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William H. Calvin
This page is at http://WilliamCalvin.com/bk3/bk3day9.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).


Mile 134
Tapeats Creek

ALREADY IT'S A BIG DAY FOR BIGHORNS. Jeremy DuBois woke up this morning and was looking sleepy-eyed out of his tent, studying the boulder-strewn hillside across the river with approximately the attention one gives the back of a box of breakfast cereal. Then he thought that he saw a boulder move. Soon the binoculars were out and everyone was standing down at the edge of the river trying to count bighorn sheep. Three was about all that I spotted. But Fritz says that she once had some passengers who were experienced hunters, and that those guys could point out ten bighorns on a hillside where everyone else had only seen three. The Anasazi also probably had well-developed bighorn schemata. One of the tricks, of course, is to watch for slight movement. But the bighorns really do look like boulders otherwise.

There were tracks around the kitchen this morning when Fritz went to start breakfast, though no one saw the ringtail. They're not really cats but a relative of the racoon, with a cat-like body and fox-like face. The boatmen say that sometimes they see ringtail tracks around the kitchen almost every morning of an entire trip, demonstrating that there are plenty of them throughout the river corridor (or that they had a stowaway!). They're seldom seen because they're thoroughly nocturnal, spending their days up on a ledge or in a rock pile. They're quite agile and also bold animals; scientists studying rodents in the bottom of the Grand Canyon have had ringtails march into their tents during the night and make off with their specimen collections. Fritz says they spotted a ringtail one night who, having extracted the squeeze container for honey from a kitchen box which wasn't properly fastened, was having a feast. The ringtail ignored all the people that had gathered with flashlights, and calmly continued eating the honey. It remained long enough for them to count the rings in its long, bushy tail: ringtails sometimes have as many as sixteen black bands. Though the local ringtails probably eat mostly rodents and lizards, they also like rabbits, insects, snakes and fruit. And honey.

We're only going about three miles today, at least by river; we'll probably hike more than that. We shall go down to Mile 136 and explore Deer Creek all day, then take ourselves down to Overhang Camp at Mile 137. At breakfast, there were a group of people who hadn't seen Thunder River yesterday afternoon and who suggested a loop hike through Surprise Valley to Deer Creek, meeting up with the rest of us there in the afternoon. They'll have to do without a boatman for a guide, however; though several passengers have volunteered to row the short distance, there are three rapids between here and there, one with a big back-eddy known as "Helicopter Eddy." The river is at its narrowest and deepest here, making the currents tricky.

Alan gives the hikers some advice: don't drink the water, as the surface water may come down from some campgrounds up above us on the North Rim. And he advises all of us to watch out for the poison ivy on the trail somewhat above the river, going up around the lower falls at Deer Creek. Poison ivy is a problem in only two places, back at Vasey's Paradise and in that one small patch near Deer Creek Falls. The Canyon is amazingly free of stinging and itching hazards at most places and at most times of the year, just so long as one avoids the red ants in the daytime and shakes one's boots out in the morning in case a scorpion took up residence during the night. Even the Canyon rattlesnake is a sluggish coward.

DARWINIAN GRADUALISM is one way to get a new kind of animal, such as a Ringtail. As Darwin thought through the consequences of natural selection editing the variations within a species, he saw that there should be a drift toward those variants that were more successful in coping with their environment. Thus, he said, there would be a gradual shift in the characteristics of a species. It was perfectly good reasoning based on the data of 1858, before the days of the gene concept or the data from population studies. Darwin thought that nature was pretty well filled up with species, and that the evolving species would likely have to drive a wedge between existing species, taking over some of their niche (as we would now say). Darwin's metaphor of the wedge has dominated our thinking about evolving species.

But now it seems as if whole populations may not gradually shift their characteristics in such a conveniently gradual manner. The fossil record of marine invertebrates tends to show a species not changing at all (except, perhaps, for a slight increase in size) for a very long time. Then, without warning, it is likely to disappear, replaced by another similar species -- which itself lasts for a long time without change. This is like the "model year" of American automobiles, where change occurs only once a year (it's just that the snail's model year lasts 10 million years). Variations may still occur within the model year (particularly, it is reported, in the cars that go down the assembly line on a Monday!), but they cause little steady drift in the overall character of the species.

Gradual change can, of course, be seen -- Darwin was quite familiar with what animal breeders accomplished. The difference may well be in the size of a population: small subpopulations may be able to evolve gradually and rapidly; large populations with well-stirred gene pools may buffer much change and slow down the pace of gradualism so much that it becomes insignificant.

And so the events observed in the fossil record may simply be those of the large central population. Small subpopulations, off in a corner isolated from the rest, may evolve gradually and rapidly, as if -- in my thunderstorm-spawned metaphor -- on a spiral ramp off in one corner of the parking garage. Their adaptations might suit them to a new niche, eating a food that no other animal had been able to exploit. Or the adaptations might merely make them more efficient at earning its living in the same way exploited by their parent species.

If the subpopulation returned to mix with the parent species after attaining reproductive isolation, it would take a long time to displace the parent species by outcompeting it on equal terms. Mass extinctions would, however, offer a special opportunity to an improved species, when every bit of efficiency would count in the crunch of hard times. And hard times occur at least every 28 million years or so. It may be that several of the branches on the line to humans were affected by the mass extinctions. The apes split off from the Old World monkeys about 34 million years ago, not long after the "terminal event" of the Eocene, an unusual climate change that affected winter temperatures but not summer temperatures in the temperate zone's forests. The winters, judging from the botany, were about 20°C. colder than usual. In the seas, the protozoans called Radiolaria were almost decimated. And at the very same layers in sea-core samples of the radiolarian ooze in which the numbers of protozoan drop, geologists find tektites. These are little rounded pieces of glass, most of them smaller than the tip of a finger. This glass is particularly homogeneous, nonporous, water-free -- all quite unlike volcanic glasses, and so it is suspected that tektites were made in space. Their distribution supports the idea of a meteor breaking up in the atmosphere: though the area in which they are found is called the "North American" strewn field, it is extends from the Caribbean west through the central Pacific to the Indian Ocean.

Now how might such a meteor impact have caused a climatic change? Microtektites, or the dust kicked up on impact, in the lower atmosphere would be washed out by rainfall in a matter of weeks. In the stratosphere, it might take a few years. But the evidence for climatic change lasts 1 to 2 million years. That suggests that if something remained to shadow the Earth, it remained out in space, orbiting the Earth, unaffected by the atmosphere. But how could that produce this funny business of normal summers but extra-frigid winters in the temperate zones? In 1980, John O'Keefe suggested a clever model for a Saturn-like ring around the Earth, composed of the tektites and microtektites that were pulled into orbit by the Earth's gravity.

Rings tend to form around the equator because of collisions which dampen the north-south component of the velocity; the gravitational pull on an orbiting particle is not uniform because of the flattened-at-the-poles shape of the Earth, that equatorial bulge associated with a non-too-rigid spinning body. And so, after a year or two, what started out as a widely distributed orbiting cloud would become concentrated in a narrow ring around the equator. Now when the sun is overhead at the equator on March 21 and September 23, the shadow cast by such a doughnut will simply be a narrow ring around the equator. But when the Northern Hemisphere is tilted 23° away from the orbital plane of the Earth at the winter solstice, the ring will cast a broad shadow on the northern temperate and arctic zones. At the equinoxes, it would not matter how far the ring extended out into space, since the sun's light would be arriving edge-on; at other times, however, the depth of the ring would determine how broad a shadow was cast. O'Keefe simply assumed that the inner radius started 3200 kilometers above the surface and extended for another 6400 kilometers (an earth radius) out into space. This would block about 75 percent of the sunlight at the solstice, about enough to cause the 20°C. temperature drop. In the summer, the sunlight would come in above the ring, so there would be no shadow in the northern hemisphere (though, of course, the southern hemisphere would be shadowed then). Thus, there would be cold winters but normal summers.

And the extinction associated with this event might have given the apes their big chance by vacating niches. Their split from the Old World monkeys has been dated to about 34 million years ago using DNA differences and the characteristic rate at which they occur. An early fossil ape called Aegyptopithecus is at least 30 million years old. The DNA date for gibbons splitting off is about 22 million years ago. There were a number of subsequent splits, since we have fossil apes like Proconsul between 22 and 16 million years ago in the early Miocene, Sivapithecus at 17 million years ago, and the related Ramapithecus at various younger dates. The ancestor of the modern orangutan Pongo seems to have split off at about 16 million years ago, judging from the accumulated DNA differences, and indeed a Sivapithecus skull looks surprisingly like an adult orang, with its huge round eye sockets and long shelf-like snout sticking out in front.

But there were two hominoid splits about 10 to 11 million years ago: the common gibbon split off from what became the siamang, and gorillas split off from the line that went on to become chimps and humans. This date is about when the mid-Miocene extinction occurred, the most recent of the 28-million-year series of clustered extinctions and meteor craters. So, someone joked, maybe the last visitation of the comets gave us an opening, and kept us from remaining gorillas.

Mile 136
Deer Creek Falls

THUNDER IS HEARD from the Lower Deer Creek Falls as we approach it, walking up the beach. It is a tremendous volume of water, falling about ten stories without a break, in one narrow column. The spray rising from the pool has force too, as several people discover when they attempt to wade toward the falls: the spray blows them back, Jackie sitting down in the pool as a result -- literally blown off her feet. Standing under that force of falling water would be like walking into the stream of a fire hose. But it is a beautiful sight, this waterfall and its pool, tucked into an alcove of rock and greenery.

Deer Creek at Mile 136, from Leonard Thurman's Grand Canyon River Running web pages.

But we do not stay long, as we are starting off on a hike up above the falls into the valley beyond. We have been hearing all sorts of things about the valley and the fossils to be found there at the entrance to the labyrinth that leads to the lower falls. The trail starts downriver of the falls, and we have a lot of climbing to do, not just the ten stories of the lower falls, but that of the upper falls and the cataracts as well.

