. As we row back upriver to position ourselves in the left-center of the channel, I see some temporarily-reprieved passengers from the remaining boats climbing back up the hot lava path carrying cameras with telephoto lenses.

Sandy leans over to check the spare oars, strapped to each side of the boat. The straps are usually tied so that one pass of a knife can liberate an oar quickly. But Sandy has arranged them today so that pulling a simple shoelace knot is sufficient to free them up. He carefully instructs the rear passengers, Laura Sirota and me, to pull the knot only if he shouts at us to do so. I have heard that Lava frequently gets hold of an oar, snaps it out of the oarlock, and doesn't give it back. But Sandy doesn't mention that. He is strong, silent, and very competent.

Entering Lava Falls at Mile 179.6, from Leonard Thurman's Grand Canyon River Running web pages.

We approach the lip of the rapid at left center, our stern pointing to the left shore slightly upstream -- evidently Sandy is thinking ahead to the hard left turn he'll have to execute off the right shore after the lateral wave carries us to the right, past the top of the boulder with the hole. So Sandy is initially pushing on the oars to advance the bow of the boat to the right, a weaker stroke than the pull he'll need subsequently to make the U-turn off the wall-- but Sandy's push stroke is as strong as many a boatman's pull stroke. Laura takes off her glasses, folds them hastily, and buttons them into a pocket. As we perch on the lip, I am surprised how far down the rapid I can see -- this is really a steep gradient compared to earlier rapids. It's like looking from the second balcony down to the stage of a theatre. And then we take the first step -- which is nothing like the gentle beginning of most rapids. Suddenly water seems everywhere around us, glittering in the sunlight. We are instantly soaked.

We are swept into the right lateral wave with a flourish of wake-up waves. Sandy immediately begins pushing hard and fast. He is trying to pick up additional rightward speed. And indeed we speed up. Another wave soaks us. Sandy is rowing faster than I've ever seen him row. But we are too slow and I see that we are being carried downriver toward the boulder faster than we are heading into the turn. That's not in the script. There's a hole below that boulder.

It's like seeing a skidding car heading toward you, one that you cannot evade, and just knowing there will be a collision. Like a crazy dream in slow motion, in which you're trapped, helpless. Nonsense -- this can't happen to me. Yet the boulder is almost beneath us and the drop into the hole is imminent. Well, I always did wonder what it would be like.

Slowly we fall. The boat twists and arches its back. As we splash into the frothy hole, white water is everywhere -- in the boat, outside the boat, soaring over our heads, scattering the sunlight. Our right oar is pushed back against the boulder, trapped between us and a hard place. It irresistibly pops loose from its oarlock, is torn out of Sandy's strong grip. The waterfall pours into the boat -- I cannot see Laura anymore. She's under the waterfall. Then we spin around, and she reappears, shaking her head. Then I see the long oar flapping around alarmingly at the end of the short leash tying its shaft to the frame. I push Laura down; she is too close to grapple with it safely, even if she could see without her glasses. I reach across her stiffarmed in an attempt to fend off the oar or grab it. Sandy briefly makes an attempt to retrieve the flailing oar but soon leaves it to me, shifting both hands to the remaining oar, pulling hard each time, trying to get a bite on the frothy water.

The sunlight returns and I realize that we are out of the hole. Just like that. But we are still in the midst of Lava Falls, and the river below the hole seems only slightly less frothy than the hole. The oar still escapes me; I grab only water, repeatedly. I am still leaning across Laura; she must be wondering what is going on up above, what is taking me so long.

Swift currents again carry us downriver through smaller rocks, and Sandy is trying hard with his one oar to get us out of the right channel, back into the middle of the river somehow. And away from the big hole. But we are too slow again trying to ferry sideways, and are drawn back into the right channel.

Oh, no -- not again! Haven't they ever heard of acquired immunity? It can't happen twice to me. But again we approach a precipice. The boat perches briefly atop the big boulder. And we twist and fall -- a real drop of perhaps half a story -- into the exploding waves, which batter us from all directions. At least we don't flip. By this time I have given up on the loose right oar and am again crouched down in my left rear corner, wedging myself in as tight as I can. Laura is still positioned with her head well down, and the loose oar is hard to see, what with all the airborne water. The boat is folding, filling with water, lashing around and spinning. We are bashed about, seemingly stuck in the hole, just like in the stories we've heard. With the lone oar, Sandy is valiantly trying to get a bite on some solid water with his two-armed pulls, but hits only froth. Again and again.

I remember the black hole story -- once you're in, you can't get out again.

And there is no shape or form anywhere -- I cannot see either Sandy or even where I'm holding on to the boat frame, there is so much white water everywhere. It might just as well be black for all the good the light does. But then there is even more water. And the light does begin to dim. I sputter as I try to breathe.

I returned, and saw under the sun, that the race is not to the swift, nor the battle to the strong, neither yet bread to the wise, nor yet riches to men of understanding, nor yet favor to men of skill; but time and chance happeneth to them all.
......BOOK OF ECCLESIASTES, about 200 B.C.

AND THEN WE'RE LOOSE, who knows how. Maybe it just spit us out! We've been rejected! We come up for air and see real sunlight, snatches of riverbank scenery through the white water. Sandy now effortlessly grabs the loose oar and together we fit it into the oarlock. Laura is sputtering. After I stop leaning over her, she comes up wiping water away from her face, opening her eyes to see where we are. We are safe. The rapid isn't over yet, but we're safe. We start bailing out the thoroughly filled boat, though I must loosen my lifejacket corset straps to bend easily. My hat is still wedged on tight, and I push it back with relief, free at last.