As we gain elevation on the steep trail, views up and down the Canyon open up. We see the narrows produced by the Surprise Valley landslide, and marvel at the size of it. This doesn't look at all like a landslide because the whole block slid sideways. Then the trail turns in and the view narrows as we approach Deer Creek Canyon itself. The Tapeats forms interdigitating scallops for several blocks in from the river. At the bottom of it, three stories below our trail, thunder the waters of Deer Creek on the way to its plunge toward the river. Our trail is not wide, not for the severely acrophobic. But those who do look down are rewarded by the sight of a redbud tree in its own little alcove. The creek formed a pothole at one time, as stones were swirled around, too heavy to be carried high enough by the rushing waters to escape, gradually wearing themselves down. And gradually forming a deeper pothole via another emergent property. Eventually enough sandy soil gathered in this pot to support a tree. It is miniature, thanks to being root-bound in a pot of fixed size, but it looks as if oriental gardeners tended it every week.

Trail to Deer Creek Canyon from Leonard Thurman's Grand Canyon River Running web pages.

The narrow canyon starts to open up and we see greenery ahead -- and then the spray from the waterfall that moistens them. It is a beautiful waterfall of two stories, falling down one side of a U-shaped ledge at the same level on which we are walking. In several stages, it cascades down to the bottom of the narrow cataract.

The canyon opens out because we have reached the top layer of the Tapeats Sandstone; the Bright Angel Shale that overlies the Tapeats here is more easily eroded, leading to a wider canyon by undercutting in the same manner as the Grand Canyon itself widened from Marble Gorge in Furnace Flats. The falls here are surreal, an impression aided by our seeming inability to get a better view of them by moving around -- just as in a dream where you cannot do what you command, you discover that there is really only one place from which to photograph the falls because of the horseshoe ledge connecting to the serpentine canyon. Move from the right viewpoint and the view disappears.

As one approaches the slippery top of these falls, a whole valley opens up, as if you'd just passed through a tunnel entrance to a secret interior valley. Here we encounter others looking at fossils. So they say. I look carefully for small details. Then someone tells me to step back and look -- and then I see it. The entire slab of rock is completely covered with an intricate pattern of finger-diameter rope work, suitable for a wallpaper design. Except that these are the casts left by big worms burrowing through the mud. Something of the Cambrian equivalent of a dinosaur footprint. And they're all over. I now remember seeing small sections of rock bearing such worm works in a museum on the South Rim -- but the size of this rock slab is not to be believed. It is just lying there next to Deer Creek, not covered by glass or Park Service warnings, probably getting washed off every time that Deer Creek floods. It also exhibits no damage, no graffiti from a hundred years of river-runners.

The creek flows knee-deep through an opening valley, and we wade in the water looking for rocks bearing fossils. I pick up hundreds of small rocks and find several possible fossils, though of what I cannot tell. The creekbed leads to a small rapid, suitable for bathing and frolic.

As I search for shade later, back at the upper canyon entrance, I try lying under an overhanging cliff of Bright Angel Shale. And to my surprise its ceiling is covered with fossil tracks -- the paths of Cambrian worms and, it is said, trilobite tracks. This superb ceiling is larger than many dining tables, an exquisite collection of worm works.

Source of Deer Creek from Leonard Thurman's Grand Canyon River Running web pages.

There is, Alan tells us, more to see further along the trail: the source of Deer Creek cascades out of the canyon wall several miles back up the valley. And there is time. We'll probably meet up with the Surprise Valley hikers back there. Alan, his brother Ken, and his father Gordon, are all going. Temptation. But I decide to stay and explore the lower canyon instead. There are steep paths down into the cataract on the far side and, on the way, nice cool places to sit and admire the beauty. When I emerge from the cataract with the aid of a helping hand from above, I find a group collecting under one of the Tapeats ledges with a view out over the narrow canyon, talking about another kind of ascent.

FROM APE TO LUCY was the topic -- all the problems in getting from a typical mid-Miocene ape, perhaps like the chimp, to an early hominid like Lucy, who walked around upright 3 to 4 million years ago in the Afar triangle of Ethiopia. She had the nice rounded pelvis and the indented knees that go along with walking around upright. But she was clearly only partway from chimp to human in such changes. And her skull was strikingly chimplike in size and shape -- this, near the end of the Australopithecus afarensis line at 3.0 million years ago, at the end of the model year. After that, A. africanus came into style. The artist's reconstructions always show them modestly covered with hair, not naked in the manner of modern humans before the clothing mania. The great cover-up. No one knows if Lucy had ape-like hair, but it certainly was lost somewhere along the line -- and it probably wasn't just when clothing came into style. What on earth could select for hairlessness?

The traditional explanation is that hairlessness is an adaptation for running on the plains. If, so the story goes, our ancestors needed to run down animals or run away from them, they'd overheat without the peculiarly human sweat glands that cool our blood. And sweating works better without hair in the way. If that were true, one would expect other animals to have discovered this alleged physiological principle too -- but the people visiting a zoo are probably to be the only animals sweating. Indeed, no other primate has done anything quite as physiologically stupid as prolific sweating. Baboons are adapted to savannah life, and run around faster than humans just fine with more traditional temperature regulation mechanisms, though humans are better adapted to a really sustained long chase.

And sweating is profligate of both body salts and water; apes conserve water so well that they seldom have to visit waterholes where predators lurk in ambush, seldom have to seek out salt sources. In a hot climate, humans have to drink repeatedly throughout the day (as we are repeatedly reminded by the boatmen); in the hot savannah in pre-waterbag days, this must have caused hominids to stick close to creeks and lakes in a manner atypical of other savannah animals.

Furthermore, hairlessness has a truly serious disadvantage, since primate babies cling to the mother's fur for transport. As hair became scarce, one supposes the number of babies injured by falling would have increased considerably (even in hairy chimps, infant falls are the major cause of mortality). It makes you think that hairlessness must have been important for some other, much more important, reason -- preferably in a situation in which infants falling wasn't an immediate problem. But where wouldn't that be a problem?

There really is such a place: while wading around offshore, catching crabs.

Parts of [the world] are neither land nor sea and so everything is moving from one element to another, wearing uneasily the queer transitional bodies that life adopts in such places. Fish, some of them, come out and breathe air and sit about watching you. Plants take to eating insects, mammals go back to the water and grow elongate like fish, crabs climb trees. Nothing stays put where it began because everything is constantly climbing in, or climbing out, of its unstable environment.
...... LOREN EISELEY, The Night Country, 1971
DID OUR APE ANCESTORS SPECIALIZE IN SHELLFISH? Back in the forties and fifties, Alister Hardy was studying marine mammals, which of course are land animals that have somehow been forced to take up life in the sea and develop aquatic adaptations. He began to realize that humans had a group of peculiar features which, in any other species, would immediately lead one to surmise that they had once been land animals, were forced to become aquatic, and then returned to the savannah, keeping their swimming skills and other aquatic adaptations. Virtually all the hairless mammals today are either aquatics, or wallowers like pigs, or probably descended from such (the exceptions are the naked mole rat and an artificially bred Mexican hairless dog). The longer the animal has been in the water, the more complete the hair loss (seals and beavers are recent converts). As anyone who has tried to swim with clothes on can testify, they're a drag. Competitive swimmers have been known to shave off all body hair before a race.

Oftener than not, mammals who return to the water and stay there long enough, especially in warm climates, lose their hair as a perfectly natural consequence. Wet fur on land is no use to anyone, and fur in the water tends to slow down your swimming. She began to turn into a naked ape for the same reason as the porpoise turned into a naked cetacean, the hippopotamus into a naked ungulate, the walrus into a naked pinniped, and the manatee into a naked sirenian. As her fur began to disappear she felt more and more comfortable in the water, and that is where she spent the Pliocene....
......ELAINE MORGAN, The Descent of Woman, 1972
Hairlessness is only one of those peculiarities of many marine mammals such as dolphins and whales. Another is the subcutaneous fat layer that they use to make up for the lost insulation of hair (which works only on land, via all the air it traps). We, and the naked marine mammals, have a subcutaneous fat layer all over our bodies, quite unlike the apes. It also helps the streamlining for swimming; an angular ape isn't the most likely candidate for an efficient waterfoil.

Human babies are born very plump, an addition of the last months of pregnancy (when they also lose the body hair they had earlier, called lanugo). They look quite unlike the cadaverous chimp infants, whose appearance is comparable only to either very old or very malnourished humans. Is the fat there to adapt human babies for life in the water, to make them buoyant enough (in salt water) and insulated enough so that they can bob around, hanging onto mother's remaining hair, that on her head? Similar scenes can still be seen in the waters of Tierra del Fuego, floating Indian infants hanging onto their mother's long hair as she swims offshore, collecting shellfish.

Then there is the little matter of upright posture: what preceded Lucy's pelvis? Two-legged locomotion is much slower than the four-legged version it must have replaced; baboons can zoom along at remarkable speeds. But mammals in the water often adopt a vertical posture, peering about and observing, communicating with companions, eating the food they have just retrieved from the depths -- all preferably while vertical. When treading water, when diving, and when swimming horizontally, their legs are positioned parallel to their spines, not perpendicularly as in four-legged land animals. And so the marine mammals lose the elongated pelvis characteristic of the four-legged land animals such as chimps and gorillas. And any land animal that wades into the shallows and maintains a horizontal posture gets its nose in the water a lot sooner than one that stands up on its hind legs. Thus, the horizontal wader would be restricted to about one-third of the shallow water foraging area otherwise available. Shoreline foraging in a drying climate would be a likely transition from four-legged walking to full swimming and diving.

Another human peculiarity among the primates is face-to-face copulation: whatever the reason for this reversal of the usual approach, most of the other aquatic mammals have done it too, probably as a result of the pelvic rearrangements associated with upright posture. There is even the little matter of tears: primates don't cry, but some aquatic mammals do. Tearing and sweating reminds one of salt glands, those adaptations of marine animals for getting rid of excess salt from their fishy diets.

To say that humans were once all professional swimmers and divers is, of course, heresy. In 1960, Professor Hardy let himself be persuaded to gave a talk to the British Sub-Aqua Club at Brighton, surely a friendly audience. Outside the conservative groves of academe, which at the time was quite happy with the savannah theory for the ape-to-prehuman transition (they still are), he put forward his aquatic ape hypothesis that had been gestating in his brain for 30 years. That might have been the end of it, but a reporter was present that Friday evening; the Sunday papers were full of the story Hardy put forward, some with distortions as wild as reporting that "Professor Hardy's startling new theory shows man to be descended from a dolphin." A little 100-million-year error, that being about when cetaceans branched off the mammalian tree.

Sir Alister later said, "I hardly dared to go back to Oxford on the Monday." And so he phoned up the New Scientist magazine and asked if it would publish a proper account of his talk, to counteract the embarrassing distortions. And it did. But, alas, he never wrote up a longer academic account for the professors to evaluate, having retired to concentrate on research concerning religious experiences.

The aquatic ape theory has, nonetheless, survived. Elaine Morgan, a former Oxford scholar, has written two books popularizing Hardy's theory, the best-selling The Descent of Woman in 1972 and The Aquatic Ape in 1982; her updates appear in the New Scientist periodically as she locates new evidence in scattered places.

Anthropologists have been hesitant to discuss the aquatic theory, almost as if they were Victorians standing on ceremony, not having been properly introduced. The physiologists keep adding weight to Hardy's theory, however, as they discover more and more about aquatic mammals. There is something called the diving reflex which all successful divers have (even diving frogs), in which the heart rate slows and the blood supply to the skin is reduced at the beginning of the dive. It is evidently an adaptation to prolong the time that can be spent underwater, by reducing the oxygen consumption rate and thus make it possible to dive deeper and collect food longer. Humans have a well-developed diving reflex that halves the heart rate; water splashing on the face helps to trigger this reflex slowing, and so a face mask may prevent it.

Fueling the debate, the physiologists have been finding strange things about how we differ from other land animals in our regulation of salts, sodium chloride in particular. Most land mammals exhibit a salt hunger when their diet doesn't contain enough salt. And they'll stop eating salty foods when they don't need more salt. We humans, however, don't seek out salt even when we are seriously depleted, as before we start getting muscle spasms. This failing is, in fact, a leading cause of death in the world, given the mortality from childhood diarrhea in underdeveloped countries (it's the salt loss that kills), so that our poor regulation of salt was probably counteradaptive during much of hominid evolution too.

But marine animals have a hard time regulating their salt intake because everything they eat is salty; instead, they develop improved mechanisms to get rid of the excess. Kidney mechanisms, of course, but also tears (yes, that's one way to get rid of salt) and sweating. So why do humans exhibit salt regulation more typical of aquatics than land animals? To get rid of excess salt from a diet of fish and shellfish?

Many hominid-like anatomical changes are seen in one primate which did go aquatic, the swamp ape (some would say swamp monkey) Oreopithecus, whose bones were preserved in large numbers because they sank into the mud; one Italian coal seam yielded a virtually complete Oreopithecus skeleton. It has the short broad pelvis like the upright walker, the hominoid elbow modifications, the flattened face, the short canine teeth, the curved finger bones typical of Lucy and the other early hominids (physical anthropologists love nothing better than to talk about whether bones are straight or curved as a clue to function) -- all the things needed to make Oreopithecus a potential hominid ancestor, were it not for its northerly location and disputed membership in the ape club. But it shows what life in the swamp can do to a primate as the sea rises and the islands become smaller and smaller. It also shows the likely fate of such experiments: Oreopithecus went extinct. One wonders how many other times this process has begun, only for the physical conditions to eventually change faster than the biological capacity to adapt.

One of the first proposals that humans arose from simpler animals also had an aquatic theme. The Greek philosopher Anaximander of Miletus pointed out 2,500 years ago that human infants are far more helpless than the young of other animals and require much more prolonged suckling: if they were originally as helpless as they are now, he maintained, humankind could have never survived. Therefore, Anaximander reasoned, humans must have originated as animals better able to take care of themselves when young. Anaximander thought this human predecessor was some sort of aquatic animal; his proposal, of a slow transformation from these "fish-men" into "land-men", represents a landmark in the history of evolutionary thought.

The objections to the aquatic hypothesis have varied. True, primates typically have a fear of falling into the water -- but various water-loving primates have evolved nonetheless. Besides the extinct Oreopithecus, there are such present-day examples as the talapoin in the rivers of Gabon, the proboscis monkey of the mangrove swamps of Borneo, which sometimes swims well out to sea for unknown reasons, and the crab-eating macaque of the Philippines. Gorillas in zoos are reported to love swimming, especially the breast stroke. An ethologist studying wild chimps at several different African sites now reports that they have no fear of water. Wild pygmy chimps have been seen wading in streams and snatching at fish. So much for that objection.

Anthropologists are forever noting that we have just as many hair follicles as chimps, that our nakedness is merely an illusion. So what? As Elaine Morgan points out, Queen Victoria's face had no fewer hair follicles than Charles Darwin's, but Darwin would have been surprised to learn that his beard was an illusion. It's how thick and fast that hair grows that's the relevant factor, not the anatomical presence or absence of the factory. Such is their addiction to "hard" evidence that anthropologists are forever suggesting that the discussion should be postponed until such a day as there is incontrovertible fossil evidence for the aquatic ape. While seeming to strike a sober note of scientific caution, this tacitly assumes that fossil evidence is somehow the only evidence worth anything, that comparative physiological and behavioral clues to our origins are not worthy of consideration.

I imagine him wading, at first perhaps still crouching, almost on all fours, groping around in the water, digging for shell fish, but gradually becoming more adept at swimming. Then, in time, I see him becoming more and more of an aquatic animal going further out from shore; I see him diving for shell fish, prising out worms, burrowing crabs and bivalves from the sands at the bottom of shallow seas, and breaking open sea-urchins, and then, with increasing skill, catching fish with his hands.
......the physiologist ALISTER HARDY, 1960

SINCE EVOLUTION WORKS FASTEST when animals are isolated in small populations under demanding climatic conditions, evolutionary biology must also become part of the debate. Whether proponent of savannah or shoreline or whatever, one must consider the suitability of the setting in which the ape-to-prehuman evolution is proposed to have taken place: how rapidly can change occur there?. An ideal spot would be an African area which, in the late Miocene, perhaps 7 to 8 million years ago, was forested; had apes; and was then isolated from the rest of Africa, with the advantages of islands for speciation and selection. It would help if said island was later reconnected to Africa in such a way that the East African rift valley became populated with Australopithecus afarensis by 4 million years ago. For this, one must consult the evidence about ancient sea levels, geological events, and climate.

Such an ideal spot on the Red Sea coastline has been identified by Leon LaLumiere, Jr., and it fits very well with the aquatic-ape hypothesis, not with the savannah theory. It is just north of the Hadar region where Lucy and family were found, in the tip of the Afar triangle. Just north of Djibouti, just south of the present Dahlak Archipelago, this coastline is part of the Eritrea provence of Ethiopia, a region of chronic political unrest often unsafe for, and forbidden to, travelers. Alas. The geologists call it the Danakil Alps; about 75 kilometers wide, it forms 540 kilometers of the African coast approaching the Straits of Bab al Mandab, just before the Red Sea opens out into the Gulf of Aden and the Indian Ocean.

Back about the beginning of the Miocene, say 20 million years ago, Africa and Arabia were one tectonic plate. This tectonic plate collided with the Eurasian plate, buckling up the area around the present Red Sea, which then downfaulted. Together with a little sea-floor spreading that got started, this formed the proto-Red Sea, and it connected with the proto-Mediterranean, not the Indian Ocean (which had just witnessed the Indian "continent" crash into Asia, raise up the Himalayas, and become a "subcontinent").

A rift started to form the Gulf of Aden (what separates the Somali Republic on the horn of Africa from South Yemen on the Arabian peninsula, that feature seen from space which looks like a giant can opener had been used on the real estate), but it didn't connect with the Red Sea for a long time. Instead there remained a forested land bridge between forested Africa and forested Arabia (in those Miocene days, the moist tropics extended into southern Eurasia), and starting about 17 million years ago it was used as a migration route by numerous species of African land animals who expanded into Asia during the Miocene. This probably includes Ramapithecus, whose remains have been found from Hungary to China, as well as in Kenya. No one has yet explored the Arabian peninsula for hominoid fossils on the Asian side of the land bridge, though the anthropologists are working their way north along the African rift valley toward the ex-land-bridge, in between civil wars in Ethiopia.

The collision, rebound, and further collisions between Africa and Arabia were accompanied by changes in Africa itself which were far-reaching in their implications. Before all this started, there were a few volcanos and no highlands of Ethiopia and Kenya. Africa, however, began to be torn apart, a process that continues today. By 15 million years ago, two large blisters had formed in Kenya and Ethiopia where lava upwelled and domed up the land surface by a thousand meters or more to form the highlands (a process perhaps not unlike the uplift of the Colorado Plateau, which has volcanos all around its edges). The crust cracked in numerous places, fault lines opening up all over the place, but especially in a north-south direction: a long valley began to be formed. The Great Rift Valley of East Africa today runs from the east coast of South Africa north through the Afar triangle, but the spreading continues up the Red Sea though the Dead Sea and Sea of Galilee to Syria. The associated earthquakes shook down the walls of Jericho numerous times (still, Joshua must have had a superb sense of timing). The Great Syrian-East African Rift is still splitting apart, currently at the rate of 1 millimeter each year (this is, however, ten times slower than Europe and North America are being pushed apart by sea-floor spreading).