Sandy rows us over to the right shore in the first quiet cove of swirling waters. Laura fishes her glasses out of her pocket, puts them on still wet, and looks around. We look back at the path we traveled and try to comprehend what we've been through. At least we missed all the holes in the left and center channels. We are looking up at three stories of white staircase and the two big holes that we survived. It seems quite absurd.

"I'd say we got kind of thrashed back there," opines Sandy with a big grin. "See them looking down at us?" He points upstream and then gives a prizefighter's victory wave to signal that we're okay.

Another boat is seen hovering at the top of Lava Falls, seemingly backpaddling. They couldn't see what happened to us. But presumably Gary, standing on the shore near the lip of the rapid, has shouted to the next boatman that the rightward lateral wave at the entry point is much slower than anyone guessed. Plans are probably being revised with much shouting back and forth.

Sandy has the other passengers disembark after we've finished bailing, and then prepares to play rescuer. He climbs up front and ties a long, medium-diameter rope into the D-ring of the boat's bow and tests the knot. Then he beckons me to come forward and hands the coiled rope to me. As we row back upriver and position ourselves behind a small boulder that affords some shelter from the swift currents, Sandy explains the different ways we might use this line. I can throw it to a swimmer (I haven't practiced with a lasso since childhood, however). But we have to be careful to keep the swimmer downriver of us -- someone approaching from upriver will be carried under our boat by the current as we attempt to pull them out. Therefore, I should guide them around the bow to the downriver side before trying to haul them into the boat, says Sandy. We might also use the line to tow another boat.

I practice throwing the line sidearmed at a small rock in the river and, while overshooting more than I intended, do lay the line across the rock. I re-coil the wet rope with care, probably having exhausted my beginner's luck. I'm still annoyed with myself for failing to retrieve that oar, back between holes.

So, positioned behind our boulder by Sandy's regular push strokes, we watch the other boats come down Lava Falls. The next two make it look easy -- though they ship a lot of water somewhere. They too take up rescue positions on the opposite shore, one opposite us and the other further downriver, each boat bailed dry in an intense flurry of activity by all passengers.

There is a long wait as the camera-laden passengers of the second group disappear from the trail's vantage point and get back to the four remaining boats. I am surprised that no one decides to walk around Lava -- it's easy enough to do -- after seeing our travail. We can no longer see them, but we imagine them rowing back upriver to position themselves in the center left of the river. Nothing happens for a long time. Sandy and I finally begin to joke about them rowing all the way back up to the volcanic plug -- maybe even to Phantom Ranch! But then a boat appears on the horizon at the lip of the rapid and starts down the staircase, ferrying out of sight, then reappearing in the center channel.

It is not at all like the slow-motion of our ride down the rapid. In just a minute or so they zip past us -- very wet but exhilarated. Soon they are bailing like crazy.

Indeed, all the boats make it without apparent incident, some taking a markedly different route than we'd planned, none following our white staircase, none needing our towing and pickup services.

The other two waiting boats take off, following the last boat through. But we're delayed, having to detour to shore to pick up our three happily stranded passengers with their cameras. We belatedly follow the other boats downriver, passing through Lower Lava Rapid alone. A mere 5. But enough so that we have to bail the boat again.

EVERYONE ELSE is clustered on a narrow Muav ledge on the left bank a mile below Lava Falls. It looks like an elevated stage filled with actors. Our late arrival is welcomed -- we feel as if we're on stage. It appears that everyone has been talking about us, awaiting our delayed solo appearance.

We head for the lemonade. To hear the second group tell what they saw from shore, our trip was even more harrowing than we thought. We were out of sight in the holes and didn't reappear promptly, causing some concern. Sounds as if they were holding their breath from anxiety just as much as we were, to keep from breathing water. They saw our boat arch its back and then fold the other way, saw our oar flailing around at some point (Joanne Kerbavaz says she got a telephoto shot of us, just when we lost the oar in the first hole), saw us miss the middle channel and be swept back toward the second hole, sinking in it out of their sight. We, of course, are rather nonchalant, as if it were all in a day's work. Even the black hole. Our lemonade cups only shake because we are a trifle chilly from our soaking.

I can imagine the anxiety about going through Lava that our run must have triggered in the remaining six boats. But the only real casualty of Lava Falls was Ben, who had been thrown backward so hard by a wave that he got a bloody nose from a collision with the boatman's knee. Alan's knee looks unscathed.

Soon lunch is ready. Everyone is talking animatedly, the boatmen are exuberant. I think that the adrenaline is still running high. Lava Falls is past, it's history, it's done. Finished. I've never heard the group so lively.

And we are in no hurry to go anywhere for a while. Seconds on sandwiches become thirds. People keep dropping sandwich fillings because they're trying to gesture while they eat. Two ravens hang out nearby, offering to clean up if we'll just move. Sandy mixes up a second cooler of lemonade because the first one ran out. We exhaust the cookie supply, even the two buckets of oranges and apples.

And the flat, shaded ledges of water-sanded Muav limestone are comfortable. Some of us stretch out, nap for awhile.

To the Primal Wonders...you shall win them yourself, in sweat, sun, laughter, in dust and rain, with only a few companions.
.......NANCY NEWHALL, 1960.

A SNAKE PASSED ME BY. Larry Anderson awakened me, saying that a long, lovely snake had just zipped past my head. It is now hiding in a low miniature cave nearby, formed by Muav layers just overhanging the stage on which we're spread out. He couldn't believe how fast that snake moved. That rather eliminates the possibility that it was a Canyon rattlesnake, since rapid locomotion is not one of its attributes. So I bend down on hands and knees and look in where Larry points. But I cannot see the snake for the longest time. Then it flicks its tongue twice and I see it in my peripheral vision. Snakes do that to sample the air -- when the tongue arrives back home, it is inserted into the roof of the mouth and tasted. A funny way to smell, but it saves inhaling. The snake presumably smelled us that time.