With all this, of course, came African volcanos even larger than the present-day Mount Kilimanjaro. As the Ethiopian and Kenyan highlands got tall enough to precipitate rainfall, they caused a rain shadow to the east, the tropical rain forests there began to dry up, and the land was transformed into the patchwork of woodland and open terrain called savannah. The primates that lived there either adapted to the foods and predators of the savannah, in the manner of the baboons, or retreated into enclaves in the manner of the mountain gorilla in locations where their old rain-forest habits were still sufficient to make a living. (There's a price for this: only 240 mountain gorillas remain, pushed up into an "island" formed of wet mountaintops -- a fate not unlike what happened to Oreopithecus surrounded by water.) Just as they had done many times over the ages, plate tectonics and sea-floor spreading were again causing major evolutionary changes to accumulate.

In the late Miocene, the Red Sea was still a gulf of the Mediterranean. But the Med was undergoing a series of dramatic events itself: it dried up into a series of salty lakes. And then refilled. And repeated this cycle 11 to 14 times, probably causing all sorts of havoc at the southern end of what was then its southern gulf. Things were already lively down there, as increased tectonic and volcanic activity had been going on from 11 to 9 million years ago in the Red Sea and Afar triangle, all the way down the East African rift (this is about when we last shared a common ancestor with the gorilla).

While the sea-level fluctuations were still going on about 7 million years ago, the African plate moved away from the Arabian plate and the Danakil Alps microplate was no longer squeezed between the giants. Like the crustal blocks in Nevada that one can see driving north from Las Vegas in the Basin and Range country, where spreading is also occurring, the Danakil Alps have tilted vertiginously so that their sediment layers are now at a dramatic angle; they also swiveled counterclockwise into their present position. Just one of nature's little rearrangements of things that pointedly reminds you that blocks of earth can bob around like icebergs before getting frozen into place again.

When the Danakil microplate finally detached from both the African and Arabian plates, the sea flowed in and that was the end of the great Miocene land bridge between Africa and Eurasia. Not only did the Red Sea come down into the northern part of the Afar triangle about 6.7 million years ago, but the Gulf of Aden came up from the south and joined it, opening up the Red Sea (which had now lost its connection to the Med as the Isthmus of Suez arose). The Red Sea opened into the Indian Ocean via both the present Strait of Bab al Mandab and the "Danakil Straits" to the west. The Danakil Alps became an island.

DANAKIL WAS A LARGE ISLAND, potentially twice the size of such familiar islands as Sardinia, Corsica, Jamaica, and Puerto Rico. It perhaps became a series of islands as volcanos popped up here and there, as coral reefs formed, as tilting land subsided to near sea level; if so, they covered an area like that of the major part of the Hawaiian island chain. The Hawaiian islands are also a good comparison because they are tropical -- and they have volcanos that push their way up to altitudes that catch rain clouds, and so provide streams of fresh water for drinking.

The apes trapped on the islands would have had problems, and not just from all of the exciting volcanos and earthquakes. The late Miocene was a worldwide time of drying up, when the forests changed to grassy plains, even desert. While there was likely a savannah period on Danakil, the major food resources might not have been in the center of the islands but along their shores. For those who have not stuck a face-mask underwater in the Red Sea, it may be hard to appreciate just how luxurious sea life can become. While there are nice examples of coral-reef life to be seen in Hawaii and the Caribbean, the protected Red Sea is an order of magnitude more dense in its underwater life, comparable only to Australia's Great Barrier Reef. And one doesn't have to take a boat ride to an offshore reef to see Red Sea coral reef life -- it is everywhere.

Just wading in the shallows of the Red Sea can be like walking through a supermarket for fish and shellfish. There is seemingly limitless food for the taking. It's not just clams and scallops and mussels and oysters, with the sorts of hard shells that might accumulate for the archaeologists to find as middens (but, unless carried back to a central site before consumption, were more likely to be thrown back into the water, and swept away by the tides). Apes there might also have dined royally on fresh lobsters and crabs, could cooperatively have herded whole schools of reef fish into the shallows where they could be grabbed. Some fish, such as the grouper, would have been particularly favored, for both their taste and their large size. True, by wading the apes wouldn't encounter too many of the big fish, but surface diving would allow them to spear some inside the reef caves. Just as chimpanzees fish today for termites with a stick, so Danakil apes might have learned to probe for fish with selected spearlike sticks.

And one must not forget the tides. Near the mouth of the Red Sea, the tides might have been large, just as they are near the mouth of Puget Sound. Every day up around Seattle and Vancouver, the beaches are uncovered to a depth of one story. With tides like these, many stranded animals are exposed to even the most hydrophobic land-dweller -- which might be how the apes got started on a seafood career. While the tidal range tends to diminish with distance from the outlet to the sea (tides are minor up at Suez and Eilat), Danakil was in an optimal place for the exposed intertidal beaches to serve as an inducement to apes. Just as the little shrimp-like amphipods of the Colorado attract the whiptail lizards at low tide.

This is, of course, a description of what Danakil might have been like in the good times. All of the geological rearrangements of the Miocene-Pliocene boundary probably produced disruptions; furthermore, shellfish populations seem to be periodically decimated by diseases. Life on Danakil might have gotten harsh, periodically selecting for apes able to swim offshore, and dive deeper and deeper to find increasingly scarce food.

About 5.4 million years ago, lava flows along the southwest coast probably closed the Danakil Strait and reconnected Danakil Island to the African mainland. The extensive basalts would have made this base of the Danakil peninsula a biological desert for some time, still providing something of a barrier to the migration of land animals who had to eat their way along the surface. But, of course, the aquatic apes could have eaten their way along the shoreline -- provided there was drinking water in creeks.

So from 6.7 to 5.4 million years ago, the Danakil region would have been particularly isolated. Did some ape evolution occur there, which split the hominid line off from the apes? The chimps' DNA differences from humans suggest that the split occurred 7.7 to 6.3 million years ago, nicely overlapping the Danakil isolation period.

ONE EARLY HOMINID SCENARIO thus looks remarkably like the Hardy hypothesis, if Danakil is accepted as an ideal spot for ape evolution to take place. On the grounds of evolutionary biology, it is ideal for a number of reasons. The Danakil apes would have been isolated from the African ape gene pool, allowing natural selection to quickly bias the genome in the direction of the traits under selection. The population would have been small enough for speciation to occur; a series of islands might even allow for multiple species of hominids to form, with subsequent mixing as in the Galapagos birds and Hawaiian flies, with occasional replacement of the less "fit" species. There too, waves of selection might have taken place if the Red Sea dried up with the Med, then refilled, as the Danakil Strait opened and then closed periodically as lava flows crossed Danakil's southwestern coast. The drying up and the volcanos and changing tidal patterns would have made the plentiful sea life occasionally scarce, reducing the Danakil ape population to only the most fit. Evolution could have operated rapidly there, much more so than in the savannah of East Africa itself.

And what would have been the traits enhanced by natural selection? Wading ability, certainly, but eventually swimming and diving skills, an ability to remain in the water for a long time, perhaps even to babysit infants there. Angular hairy apes would not have fared as well as naked, curvaceous apes insulated with subcutaneous fat. Those with a pelvis that allowed their legs to be operated parallel to the spine would have been better waders and swimmers than the typical apes, and thus better providers for their offspring. Those with an improved sense of balance would have been better at exploring the underwater environment with its subtle gravity. And those able to control their breathing would have eventually been able to dive; a diving reflex would have let them stay down even longer. Hard times could have selected for such abilities. Toolmaking doesn't really appear in this scenario, as the chimp's hammering abilities with nuts would seem adequate for pounding shells open, just as the chimp's probing of termite nests with a stick serves as a model for spearfishing in reef caves (even birds poke sticks into holes, as Dan Hartline mentioned on the first day of our trip). These kinds of tool use really don't demand much toolmaking, though of course it might have incidentally occurred, as when the chimp flakes a rock that it was using to hammer open a particularly hard nut.

Nor do the needed adaptations particularly demand bigger brains -- though it has been noted that mammals that became aquatic often wound up with bigger brains in the bargain, as if the acquisition of an entirely new locomotor repertoire were facilitated by some extra brain in which to house the new neural-command machinery. The river-swimming monkey of the Gabon, the talapoin, has a significantly larger brain than an average Old World monkey of the same body size. With few fossil ape braincases from the period of 4 to 16 million years ago, we have no idea of when the hominid brain size started increasing, whether the 500 cubic centimeter ballpark was attained early, or whether it occurred shortly before 4 million years ago. But some brain growth is consistent with the aquatic ape hypothesis.

So the Danakil version of the aquatic hypothesis suggests that natural selection acted on a number of ape features independently in a mosaic fashion, but particularly on hair and fat, locomotion abilities, and diving physiology. It suggests that quite a number of rounds of speciation and selection could have taken place within several million years, thanks to the island setting, its unsettled geology, the end of the Miocene climate, and the poor Med's periodic problems with the erratic Straits of Gibraltar. We need only look at how fast artificial selection can reshape domestic animals to realize that a million years was probably enough time in which to make all those changes, given the opportunities for repeated selection and speciation. Even if rapid natural selection is a thousand times slower than artificial selection, there's still time.

The result would have been an ape-hominid with a number of omnivorous adaptations; we need not talk of intelligence to recognize that this might have been a cleverer animal, retaining the earlier ape fruit- and plant-eating versatility but with an overlay of new skills related to living along waterways and regularly eating the flesh of a number of species, acquired in a number of different ways. It would have been an animal capable of filling various African niches, more capable of improvising in hard times.