What a lovely snake! It is khaki or perhaps a light reddish-brown, a perfect match for the Muav. It is also exactly the thickness of a limestone layer, so I have trouble following its body along the twists and turns of the staircased ledge on which it is stretched out inside the "cave." The snake looks like a little strip of color-matched molding clay tacked onto a lip of Muav. At one point, its body drops down to the next-lower ledge -- looking just like a flexure in the rockbeds. Finally I locate its tail, after five false alarms. Superb camouflage. Snake and undulating ledge look like a rhythmical, subtle sculpture. Larry and I estimate its length at nearly 1.5 meters. If Larry hadn't seen it enter the low cave, we'd never have spotted it. Except for waving its tongue occasionally, it is in perfect repose.

I pick my way among the sleeping bodies to where Alan is sitting alone on his boat, and quietly describe the snake to him. "Probably a Red Racer," he says, showing absolutely no inclination to get up and come look. I think that the letdown has finally set in. Post-adrenaline lethargy. I see that another bucket of fruit has been put out, and help myself to an orange.

I get back and -- once I finally relocate him, about an elbow's length from my face -- find the snake still there, tasting the air again, blending in perfectly with the layers of limestone, waiting patiently for a lizard to walk past the entrance to his cave. Larry and I sit back at the river's edge so as not to scare away any foolish lizards. For a good half hour I stare, hoping to either see a lizard arrive or the snake leave. Nothing happens. The shadows change, the river rises a little, people stir.

People seem not to bother the Red Racer at all. People are temporary, lizards are forever.

EVENTUALLY we get ourselves together but, before casting off from our homely Muav ledge, Larry and I look inside the low cave once again. It takes a while to double-check all the possibilities, but it seems that the Red Racer has disappeared while we weren't looking. Larry says that at the speed it moved earlier, ignoring it for three seconds might have been enough. I am disappointed, having wanted to see its racing act for myself.

BUT THE BLACK HOLE OF LAVA FALLS wasn't really either of the holes we inadvertently explored, J.B. tells us as we get ready to start off downriver again. Appropriately enough for a black hole, we couldn't see the Great Black Hole of Lava Falls -- though that's because it only exists at really high water, as during the Fool's Flood of 1983. That big black rock at the lower right, which we glimpsed downriver as we swirled around in the second hole, can have water pouring over its top when the river is really big.

The big black rock creates a monster hole and a giant back-eddy, that reaches downriver even further than the spotter rocks that we hid behind while watching the other boats come down. Double the river's speed, as can happen at high water, and the size of an eddy may increase eight times. Order-from-fluctuation thermodynamics strikes again. Such a giant eddy is so strong that anything unlucky enough to be caught by it is inexorably carried back upriver, usually into the hole itself. And the high water also brings big lateral waves reaching halfway across the river, which similarly suck victims into the eddy. Sticks, even logs swept into the river by recent flash floods in side canyons, are trapped in the hole, which irregularly throws them upwards into the air, recapturing them as they fall, this stunning display of virility advertising, to all who watch, the unequaled strength and fury of this monster hole.

This last hole in the lower right channel, when it exists, is what deserves to be called a black hole. A boat swept into it would, the boatmen insist, have disappeared by having been torn to shreds (in 1983, the river companies often had passengers walk around Lava Falls while the boatmen took the lightened boats through alone). The Great Black Hole is surely the closest thing on the river to a Waring blender.

If Dante had seen a big eddy with a hole like Lava's, he would have had the perfect analogy for both Purgatory and Hell. The back-eddy tends to be a holding pattern, as one circles endlessly, only occasionally being swept back into the upstream hole. Once in the hole, one can't get out, and is really pounded.

My specialty is the time when man was changing into man. But, like a river that twists, evades, hesitates through slow miles, and then leaps violently down over a succession of cataracts, man can be called a crisis animal. Crisis is the most powerful element in his definition.
.......LOREN EISELEY, The Night Country, 1971
SOME RIVERS, such as the Middle Fork of the Salmon River up in Idaho where I first met Alan and Subie, are just plain downhill all the way, almost constant white water and a continual challenge. Others, such as the Colorado, are more of a staircase than a ramp. The impounded waters behind their rapids move slowly, then speed up as they shoot through the narrow and shallow confines of the rapids. Created by flash-flood debris from side canyons, the Colorado's rapids provide a regular challenge to the skills of the boatmen -- but give them a breather between such stresses.

We're coming to see evolution as a lot like the Colorado. It used to be thought a gradual process, a ramp like the Middle Fork, that continually edited an organism's gene pool -- whether bacterium, plant, or animal species -- so that successive generations were better and better suited to the environment in which the organism found itself. While Darwinian gradualism does exist in the isolated subpopulations, it is easily reversed -- it becomes unraveled, shall we say -- and the big picture is now more like the Colorado's staircase. A long period of quiescence like Lake Lava, then a short period of stress where certain skills and snap judgments are all-important, then a high-siding period of swirling waters as the river seeks a new course and untangles its various currents, and finally another placid lake which gives time for the boatmen to compare notes, practice techniques, think about how they'll handle the situation better next time.

Their skills are thus in excess of what is needed most of the time, just because they're essential on occasion. We too have skills far in excess of our everyday challenges, simply because our ancestors needed them to get through the staircase of the ice ages.

The most common recurring challenge is, however, called "winter." Most species of both plants and animals live in the tropics, where they're never exposed to freezing weather. A week of freezing weather could wipe out many species of tropical plants -- one of the things that makes the nuclear-winter scenario so scary. The plants that do survive freezing have learned to take the hints provided by cooling autumn weather and shortening periods of daylight, preparing themselves for the final onset of frost -- although sudden, unheralded frosts can still kill them. Leafless, the dormant plants aren't very nutritious to eat -- except for grass, accounting for the popularity of grazing. Many animals that live in winter-prone latitudes have developed behavioral strategies to get themselves through the winter. Some hibernate, living off their body fat. Some store food externally, like squirrels. A few depend on eating other animals that do one of these things, and so get grass and nuts secondhand, with fewer than 10 percent of the original calories left.

Thus, the tilt of the earth's axis of rotation has probably been the most regular contributor to the evolution of more complex animals. Many present-day tropical animals may have been though the winter editing process, skills such as extra cleverness in food-finding making them successful competitors against their ancestral species when they migrate back to the tropics. To see an animal in a tropical setting and assume that that's where it first evolved is probably one of the more common mistakes in biology.

While winter is the most common challenge to an animal that hasn't permanently moved to warmer climates, the decade-long fluctuations in climate surely hold second place. Even in the tropics, variations in the rainfall provided by monsoons can give rise to some hard years. The Anasazi of the Grand Canyon knew all about droughts. The years when Unkar Delta wasn't occupied match up with the decades that had poor rainfall, according to the tree rings.

A sustained dry period is usually blamed for the demise of the Anasazi, except those that took refuge near the present-day Pueblos. The Anasazi, who were flourishing in A.D. 1130 all the way from the humble habitations of the Grand Canyon to the great apartment complexes of Chaco Canyon, gradually disappeared over the next century or two as the rains kept failing. Much of the annual rainfall around here depends on the summer monsoons, the wet ocean air that drifts up over the land and releases its moisture in thundershowers each afternoon as warm air rises from the Colorado Plateau. But the thunderclouds are seen more often than their moisture is felt, because only small local areas -- a canyon or two -- actually get drenched. Unlike the frontal systems of winter which pass through, carpeting everything in their broad path with snow (although in the depths of the Canyon the snow often turns to rain or even evaporates before landing), the summer showers are hit-or-miss. In some decades, or even for some centuries, it was mostly miss.

On an even longer term basis, there are major ice age melts every 100,000 years, plus a lot of ups and downs in sea level. But that's a recent development, on the geological time scale. While there were briefly ice caps about 450 million years ago and again about 260 million years ago, the last 20 million years or so have again seen ice caps form as prolonged a cooling period has progressed. The ice ages occur when the ice caps become extensive, sometimes covering 30 percent of the land mass, but then the caps melt back every 100,000 years or so. This regular oscillation in the southern boundary of the northern ice cap has been pronounced only in the last 2 to 3 million years. Though it might be mere coincidence, that is also about the time that the hominid brain size began the enlargement that would carry it to 3.6 times the size of ape brains, more than three times enlarged over that of Australopithecus afarensis which existed 3 million years ago.

The ice age oscillation affected few, if any, other animals in the way that it seems to have affected hominids. For animals that live in the tropics, that's not too surprising, though there were surely climate changes in equatorial Africa as a result of the changes in ocean currents and therefore in weather patterns. One might be more likely to find changes in animals that lived in the temperate zones, but there again, no other known animal conveniently underwent a major enlargement of the brain.

And there is no evidence of hominids living in the middle latitudes until Homo erectus took up residence in Europe about a million years ago, in the caves near Beijing about half a million years ago. That's after the brain size had already doubled. "No evidence" may, of course, be due to the spotty nature of the fossil record; for all we know, hominid species were forged on ice age frontiers, but then found the living easier in the tropics.

Where natural selection takes place, where the subsequent population boom occurs, and where the hominid fossils are most easily recovered may be three quite separate places -- all may not have happened in the East African Rift Valley, as many anthropologists assume (and indeed may be forced to assume, in order to get on with testing hypotheses on the available material within their own lifetimes).

SO WHAT HAPPENS every 100,000 years? Does something throw another log on the fire, make the sun a little brighter? That seems unlikely from what is known about the sun. The sun has gotten brighter by about 30 percent since the earth went into business 4,600-million years ago. And while the energy released from the sun does fluctuate, the betting has always been on the amount of energy that actually reaches the surface of the earth.

Kepler realized that the earth's orbit was an ellipse rather than a circle. The change in distance from the sun causes the earth to receive about 7 percent less sunlight in some seasons than others. The ellipse changes, however, partly due to the attractions of Mars and Venus, so that the Earth's orbit varies from nearly circular (with no 7 percent annual fluctuation) to much more elliptical than at present, thus exaggerating the annual differences. Every so often, the ellipse stops flattening and heads back toward being circular. This was first realized in 1864 by James Croll, long before the ice age rhythms themselves were known in any detail. But with the aid of integral calculus, Croll correctly predicted that the effect would be small when averaged around the annual cycle; over the eccentricity cycle, the annual energy in the total sunlight we receive at the top of the atmosphere should differ by no more than 0.3 percent (the modern estimate).

The period of this eccentricity change is, however, about 100,000 years (actually a combination of rhythms of 412,000, 95,000, and 123,000 years). We now know it to match up with the dominant period of the glacier meltoffs, and that it indeed has stayed right in phase with them for the last six ice-age cycles. But the yearly energy received varies so little over the centuries that most scientists have difficulty imagining how it could cause such a large effect. The suspicion, of course, is that there is something about how the earth accumulates and melts ice that has a natural cycle close enough to 100,000 years so that the slight change in annual energy reaching the earth is somehow amplified in its effect because of this resonance.