If they were going to venture forth from Danakil, these aquatic apes might well have brought along some disadvantages from their aquatic interlude, such as the naked skin and the salt- and water-wasting sweat glands, such as the need to keep an arm occupied by holding an infant who could no longer hang on, such as an inability to run as fast as its quadrupedal ancestors. The logical emigration routes would have been along the Red Sea shoreline. But, particularly if it were a bad year for shellfish, the apes could also have gone inland, up the Afar triangle following the Awash River valley upstream past such places as Lucy's home of Hadar. Then perhaps south down the Omo valley to Lake Turkana, further along the rift to Olduvai and Laetolil, even all the way down the Great Rift Valley to South Africa and the Transvaal caves. Actually, one cannot conclude anything about the rift being a favored path of migration for hominids, as the rest of Africa is largely unexplored and negative evidence from it means nothing. The rift is the favorite site in which to dig because it is pulling apart, tilting strata in the earth's crust, and exposing the 1-4 million year old sediments so that you need not dig down twenty stories to find them. So one has to take the Great Rift Valley as something of a special case -- but maybe the case, where it all happened.

The salt of those ancient seas is in our blood, its lime is in our bones. Every time we walk along a beach some ancient urge disturbs us so that we find ourselves shedding shoes and garments, or scavenging among seaweed and whitened timbers like the homesick refugees of a long war.
...... LOREN EISELEY, The Unexpected Universe, 1969.

BACK 34 MILLION YEARS AGO, apes evolved from the Old World monkeys, losing their tails, gaining a shoulder joint of increased flexibility. But there is more to the monkey-to-ape transition than just cherry-picking and some increase in brain size. More impressive to behavioral scientists is the doubling of the length of childhood. Monkeys may reach sexual maturity in 3 to 4 years, chimps need 7 to 8.

Now if one wants to teach by example, to pass on memes as well as genes, that's very important. Not only do more things happen in twice as many years of childhood, but there is also the fact that juveniles are primed to play, to mimic. The Japanese macaques --the same ones that washed the potatoes and sifted the sand out of the wheat -- demonstrate that the young are more likely to experiment with a new technique, eat a new food. The older animals then copy them, except for the old males who seem particularly inflexible.

Playing around is not universally a good thing -- one often has to take action without thinking, instinctively do the right thing on the basis of inborn or acquired propensities. When one is old enough to have offspring, one had best be able to forage efficiently rather than fiddling around half the time. Because the young are protected by more serious-minded adults, they can afford to play around. And twice as long a play period, before becoming a more reliable adult, was great as long as the species could afford it.

Ah, but that's the rub, it seems. Barbara pointed out that the remaining apes have seemingly overdone the extended childhood. A chimp female may have to wait six years before bearing another offspring because ovulation is suppressed by suckling -- which is a good thing, since she simply can't look after more than one at a time. Because of the infant and juvenile mortality, a mother may have trouble getting two offspring to reproductive age before she passes from the scene herself. Given that the mother chimp has to do all the work of child-rearing, it would be hard for chimps to ever expand their population, even in good years. Even without the situation created by the expanding human populations near their tropical habitats, the apes are marginal. They are excellent candidates for extinction, given some bad years. That's not only a serious matter for them but for us as well; because behavior does not fossilize, the apes are our best clues to what we once were, to what we could alternatively have become. We need to see how they cope in the wild as part of their native ecosystems, not just in the artificial setting of the zoo or circus.

Humans have gone even further than apes and doubled childhood again. However, child spacing has been reduced to every four years in primitive hunter-gatherer tribes, with further reductions possible in agricultural societies.

"But we've doubled the length of childhood, compared to the apes," Rosalie said. "How did we do that without having 10 or 12 years between babies?"

"That's right," added Abby. "Even in primitive hunter-gatherer tribes, the birth spacing is about four years. So it isn't agriculture that did it, though that may be why the birth spacing can drop down to two years in modern times."

"In a word," Barbara said with a big smile, "Lovejoy. That's the reason."

"Is that a person or a process?", asked Ben, suspiciously.

"Both," Barbara chuckled. "It's C. Owen Lovejoy, who's a physical anthropologist. But it's also a key feature of his -- and some other peoples' -- theory that accounts for how we've overcome the bind that the apes got themselves into." We all listened more carefully, I thought, wanting to know what either love or joy had to do with population ecology.

"Back to the birds," Barbara began. "As you all know, one of the traditional strategies for promoting one's genes is to spread them around as widely as possible, even indiscriminately. But there is also another strategy, to care for those genes after the birth of one's offspring and help assure their survival. Females often practice it. Males sometimes do, typically in situations where they can be sure the young are carrying their genes and not some other male's."

"I've seen male frogs that brood tadpoles in a special throat sac," added Ben. "And male birds may sit on nests, too. The males may bring home food to the young, sometimes to a stay-at-home mother too."

"Aha, but that's birds for you. Monogamy -- because the male is investing in babies which indeed carry his own genes -- is one way of making it worth the male's while to babysit and provide. Something like 92 percent of bird species are monogamous, while a mere 5 percent of mammals are. One ape is monogamous, the gibbon, but we parted company with gibbons about 22 million years ago, and none of our more immediate ancestors seem to believe in monogamy."

Our closest relatives, the African apes, do not excel in one-on-one relationships; male gorillas have contests for temporary possession of a harem, leading to sexual selection for big males. They are now twice as large as the females, when adult. The chimps have their multimale mating system in which the sperm instead compete in a lottery outside the ovum. Only the pygmy chimps are reported to have longer-term male-female relationships.

Even without monogamy, ape males are somewhat useful in caring for their young. In particular, they protect the troop. But a male may not have a way of promoting his particular genes: he most likely does not know which young he fathered, unless he is the longtime proprietor of a harem. And he seldom helps out with the food -- a chimp or gorilla mother finds her own food and that for the infants and juveniles. So his postconception efforts do not promote the survival of his particular gene combinations over those of the other males in the troop. A mother's efforts, on the other hand, go preferentially to infants carrying her genes; her pre- and post-conception success promotes her gene combinations. His pre-conception efforts promote his genes, but he needs to stick alongside those genes as the mother does if his post-conception success is to help them along up to reproductive age. The birds seem to have discovered this principle in a big way.

"What got monogamy started, given that's it's so useful?", asked Abby. "I can see why it has advantages, such as supporting the longer childhood, or the offspring of a particularly fit male surviving better through his postconception efforts. But what converted hominids to monogamy?"

"Well, you can see a minor form of one-on-one in the chimps, which might have developed into real monogamy in other extinct apes," answered Barbara. "When a female chimpanzee is in estrus she is often followed around for days by one or two males. Occasionally a pair will even disappear into the bushes for a few days. That's called a 'consort relationship.' If the female climbs a nut tree, the consorting male will likely find something important to do up the same tree. While the female doesn't spurn the advances of other males, the consorting male probably gets quite a few more sperm into the lottery, besides being more likely to be there at ovulation time."

"Now suppose," she continued, "that a female happened not to advertise her time of ovulation -- human females don't, which is a big puzzle, since it is unusual among the primates. Ovulation occurs halfway between menstruations...."

"Is that the same as estrus?", Abby asked.

"Yes, the behaviors you see at about ovulation time are simply called estrus," Barbara replied. "Instead, the prehuman female seems to have become sexually receptive all the time, with the time of ovulation neither marked for all to see by sexual swellings on her rump -- which is what most monkeys and apes do -- nor advertised by changes in her behavior. No more estrus."

"Now what would have been the consequence of such a genetic variant?", Barbara asked her attentive audience. "The male most likely to impregnate her would be the one who followed her around and tried regularly. The concealed ovulation -- that's what this lack of estrus at ovulation time gets called -- in females would then select for a certain variant type of male, one who consorted and tried regularly."

"Hah! So that's where 'lovejoy' comes in!", exclaimed Ben, laughing.

"That's the idea. Presumably the sex drive became strong enough to sustain all this time-consuming, out-of-season mating activity," Barbara said, smiling. "After all, the oviducts are empty, conception can't occur. Few other species waste a lot of time and energy mating when it serves no purpose."

"It sure would select for males that stuck close to a favorite female," Rosalie said, "because they'd be more likely to impregnate the female with concealed ovulation. We seem to have lost salt hunger, but we have certainly enhanced sex hunger."

If we could interview a chimpanzee about the behavioural differences separating us, [food sharing] might well be the item it found most impressive -- "These humans get food and instead of eating it promptly like any sensible ape, they haul it off and share it with others.
.......the archaeologist GLYNN LLYWELYN ISAAC (1937-1985)
SURELY THE KEY ASPECT of concealed ovulation exposed to natural selection -- as Richard Alexander and Katherine Noonan noted in 1979 -- would be the provisioning and infant care into which it led the male. For monogamy to evolve in the hominids, consorting would have to have become a real habit, a substantial one-on-one attachment, something like mothers develop for their infants, that would bond a prospective father to the mother gestating his genes in the manner of bird monogamy. Did the females set this up by rewarding food gifts with sexual receptivity, much as the mating rituals of many birds involve displays of masculine skill at nest-building, with sexual receptivity the reward for satisfactory building skills?

The ape females whose genes led them to reward food gifts and companionship would certainly have been more likely to have a well-fed infant if the consort relationship continued. Nor need this have been the direct type of short-term deal suggested by modern prostitution; the usefulness of a consort relationship would instead only seem to require a correlation, such as the female being more likely to consort with a male who had meat to share than one who didn't. Just being around her more, he'd get more tickets to the pregnancy lottery.

One must focus on plausible lines of evolution, the things that lead to explaining some of the major differences between us and the African apes. Those differences include concealed ovulation, virtually nonstop sexual receptivity, pair-bonding, and male provisioning. Somehow those developments occurred by the usual genetic mutations and permutations. Somehow they became more prevalent via the usual natural or sexual selection processes. And they were probably conserved now and then by speciation.