Ice builds up over the years because the winter's accumulation is not completely melted off the next summer. While the freezing and melting of ice seems like a symmetrical process when dealing with the heat exchange that affects a tray of ice cubes, there are some significant asymmetries in the exchange when dealing with polar ice caps of great thickness and extent. For example, in a cooling climate, the ice in a glacier just keeps building up layer after layer, while in a warming climate, melting water may eventually drain off underneath the ice sheet and lubricate it, so that it will slip along the ground. The mountain of ice may then begin to collapse, spreading out by several kilometers within a few months. As it breaks up, more surface area is exposed to the warm air, speeding further melting in a manner that has no analog in the accumulation of ice. Blocks of ice may be carried in rivers to the oceans, the ice subsequently melted in warmer latitudes than where it was laid down. The great ice shelves of the Antarctic, where glaciers fill up entire bays, are thought to be susceptible to collapse if the warmer ocean waters erode them from underneath. This would send whole icebergs adrift in the oceans, again exporting the job of melting ice to warmer places.

If all this isn't enough, there is also the problem of land sinking under the weight of mountains of ice, just as Hawaii seems to be sinking under the weight of the lava sent up through its volcanos. Although a slow process, the land sinking could aid ice breakup by lowering the land-glacier interface below sea level, promoting the undercutting of glaciers by runoff in warmer times and transforming the coastal land glaciers into a more vulnerable ice shelf. No one really knows how fast land sinks, but it does rebound once the weight is removed, and a part of Scandinavia covered by the glaciers of the last ice age is still rising, by about one story every 300 years.

IF SUMMERS BECOME HOTTER, even though winters simultaneously become equally colder, it won't average out because of that asymmetry in buildup and meltdown. There are several astronomical mechanisms that indeed produce such exaggerated summers. About half a century after James Croll analyzed our planet's orbital eccentricity, a Serbian mathematician was languishing in a jail during World War I, a prisoner-of-war held by the Austro-Hungarian Empire. He probably kept himself busy calculating the orbits of the planets, for in 1920, shortly after he was released from jail, Milutin Milankovitch published his calculations on the earth's orbit, showing how it had changed over many hundred of thousands of years due to the attractions of the other planets.

Not only does the eccentricity of the earth's orbit change, but so does the season in which the earth makes its closest approach to the sun (called perihelion). Currently we are closest to the sun on January 2 and about 3 percent farther away in July -- which reduces our sunlight by about 7 percent. But the date of perihelion changes, getting later every year as the spinning earth precesses like a spinning top wandering around the floor (astronomers call this change in the season of perihelion the "precession of the equinoxes"). About 11,000 years ago, we were closest to the sun in June. The date of perihelion drifts later and later in the year; it takes anywhere from 13,000 to 25,000 years to complete a circuit. An average cycle is something like 22,000 years (actually, it is typically a combination of a 19,000- and a 23,700-year rhythm, giving different results each time around). When our closest approach is in June, we have hotter summers and colder winters in the northern hemisphere. Of course, it's vice versa in the southern hemisphere, but -- another asymmetry -- down south they don't have as much land mass at higher latitudes on which to house glaciers. Just look at a globe: in the southern half, there is little land between 50 and 70 degrees latitude, as compared to Alaska, Canada, southern Greenland, northern Europe, and the vast expanse of Siberia in the corresponding northern latitudes.

A change in the tilt of the earth's axis changes, over a cycle about 41,000 years long, exerts a second effect on the seasonal distribution of the yearly energy from the sun. At minimum tilt (22°), the sun comes about as far north of the equator as Isla de Pinos, off the south coast of Cuba. It currently makes it to 23.4°, just north of Havana. But at maximum, it stands overhead at noon in Key West, Florida (24.5°). This 2.5° difference in latitude is the same as that between New York City and Washington, D.C., between Edinburgh and Manchester, between Geneva and the Riviera. Such a 2.5° difference may not make much difference in Florida, but it amounts (because of the cosine of the angle changing more steeply) to a 10 percent difference in the noontime sunlight that reaches middle latitudes. The wobble cycle seems to repeat every 41,000 years, but it is again a complicated oscillation, involving major components from 39,700 years up to 53,600 years. When the tilt is maximum, the northern latitudes get a lot more sunlight than otherwise.

Because the advance of perihelion has a different cycle period than that of tilt, these two influences on summer heating in the northern latitudes are often out of phase (as they are now). But when the closest approach to the sun comes in early summer, and the tilt of the North Pole toward the sun is also near maximal, the conditions are optimal for melting glaciers: the daily sunlight reaching the North Pole in June is 28 percent greater than when conditions are worst for June sunlight there. This peak in June sunlight occurred 11,000 years ago, and 127,000 years ago, and 210,000 years ago, and 335,000 years back. This near-coincidence in the two rhythms might be called the "tilt-perihelion beat". It is this particularly successful melting of glaciers during hot summers at northern latitudes that may set the major ice age rhythm, not so much the sunlight during the rest of the climate cycle.

All of these rhythms can be seen in the climatic records of ice obtained from sea-floor samples in which a long vertical core of sediment is taken for analysis. While most of the oxygen in water is the common isotope of oxygen that has an atomic weight of 16, about 0.2 percent has two extra neutrons, and H2O made with it doesn't evaporate as well from the ocean surface. The ice is therefore built up preferentially with oxygen-16; the percentage of the heavier oxygen-18 in the ocean climbs slightly as the lighter isotope evaporates more than it returns via rainfall. By analyzing the ratio of the two isotopes in sea floor limestone, one can see that it changes over the millennia, reflecting ice building up and then melting. The sea-floor cores give much better evidence of the ice-age rhythms than does evidence from the land, since the evidence of one glaciation may be rearranged and ground up by the advance of the next one. Based on moraines and such, it was once said that there were only four ice ages, all in the last 800,000 years; now we know that there were several dozen spanning the last 3 million years.