But when did they occur? Early, middle, or late in hominid evolution? Before the chimp split, with the chimp perversely retrogressing later? During a Danakil-like pre-Australopithecine interlude? After Australopithecus afarensis went walking upright back to the savannah, but before the brain started to enlarge? Or during the spectacular period of brain enlargement of the last 2 million years? The fossil evidence is thin but not entirely silent: rather like gorillas, A. afarensis had a much greater degree of sexual dimorphism than modern humans (some experts say; others interpret the size range as not male-female but two different species). If A. afarensis did have sexual dimorphism of a considerable extent, that would suggest an earlier period of harem-type mating systems, not a prolonged period in which monogamy had stopped sexual selection for overblown males.

An argument can be made that our tendencies toward monogamy developed initially in the period between 5 and 3 million years ago, during the aquatic ape's readaptation to the highlands and river valleys of East Africa proper. The Tierra del Fuego practices suggest that floating childcare is not incompatible with the mother gathering food by wading and diving, so the Danakil ape females might well have managed to provide for themselves and their offspring in the usual ape manner, without a home base or male provisioning or delayed consumption. But in subsequently coping with the savannah, an arm (and an upright posture) would often be continuously required to carry an infant that couldn't cling to the now-missing maternal fur. It would be harder to park the infant while gathering, what with the carnivorous predators of the savannah. The mother could, as some human mothers still do, take the children out gathering with her, but they would wind up with a meat-poor diet -- just those small animals and birds that she could grab in the underbrush in the manner used by baboons (when the infant didn't cry at the wrong time). The ape's taste buds might have been attuned to the regular taste of calorie-rich flesh by then. The males, able to range more widely and engage in longer chases because they lacked immediate responsibility for the children, would be more likely to possess meat in the chimpanzee manner.

Consort relationships might very well hinge on who happened to have tasty meat, an extension of the chimpanzee's tolerated scrounging for meat; the female and juvenile have-nots beg the typically male possessors for a handout; it's the most prominent food-sharing seen in apes outside of mothers and their infants. Add concealed ovulation to this food-sharing ape, and one has a scenario for the development of male provisioning of the mother and her offspring. And thus for developing the full benefits of two-parent investment: the offspring survival based on the father's (as well as the mother's) postconception performance a la birds but also the doubling of childhood.

THAT'S MY PRE-ENCEPHALIZATION HOMINID SCENARIO, borrowing heavily from Alexander and Noonan, Lovejoy and other biologists and anthropologists who have thought about the matter. No doubt others can fit the pieces together in other ways, perhaps for the other possible time frames just as well. You'll note that I've divided up the post-common-ancestor period into an early (aquatic, upright?) phase and a middle (savannah, monogamy?) phase; there is also a late bigger-brain phase (temperate zones, hunting?). Each phase was about 2 million years long, underway by perhaps 6.5, 4.5, and 2.5 million years ago, respectively.

We decided that one important feature would make a good slogan for our T-shirt philosophy sweepstakes: CONCEALED OVULATION WAS RESPONSIBLE. Though people would probably misinterpret it too, thinking it merely appropriate for wearing by an expectant mother who had been using the rhythm method of contraception.

All this pervasive sexual activity is, of course, what humans usually think that sex is all about. But this is largely nonreproductive sexual activity, when the oviducts are empty, the female unable to conceive on more than 80 percent of such occasions. It really has to do with pair-bonding for raising children and lengthening childhood, not with making another baby. And it's ironic: in such elaborations of the concealed ovulation hypothesis, the nonreproductive aspects of sexual activity emerge as the distinctly non-ape human feature that made two-parent families possible. But biology having been only partially understood by some religious groups, they insist that sexual activity be firmly linked to reproduction -- as in the barnyard. One would think that if they wanted to promote family life rather than just more babies, they'd be in favor of nature's own nonreproductive sexual activity, in favor of birth-control devices that would let pair-bonding continue when reproduction had run its desired course but there were not-yet-grown children to rear. To say that nonreproductive sex is unnatural is to misunderstand one of the things that made us human -- indeed, an aspect that the church most cherishes, family life.

SURPRISE VALLEY was as far as Alan and his companions went, they report upon returning. They ran into the hikers making the loop up in the bowl-shaped valley who had spent some time exploring the Anasazi ruins. And playing around Thunder Spring.

In the boat during the half mile from Deer Creek down to camp, we ran wild making up more T-shirt slogans after explaining CONCEALED OVULATION WAS RESPONSIBLE to the hikers. DIG AT DANAKIL! was what got us started. USE YOUR COLORADO MATTER to promote the gray matter's new name? Here we go again. I can just imagine what they'll think at the T-shirt store when we get back to Flag. THINK STOCHASTIC! Silliness has struck again.

Everything that happens now in churches, schools, town halls, and theaters happened concentrated and intense and all at once in the caves. It was the only way in those days to create a human unity, a body of conforming and obeying people. People who were individuals in the modern sense could never have survived.
...... JOHN E. PFEIFFER, The Creative Explosion, 1982.

Mile 137
Overhang Camp
Ninth Campsite

ROSALIE CAST A CRITIC'S EYE on the sandy beach, which was shadowed from the afternoon sun by a great overhanging slab of rock where the river had undercut the cliff. It formed a giant cave, with space enough for everyone to spread their sleeping bags, even for the kitchen as well. No tent to pitch tonight. It seemed unlikely that river-runners were its first inhabitants, nor the first to name it Overhang Camp.

"I don't know about those Anasazi," Rosalie said, hand on hip, looking up at the overhang. "First, little caves in steep cliff faces, only forty stories down to the water. Straight down. Now this -- lots of room for all the relatives, but with the river so close that it probably cleaned house for them every spring. Thus depriving archaeologists of their due, the trash pile." She turned away and looked back at us as we leaned against the boats, laughing and sipping refreshments. "I'm afraid that Anasazi dwellings remind me of that classic architectural description in the New Yorker that called somebody's homely masterpiece -- let's see if I can remember the quote -- 'an anomalous piece of domestic architecture, combining the small, familiar pleasures of the hearth with the headier excitements of Doomsday'."

After the laughter had died down, J.B. tossed her a cold beer from the bilges of his boat. "Actually," he said, "Overhang Camp has a reputation to maintain. We don't call it Hangover Camp the next day for nothing."

"Ah," Ben exclaimed, "now we see the true origins of the word Hangover. A twisted tongue, contorted by the evil brew. Did the Indians brew beer?"

"They probably discovered it by accident, storing grain in jars that somehow got filled up with rainwater and fermented away," Cam ventured.

"Maybe they got their antibiotics by accident that way too," Rosalie smiled. "Grain storage bins like those Nankoweap granaries are great places for mold-like bacteria such as Streptomycetes to grow. They're present in soil and they like a very dry, warm, alkaline environment. And they produce tetracycline to use in their war for survival competing with other bacteria. Fouls up water regulation in other bacterial cells, so they swell up and go pop. If you use grain from such contaminated granaries, you can get an incidental dose of antibiotic with your beer and your bread. Every day. Makes your resident bacteria go pop too."

But did the Indians really get antibiotics that way, we asked?

"Well, the Nubians of the Sudan apparently did about 1,600 years ago. One of the peculiarities of tetracycline is that it likes bone, binding to the calcium and forming compounds which, it just happens, fluoresce. And bones from an old cemetery near the Nile River show the characteristic tetracycline fluorescence. Debra Martin discovered that quite by accident when she went to look at some thin slices of bone to make a routine measurement of wall thickness. Now normally you wouldn't use a fluorescence microscope for a routine job like that because their light bulbs are so expensive and burn out so fast. But the only microscope that wasn't busy was a fluorescence microscope, so she used it. And when she turned on the microscope's ultraviolet light source, the bone lit up like a fluorescent Christmas tree, just like it would from bone biopsies in patients treated with modern tetracycline."

"Were these mummies?"

"They were naturally mummified by the dry desert air, but there was none of the fancy Egyptian embalming. No, contamination isn't likely the cause. And it wasn't just a few of the bones that showed the fluorescence, as would happen if you studied a modern autopsy series -- so far, all the bones from that cemetery have the tetracycline. Suggesting that they all got it as food contamination or as some other sort of environmental pollution."

"I always said," volunteered J.B., "that beer was good for you. Sounds like old-fashioned beer was even better."

"So did the Nubians grow bigger faster, just like the cattle and pigs that farmers now dose routinely with tetracycline?" Sue Gilmore interjected. "You know, half of the antibiotics produced these days go to fattening up healthy animals for market. It probably works because it suppresses the subclinical infections that otherwise slow down growth."

"Well, ancient cemeteries have been studied pretty extensively by the anthropologists who are interested in ancient disease patterns. And they say that the Nubians had extremely low rates of infectious disease," Rosalie replied. "Of course, they might have suffered from some of the typical side effects of tetracycline too -- such as when your intestinal bacteria get killed off and you think you have dysentery. Tetracycline also slows down sperm, and extended exposure reduces the number of sperm produced. Bone growth in infants can be slowed. Vitamin B can be depleted. You don't want to take it unless you have to."

"Yet the widespread use of antibiotics nowadays -- both from adding it to the feed of healthy farm animals and from the underdeveloped countries selling it over-the-counter, so that it gets taken routinely as a cure-all -- is causing a really serious problem," Rosalie continued. "It results, because of good old Darwinian natural selection, in bacteria that no longer burst open and die when the antibiotic gets to them. These resistant strains of bacteria aren't created by our antibiotics. But the antibiotics kill off the competition, so that the otherwise-rare resistant ones prosper. The indiscriminate use of antibiotics is capable of putting us right back where we were before such wonder drugs were developed. And that affects you, not just the people who abuse the antibiotics -- you won't be cured by the antibiotics anymore either. So you've got an interest in what the users do with them -- you can't take the live-and-let-live attitude you might otherwise adopt toward drug users".