The rhythms seen in the sea floor are complex, multiple frequencies adding just as in the sound produced by a string quartet, but again there are identifiable components. The longest component identified is of about 413,000 years duration, identical to the major component of the eccentricity change in the earth's elliptical orbit. The 105,000-year component in the cores matches up well with the other components of the eccentricity rhythm. The core shows that ice also fluctuates with a 41,000-year period, which matches up with the period of the earth's tilt change. Likewise, there are core rhythms of 24,000- and 19,500-years duration, matching the two major components of the precessional period. There is even a minor 60,000-year rhythm in the cores that the Belgian astronomer André Berger predicted from an interaction of tilt and precession, and which Milankovitch missed. Everything contributes to the ice rhythms, but the switchover from accumulation to net melting may be the key factor because the melting goes faster than the accumulation.

TAPESTRIES OF LAVA adorn the right bank -- billboard-sized walls composed of many vertical columns, the crystalline form that viscous lava takes when it quickly cools in place. The tall columns have six flat sides, and are formed via the cracks that develop as the lava shrinks during cooling. The packing principle strikes again: the array indeed looks like a fractured honeycomb, hexagons and all. Here and there a tall hexagonal column will be broken, the top remaining like a stalagmite, the exposed end being about the diameter of a bailer bucket. All together, it seems like a giant version of asbestos, the sun glistening on the polished dark bronze surfaces where the river has been at work.

The relief makes the honeycombs look like works of modern sculpture that might cover a whole wall of an art gallery. Someone ought to come down here and do some silicon impressions of them, make molds and cast bronze copies. That seems compatible with the spirit of the Park Service's nice rule for visitors: Leave only footprints, take only pictures. But don't step on the cryptogams!

One of the lava flows extends well below river level, we learn as Rosalie reads aloud from the geology guidebook. One wall shows that the river channel was once filled with lava, which caused the river to find a new path. This new channel was also partly filled with lava, though the river managed to cut through much of it. All this, one reads in the rocks. If one has a practiced eye.

Carried away, perhaps, by His matchless creation, the Garden of Eden, He forgot to mention that all He was giving us was an interglacial.
......the playwright ROBERT ARDREY, 1976

GIVEN ALL THE CLOSE MATCHES, it seems clear that changes in the earth's orbit and spin axis drive the ice ages, though one still has to explain exactly how the accumulation and melting periods work. One model postulates that melting operates four times faster in warming climates than accumulation does in cooling climates; a melting rate of 63 percent in 10,600 years gives a close match to all the climate fluctuations in the last 100,000 years when driven by the precessional and tilt rhythms of the same period.

The last time that the climate was this warm was around 128,000 years back -- and that warm "interglacial" lasted only 15,000 years before it had retreated halfway back to the glacial peak ice accumulation. Using the astronomical cycles and ice age models, one may predict that a similar half-back period may be only 3000 years in the future, though the peak glacial period is not predicted for another 114,000 years. We are probably 75 percent through our period of less-than-average ice. Indeed, there is a 5,000-year jitter -- the ice sheets could have started anytime in the last 2,000 years, but haven't. Yet.

Of course all bets are off, because of the changes that our civilization has made in the atmosphere and in the plants during the last century. We may have to worry first about further melting from greenhouse-type warming, switching us out of the accumulation mode into the much faster melt mode.

Some people say, coastal cities aside, that a warmer global climate might be good for agricultural productivity because of both the warmth itself and the more CO2 there would be in the atmosphere as raw material for the plants. It would, however, be a disaster for western states, let alone the river-runners: 2°C. of warming is predicted to reduce Colorado River runoff by 40 percent, the Rio Grande's by 75 percent. People conveniently forget that our best example of a warmer climate, the period about 8,000 to 4,000 years ago when even the Sahara Desert was growing grass and trees (this "climatic maximum" was due to tilt and perihelion effects peaking 11,000 years ago), also produced climate changes that created dust-bowl conditions and dried up the humid "corn belt" of North America (much of whose moisture comes up from the Gulf of Mexico). And while the Sahara, Arabia, and western Australia might temporarily get more rainfall for crops than would be lost in the American Midwest, the soils are poor in the subtropics; they are nothing like the superb soils of Europe and North America. Given that the American Midwest now feeds much more of the world than just North America, warming could cause mass starvation.

And paradoxical freezes often happen during melts, it would seem. For example, a sudden melt can dilute the salinity of the oceans, thus raising the freezing point of seawater. Easier freezing would cause the winter pack ice in the arctic latitudes to extend much farther south, its white surface reflecting light back into space that would otherwise be absorbed, and thus generally cooling things back down for a while. That's a lot of cold, just from a little warming. Five such quick reversals in a warming trend may have happened during the last ice age, brief cold periods taking hold within a century and usually aborted within a few more centuries (though one lasted 10,000 years).

It's not just paradoxical cold that would plague us during warming but also coastal flooding and the inundation of low islands. With only several stories rise, Florida would be largely underwater. About 11,600 years ago, during the melting of the great North American ice sheet, part of that glacier may have surged forward into central Wisconsin due to all that lubrication beneath it. Then, so the interpretation goes, so much water poured down the Mississippi River that sea level rapidly rose. This date, it has been noted, corresponds to the date given by Plato's ancestor Solon, who said that Egyptian priests had told him that the deluge which destroyed Atlantis was 9,000 years before their time, putting it at about 11,500 years ago.

Whether the Wisconsin ice was responsible for a deluge or not, such nasty things can happen as ice sheets retreat. This is a matter which we worry about, because the greenhouse gases we release into the atmosphere might eventually warm things up enough to start Greenland and Antarctica melting. The usual concern is about "fossil" CO2 from burning coal and oil -- it's atmospheric concentration has gone up 40 percent in the last hundred years. But there's also the refrigerator and spray-can gases; nitrous oxide from fertilizers; even such prosaic stuff as the smelly methane released as intestinal gases by humans and all the human-bred grazing animals (methane is increasing about one percent per year).

Since the last ice age melted off, agriculture has been remaking the face of the earth, allowing the hunter-gatherer population to expand a thousand-fold. Now we are busily engaged in insulting the earth in every possible way, cutting down the rain forests, polluting the oceans, burning up the fossil carbon deposited over hundreds of millions of years as coal and oil, acidifying the lakes downwind -- and all in only a matter of a century or two. We should not expect the earth to be able to buffer these changes; the ecosystems just haven't experienced such insults in the past, there hasn't been time for resilient ecosystems to evolve.

To keep every wheel and cog is the first precaution of intelligent tinkering. {R3} The ecologist ALDO LEOPOLD, The Sand County Almanac, 1949.

Mile 188
Whitmore Wash
Twelfth Campsite

NO ONE HAS GONE HIKING. Unpleasant traces of civilization, such as the jeep trail up at the top of the cliff behind us, are too near at hand. Such as the hose hanging down a nearby cliff, once used to bring gasoline down to the river. Incredibly, the Park Service in 1960 permitted powerboats with giant engines to attempt to run upriver from Lake Mead as a stunt ("Jet-powered boats conquer the big rapids!", screamed the headlines). And they refueled here. Desert recovers slowly from insults. We instead go visit the Whitmore Wash art gallery.

No lava tapestries here, but up behind the sand dunes on the right bank is a flat rock face of sandstone about the size of two large outdoor billboards. Even from the river one can see that red symbols have been painted on it. There is an overhang that seems to have protected them from the weather for the millennium.

Upon closer inspection we see that they are reddish pictographs of typical Anasazi design. Some are high enough up that one wonders if the Anasazi used stepladders to reach them. The alternative, I suppose, is that ancient visitors eroded away the sandstone ledge in front of the rock face over the centuries, lowering the floor; this sandstone does easily revert to sand, I notice as an edge of the path crumbled away beneath my left foot. The trail climbs a little, and even more pictographs come into view. This must have been a very popular place. And the caves which form under some of the sandstone layers near the base of the trail look as if they would have made good places to live. Major Powell saw some wooden Paiute dwellings down here, but no trace of them remains.

There is seldom any realistic depiction in Anasazi pictographs, "modern art" having displaced realism even earlier than I'd thought. Except for some obvious sun symbols and a hand outlined by blown paint, one usually has trouble guessing what the pictographs are all about. Anasazi pictographs are more like modern trademarks and logos than like today's international information signs. Some may, like the pictographs we saw at the Hopi salt mines, simply be clan symbols. Pre-Columbian art in the Americas isn't big on the realistic depictions sometimes seen in the cave art that flourished at the height of the last ice age in Europe. Starting about 27,000 years ago, French and Spanish caves were decorated with hunting scenes, probably creating grottos in which young hunters were initiated into the mysteries of the big game hunts by the light of oil lamps.

Why did art start so late? Since modern-type Homo sapiens has been found in South Africa from as long as 100,000 years ago, our displacement of the Neanderthal type in Europe, between 41,000 and 33,000 years ago, hardly seems to herald the beginnings of a new, artistic human species.

Though man is originally tropical in his origins, the ice has played a great role in his unwritten history. At times it has constricted his movements, affecting the genetic selection that has created him. Again, ice has established conditions in which man has had to exert all his ingenuity in order to survive. By contrast, there have been other times when the ice has withdrawn farther than today and then, like a kind of sleepy dragon, has crept forth to harry man once more. For something like a million years this strange and alternating contest has continued between man and the ice.
......LOREN EISELEY, 1972.

THE ADVANCE AND RETREAT of the glaciers surely affected our ancestors. Wherever they lived, the climate was probably altered in some measure; even the hominids in Africa could have seen glaciers on some of the tall mountains such as Mount Kilimanjaro (both it and even Hawaii's Mauna Loa had glaciers during the last ice age).

For the hominids trying to live in the temperate zones (dry as it is, South Africa today has plenty of hailstorms, and snow may be seen even in midsummer), it would have been a choice of either retreating from the advancing glaciers or just moving to the tropics. Migration is a sensible solution to winter, adopted by many animals. But it depends on there being enough to eat when one arrives at the warmer location. If others of the species live there year-round and have expanded their population numbers to fully occupy the niche, there will be a lot of resistance to fair-weather migrants. And this winter rule surely applies as well to ice-age changes in climate. Either the population will shrink, or the frontier inhabitants will just have to learn to cope with the ice age. The Grand Canyon Anasazi probably faced the same problem when the droughts forced them out: the good land elsewhere was already taken.

And so the boom of population in interglacial times will create some incentives for those in temperate climates to stay put and adapt to the situation as the climate worsens. They'd have had to live at low density, much as the Inuits do today in the Arctic. To get through the winters, they'd have had to either learn to eat grass or an animal that did; living on a coastline gives some additional opportunities, such as eating fish or fish-eating seals and bears. Food storage is a fine idea, but it conflicts with the need to move around easily which hunting marginal areas tends to involve, as one depletes the game (or the animals get wise to the hunters' tactics).