Rosalie sipped her can of beer. "Now when this problem started popping up, such as in that cholera epidemic in Mexico where they were frantic because a lot of patients didn't respond to the usual drugs, people thought that resistance was new, dating from the widespread use of antibiotics after World War II. But then they found that 'virgin' populations, supposedly never before exposed to antibiotics, also had some resistance factors in the cytoplasm of their cells. So maybe indiscriminate use of antibiotics has been around for a long time, at least in desert peoples who irrigated fields to raise grain and then stored it for long periods in hot, dry, dirty storage bins."

"Did the Anasazi get dosed with tetracycline too?", asked Marsha.

"So far as I know, no one has checked Anasazi bones yet -- maybe you should investigate that yourself. This is a perfect setup for it," Rosalie gestured at the surrounding canyon, "with the same desert climate that should make Streptomycetes commonplace, with the Anasazi irrigating the fields much like the Nubians, using mud-lined granaries and such. Maybe. It's a real possibility."

"Can you just eat Sudanese desert dirt and get a good dose of tetracycline?" Sue ventured. "They probably didn't always wash off their food, so they might have gotten a dose that way too."

"Well, if you place a bit of the soil in a culture dish, it sometimes shows obvious antibiotic activity, inhibiting the growth of bacteria in a zone around it. I don't know how much soil you'd have to eat to get a decent dose, or what the side effects of eating that much dirt might be," she laughed. "The advantage of a storage bin full of grain is probably that it provides excellent culture conditions, a protected place with lots of nutrients. See, Marsha, there are all sorts of things left for you to discover."

He prayeth best who loveth best
All creatures great and small.
The Streptococcus is the test
I love him least of all.

LIVING IN CAVES has probably been around as long as there have been both caves and humans. Cats and bears, sloths and birds -- everyone likes a good cave. And from the standpoint of humans, a cave sometimes came with an additional advantage: a floor that helped keep the campfire burning. Bird and bat guano accumulates on cave floors, which are sometimes mined for making gunpowder. The problem could have been in keeping the fire under control. The New Yorker's critic would have had a field day: the caveman's humble abode with its homely hearth might indeed have produced the headier excitements of Doomsday. Booms-day?

So the earliest cavemen might have been Australopithecus afarensis, if they could have found a cave. Certainly Neanderthals liked caves. And we're the latest cavemen, spread out here under Hangover. I mean Overhang. Oops.

Not too much happened for several million years or so after upright posture developed -- so far as we know, that is. Hominids were upright by 4 million years ago, maybe even earlier. But the next bit of hard evidence of progression isn't until about 2 million years ago. And that, to our eyes, is impressive -- tools and brains blossom.

Starting about then, stone tools became plentiful, the kinds of flakes and remaining half-stone fragments that Barbara made back at Monument Creek after that eventful day. They haven't been found earlier, though the hominids might well have been using tools without making them in Barbara's manner, which results in lots of leftovers for archaeologists to find. They probably enjoyed nuts, and worked to crack them with the same techniques employed by the chimpanzees today, using a handy stick or stone as a hammer. But a hammerstone, unless the same one is employed regularly, doesn't acquire the pockmarkings that would label it as an artifact; indeed, were such a stone found in a 4-million-year-old context, one would have to consider whether a chimpanzee might have used it rather than a hominid.

Besides this stone-flake evidence of hominid toolmaking at 2 million years, the size of the brain is also seen to undergo some enlargement. Nothing dramatic, mind you. Indeed, it is only in retrospect that one would affix a date for the enlargement as having started between 2 and 3 million years ago. If you plot brain size from 2 million years ago to the present, you can fit a straight line that suggests a regular increase in brain size from 500 cubic centimeters (473 cc is a truly pint-sized brain) up through the recent 1500 cc of the Neanderthals. Extrapolate the curve backwards in time, and it will suggest that 4 million years ago, we had no brains at all.

But brain size stays at 500 cc from 4- to about 2.4-million years ago, then curves upwards and meets the straight line fitted through the points from later hominids. As it happens, 300 to 500 cc is also the adult brain size of the modern chimps and gorillas, so it is often said that hominids had ape-sized brains until then. One wonders what was selecting for bigger brains back around 2.4- to 2.0-million years ago.

Tools? That's the other thing we know was happening then. And the sea-floor oxygen samples suggest that the mini-ice-ages were getting started back then, as early as 3 million years ago. But we must not let the hard evidence bias our view too much. Just think of all the things that don't fossilize, the artifacts that reliably crumble into dust. There were probably wooden spears long before rock spear tips appear in the archaeological record. And hunters were probably throwing handy stones, knocking down rabbits and birds, long before they accurately threw specially shaped rocks or spears.

Gathering was probably once even more important than hunting, but split-cobble-sharpened digging sticks aren't preserved either. Waterbags from animal bladders aren't preserved. One of the key inventions, the anthropologist Richard Lee notes, may have been the carrying bag. If you've got to carry food back to a home base to feed your family, you can only carry so many separate items in your hands and arms. A sack or a basket is very handy, once you pick up more than four items at the grocery store. And the carrying bag is handy for hunting too -- it allows the hunter to carry along a supply of familiar, favorite throwing rocks. Without it, a hunter would only get several tries before having to resort to whatever rocks were lying around nearby. But carrying bags aren't preserved for very long. We can go look at the deteriorating, thousand-year-old Anasazi carrying bags at the local museums, but not those of the African hominids. Did the post-aquatic women invent them for baby slings, then adapt them for shopping bags? It seems likely, but we'll never know for sure.

Now the big thing that happens after this blossoming of brains and toolmaking in Australopithecines is the first multi-track hominid experiment. Just as there are currently two ape species in East Africa (chimp and gorilla), there were once three quite different species of hominid living there at the same time, in about the same places. Starting at about 2.0 million years ago, there was Homo habilis who lasted until about 1.7 million years ago. Then there was Homo erectus, the even larger-brained successor to Homo habilis, seen as early as 1.75 million years ago. And continuing until 1.4 million years was a more robust form of the earlier Australopithecine, what Louis Leakey initially called Zinjanthropus.

In Zinj and his relatives, the molar teeth's grinding area was doubled rather than the brain size. Zinj was generally heavily built, as in the gorilla-like sagittal crest running along the top of his head, needed to anchor his massive jaw-closing muscles. The newspapers called Zinj "Nutcracker Man" because of that formidable chewing apparatus, though surely Zinj had better ways of cracking nuts than by trying to chew them whole. Big grinding surfaces like that suggest high-bulk, fibrous diets, such as those leafy plants that modern gorillas consume daily in large numbers (they must eat about 27 kilograms -- 60 pounds -- each day). Zinj and relatives died out by 1.4 million years ago, leaving Homo erectus with its 800 cubic centimeter brain as the only hominid on the scene. The triumph of brain over brawn? A change in climate wiping out Zinj's major plant food, with Zinj too inflexible to try other foods? Who knows? Also, no one knows where the new species came from; LaLumiere suggests that Homo habilis might have been the latest arrival from Danakil, if it was still in business producing new species from its lava-isolated section of Red Sea coastline.

One of the specific characteristics of the human evolutionary lineage has been the propensity to make tools -- and to discard them. This has created a trail of litter that can be traced back some 2 to 2.5 million years.
.......the archaeologist GLYNN LLYWELYN ISAAC (1937-1985)
INDIRECT TOOLMAKING, as opposed to our usual notions of careful craftsmanship, may have been the way rock toolmaking got started. Not only chimps but hominids might have pounded nuts open with rocks that fractured -- and might have found a use for the sharp edges of the fractured rock. Glynn Isaac's model of pounding two stones together for a while, then sorting through the fragments for particularly useful ones, would be a more advanced type of "stochastic toolmaking." The profusion of stone fragments seen starting about 2 million years ago may simply represent the advance from incidental to intentional fracturing.

The basic choppers, scrapers, and flakes seen at the earliest toolmaking sites, Olduvai Gorge and Lake Turkana, were augmented gradually over the next half-million years. Then, at 1.5 million years ago, an interesting development occurred at Olduvai: just as we have no problem distinguishing the different styles of kitchen knives and silverware manufactured today, so archaeologists can distinguish a new style of toolmaking, which they call Acheulean. And like modern silverware styles, the Developed Oldowan and the Acheulean stone tool styles began a long coexistence. Eventually, more than a million years later, the Acheulean took over the market. And then was itself replaced by 0.3 and 0.1 million years ago, when a new style of toolmaking developed that involved more than just touching up selected broken rock fragments.

A GIANT ARROWHEAD pretty well describes the shape of an "Acheulean hand ax," a teardrop-shaped rock artifact that goes back 1.5 million years to the days of Homo erectus in Africa. While named after the find at Saint Acheul, France, the Acheulean hand ax has been found from Europe to South Africa, from the Mediterranean east through the Indian subcontinent to southeast Asia. It was evidently a popular item of the times, and its times lasted for well over a million years.

I can spread my fingers just about enough to reach from one end to the other of an average hand ax; sideways, it fits in the palm of my hand. Unlike the arrowhead, hand axes have no handle or attachment area; the back end is rounded like a discus. They are flat stones to start with, shaped by chipping away their edges into a taper. And therein lies the problem in believing that it was really used as an ax: because the sharpened edge extends all around, hammering something with one seems as likely to damage the hand as the target, not quite as bad as hammering on a double-edged razor blade, but the same general problem. Whoever named this artifact the "hand axe" must not have tried using it as one.

It is much easier to convince yourself that they were used for throwing. This was first proposed over a hundred years ago, and H.G. Wells even popularized the idea in his 1899 book, Tales of Time and Space. Flat stones have some nice aerodynamic properties, seen in the frisbee and the discus: because spin can stabilize such a projectile into an edge-on attitude to cut through the air, it can often be thrown farther than a round or irregular stone of the same weight, which will encounter more air resistance.