Hominids that were forced to hunt would have been edited by natural selection for those with better brains for hunting. Not all hunting involves throwing, but surely throwing skills were under considerable selection pressure at some point, as witness our skills compared to those of chimps and gorillas. Those who interbred with the more tropical population wouldn't tend to retain those features very well, because of the dilution. Those tribes that were more isolated and inbred would tend to keep more of their hunting adaptations. Yet there are lots of hazards to inbreeding (reduced efficiency of the immune system, for example), not to mention the possibility of a small tribe being completely wiped out by a chance turn of events. The anthropologists suggest that a minimum tribe of 500 individuals is needed, probably composed of twenty bands of five families each, just in order for there to be a likely marriage partner available when an individual reaches the customary age.

Very similar arguments can, however, be made for many species, especially omnivores. Why us? Why not other apes? Why not bears? What did we do differently so that such conditions selected for bigger brains? One answer, of course, is that perhaps that the ice ages did affect other apes, but they didn't survive or conveniently fossilize where they could be found. When one is talking about a singular case, everything that happened along the way seems essential. That's why fast-track arguments are so important when sifting through probable brain-ballooning factors.

Throwing is a fast track, perhaps the fastest one. It is a skill important on the fringes, where natural selection is most severe, the dilution opportunities most restricted, and speciation most probable. It is crucial every year during the winter, when the alternatives to meat are poor. The regular improvement in the climate after each ice age would have led to a gradual population boom on the frontier -- but not necessarily in the tropics, already pretty fully occupied. If the brain machinery for throwing is also useful for scenario-making and thus consciousness/cleverness/language, it might have led to frontier hominids that could occasionally displace the tropical population as advancing ice drove them south, even if throwing per se wasn't required to make a living there. Squeeze the center, but later expand the periphery. This ratchet for hunting ability would have been cranked another notch every now and then, thanks to the regular constriction and expansion of the frontier population by the ice ages.

per aspera ad astra
("through difficulties, to the stars")

ARE HUMANS STILL EVOLVING? The inevitable question comes up late in the evening. Darwinian gradualism did lead to the notion that evolution is always in progress, gradually changing us into something "better." The Colorado River Staircase (or, if you prefer, the punctuated equilibrium) view says that species don't change very much once they're established. Even though we interact with our environment and some fools falter, the large size of the human gene pool means that it is pretty hard to overcome the Law of Large Numbers. We're basically overqualified, at least in the environments in which most of the human population lives today, dying early more by chance and disease and old age than from lack of relevant skills possessed by their neighbors. Even if the people living on the fringes, such as the Arctic Circle Inuits and the Kalahari San, were to be shaped by natural selection to have some inborn skills twice as good as other groups, the interbreeding possibilities are likely to dilute these skills. Travel being what it is today, the gene pool is getting stirred as never before. Natural selection doesn't do much to humans these days; while affecting individuals, the mean character of the human species probably doesn't change. It probably hasn't since agriculture began.

Even if one of the traditional catastrophes were to happen (a meteor, volcano, or ice age), the sheer size of the human population makes it unlikely that much of a change would occur. If it did, it would be because of a fluke in the genome that created reproductive isolation for a small group under severe selection pressure. So forget about traditional natural selection when thinking about the human future; certainly, one cannot get any support from science for the notion that we shouldn't subsidize the unfortunate.

Besides, human evolution has been on a suprabiological track -- called cultural evolution -- for a long time. It's far faster than biological evolution, with a different set of rules. Consciousness, in combination with such cultural developments as writing and science, produces innovations almost unthinkable for biology. Cooperation, initially established by biology in ways seemingly counter to the popular conception of "competitive" Darwinism, has led to such cultural innovations as community child-care and banking. Plus other collectives such as insurance companies, who take advantage of the Law of Large Numbers.

And we might also develop superhumans without actually causing speciation, merely by increasing the variability on the high end of the skills scale, so that there were more geniuses around than formerly. Just as genius currently winks on and off in the population, it might be quite random in nature, with bright parents being no guarantee of bright offspring. The most probable way, by far, to create more of these extraordinary people would be through education. Genius is basically a brain whose parts happen to work together extraordinarily well (not through any "genius gene" but through a particularly effective combination of many genes), and we might find some better ways of training for that kind of fine-tuning, rather than leaving it to the hit-or-miss of our present malnourished educational system.

Yet with all that said, human biological evolution may not be at an end. There are ways.

But it's late. There's a half-moon rising over the Canyon walls as we finally get up and head off to bed. Looking up at the Big Dipper, I estimate that it's after midnight. I've learned to use the pointer stars as a clock (the last two stars of the Big Dipper are in line with the North Star). In early summer, the pointer rotates around the North Star from about ten o'clock down to about six o'clock between dusk and dawn. I usually lay out my sleeping bag to face north so that I can easily check the time if I wake up in the middle of the night.

...Skinner wrote that "the contingencies responsible for unlearned behavior acted long ago" as though evolution of the mechanisms for generating endogenous behavior is somehow over, genetically set for ever, so that only ontogenic variants are now relevant. I submit that in every organism, including man, there are constant gene mutations affecting neurons, circuits, modulators, transmitters, and ion channels which result in genetically determined behavioral variation. Natural selection is acting on the resulting variants in behavior right now. The genetic changes may do no more than alter the time dependencies of a single ion channel, but they could change the world.
......the neurobiologist GRAHAM HOYLE (1923-1985).

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