Small "hand axes" can be thrown overhand in a vertical orientation, and are said to be appropriate for hunting birds. A small hand ax is set spinning by holding it near its pointed end between the thumb and bent forefinger, and then flicking the wrist while uncocking the elbow. It may have been this method of setting the spin that required the teardrop shape. The largest hand axes are too awkward to throw overhand, but a discus thrower can do quite well with them. For her undergraduate honors thesis, the anthropologist Eileen O'Brien tried some experiments with a fiberglass replica of a 30 centimeter (1 foot) hand ax from East Africa, enlisting the aid of several varsity athletes. The typical distances achieved were more than 30 meters (about half a dozen parallel-parking spaces). Though starting off in a horizontal spin, the large hand ax would shift to vertical as it descended (what often happens when I throw a frisbee). And on nearly every throw, the hand ax would land on edge, sticking into the ground -- often, point first.

This tendency for the thrown replicas to land vertically may explain some puzzling aspects of the archaeology of hand axes: they are often found standing on edge. The most common place to find them is in what was once shallow water; yet the surrounding countryside may be barren of them. This would make sense if they were used to ambush game animals as they came to the water to drink. While one would expect a hunter to retrieve a favorite throwing stone, the ones that landed in the lake might not be found, accumulating there in the mud like so many lost golf balls (Indian arrowheads in North America similarly accumulated in shallow water). Only if they were projectiles would one expect such a shallow water distribution; if used as axes, there is no reason to expect to find them preferentially in the water. Especially standing on edge.

So I wonder if they weren't a stage in our development of throwing. I doubt that they were the earliest stage; perhaps they were an improvement on throwing peach-sized rocks. At East African sites dated to 2 million years ago, Mary Leakey finds groups of rocks that she calls manuports -- hand-carried -- that are suitable for throwing; they are not indigenous to the local geology, as if carried in from some distance. The primary advantage of a hand ax over a round rock is its narrow edge, important for aerodynamics. It is also true that such a shape would be the best way to get a heavy rock to travel any distance (a large hand ax may weigh 2 kilograms); though speed is theoretically a better way to achieve great stopping power than is weight -- because of the square-law relation of kinetic energy to velocity -- they might not have been able to achieve both speed and accuracy at an earlier stage in brain development.

It is unlikely that a large hand ax could be thrown sidearm with the same accuracy achieved using a dart-like overhand throw of a small round rock or small hand ax. Yet because of their weight, the large hand axes might have been efficient for knocking down a medium-sized game animal; striking anywhere on the body might delay the animal's escape long enough for the hunter to run up and grab it. A good aim might not initially be important if throwing into a whole herd of animals coming to drink at a waterhole; it wouldn't matter which one was hit. Clustering is one way that animals minimize their exposure to predators (only animals on the outside of the group are exposed, a small percentage of the total), but it would have worked against them, once throwing was invented and a hunter could lob a large stone onto their midst.

Modern humans are notoriously expert at killing from a distance. The hand ax may be proof that this behavioral strategy was refined long ago.... Is it possible that the ancient Greeks preserved as a sport [the discus throw] a tradition handed down from that distant yesterday?
......the anthropologist EILEEN M. O'BRIEN, 1984.

DESSERT AFTER DINNER featured a choice of cake and cookies. The cookies were the sandwich type known as Oreo. And so we toasted Oreopithecus with Oreo cookies, saluting all the sophisticated species that didn't make it.

Then Marsha suggested that perhaps Oreopithecus was the original cookie-monster.

HUNTER-GATHERERS OR GATHERER-HUNTERS? What was the major source of the hominid diet, meat or vegetables? The living apes are mainly gatherers; some are specialists in plant food, as are the gorilla and the orangutan, but chimpanzees are omnivores -- they'll eat much of what's seasonally available, except that wild chimps seem to pass up dead meat. Nice fresh meat is quite another matter -- chimps will skillfully stalk and kill antelope, small monkeys, and bush pigs, tear them apart and consume them with relish. But chimps too are primarily gatherers of seeds, leaves, blossoms, and fruit. Are chimps therefore gatherer-hunters (if we are to adopt the revisionist anthropological nomenclature which seeks to stress the vegetarian side of things over the carnivorous side)? Well no; gathering, to the anthropologists, suggests carrying the food back to share it with a family, and chimps forage and consume their food on the spot. To delay consumption is very unchimplike. Chimps carry unconsumed food, all right, but only to keep it away from other chimps, so they can eat it in peace while hiding back in the jungle.

One can eat meat without hunting -- it's called scavenging, and some anthropologists stress its probable role, since defleshing tool marks overlie carnivore tooth marks on some animal bones. It is clear, however, that some early peoples were primarily hunters -- perhaps not in Africa, where there are alternatives to hunting, but in colder climates where there just isn't any plant food available during some of the year, and the dead animals to available for scavenging wouldn't support very many people. Inuits were an extreme example of this hunting lifestyle around the Arctic Circle. Gathering is a problem up there -- even the berries are quite small. Only the grasses and shrubs grow well in such cold climates, but one cannot digest them without the enzymes and extra stomachs found in the digestive systems of grazing specialists. The easiest way to get those calories in grass is by eating the muscles they produce in a grazing animal. Or the muscles of a predator who got to the grazers beforehand.

There are presumably all the possible intermediate mixes of hunting and gathering; the question is which mix played the predominant role in hominid evolution? Which diet required advanced toolmaking and tool use, which diet demanded a bigger brain, a longer childhood, whatever?

And which diet is associated with the best opportunities to "make progress", to rapidly turn the ratchets of evolutionary change? Hominid brain enlargement, once it starts, progresses with extraordinary rapidity). Island seafood diets? Danakil provides one example, but there are other ways of getting the evolutionary advantages of islands as well.

A good case can be made for hunting as the most important hominid dietary source, simply because of the reliance in marginal climates upon meat. That's because margins are more important than population centers. Selection pressures are harsher in marginal climates, so change is more likely to be made by natural selection biasing the population towards those with important traits such as the ability to stalk and aim and throw. As the Inuit suggest, hunting skills may become terribly important in such climates, for keeping the family alive through the winter; they cannot fall back on gathering after missing the target, the way Africans could. And those essential-on-the-margins traits are also more likely to be made permanent by subsequent speciation, since they occur in isolated places where the gene pool isn't buffered by a large interbreeding population. On the margins, tribes are few and far between because the land won't support a higher population density.

While the gathering skills may be used more of the time in the tropics -- as many anthropologists are quick to point out whenever hunting is stressed -- the bias exerted there by natural selection is not likely to be as rapid or as harsh as in marginal regions . For one thing, there is no hunting-only winter once a year to nudge things along. Nor, when a bias towards more successful reproduction is finally achieved by natural selection in the tropics, is it likely to be made permanent, because speciation cannot readily occur with all the interbreeding opportunities, short of an island situation, such as in the Danakil aquatic ape hypothesis. The African savannah and forests, as well as other hominid sites such as in tropical Asia, will support higher population densities than the margins, preventing large deviations from the average that might make the genome idiosyncratic enough to speciate and preserve adaptations.

All this suggests looking for the real action in hominid evolution on the margins, places such as our Colorado Plateau -- say Unkar Delta -- where success was sporadic, life was chancy, where populations underwent boom and bust, where every bit of cleverness counted. Not that early hominids were ever around here (even their ancestors, the apes and the Old World monkeys, never made it across to the New World -- though some early primate teeth are to be found in Montana). But along with the lifestyle of the Inuits on the Ice Age frontiers, the lifestyle of the Anasazi on the mountainous desert frontiers serves better as a model for the cutting edge of hominid evolution than that of the tropical populations that have contributed most of the bones and stones to the anthropological record.

The hominids of equatorial Africa were probably the products of evolution that happened earlier on the African margins, beneficiaries of -- rather than participants in -- the important selection and speciation events. But because Africa doesn't extend very far south into the temperate latitudes (no further south than Mexico or Israel extends north), winters aren't very spectacular even in South Africa, making islands like Danakil especially important in African evolutionary considerations before the ice ages began. When ice ages altered climates world-wide, South Africa and some of the mountains around the Mediterranean Sea might have had more significant winters, nudging selection along each year in those subpopulations which couldn't retreat to the tropics.

It didn't always seem that way. Darwinian gradualism suggested that the center of the whole population was a representative place to look, as the low numbers on the margins meant that they didn't count very heavily in the average. But the progress in evolutionary theory over the last few decades has shown that Darwinian gradualism, while it may operate in small populations, does not realistically depict the detailed mechanism of the ratcheting up of a whole species, which involves a sequence in both space (the allopatric speciation of Mayr) and time (the punctuated equilibrium of Stanley, Eldredge, and Gould). That has implications for where to dig.

The people who dig in the tropical sun for years to find a few hominid bones will protest that this is unfair, that it asks them to instead dig where the population density was ten times lower and the geology or climate for preservation unfavorable, so that finds will be even rarer.

True, but it reminds one of the story about the person who was crawling around on the sidewalk under a streetlight, sorting through bits of broken glass while looking for a lost contact lens: That wasn't where he lost the contact lens, but the light was better there....

At the present stage of hominid investigations, the questions to answer about hominid origins are What and When -- and so it makes some sense to look where there's a chance of finding something, anything. But if we want to see hominid evolution in action -- to answer Where, Why, and How questions -- we'll eventually have to look in the right places. Even if the light is poor there.

Just as in contemporary industry, where the cutting edges of innovation (as well as high failure rates) often lie in small companies outside the big industrial cities, we may have to look where small groups struggle if we are to understand how lasting change comes about. The industrial centers may wind up doing the mass production which results in the most common artifacts which some future archaeologist of the computer age on Earth will dig up, but their antecedents will be hard to discern. IBM's best-selling computer, the PC, wasn't really designed or built by traditional IBM; it only stepped into a well-developed small computer field that was leaving it behind in the late 1970s, and packaged together a computer whose parts were designed and already being manufactured by small innovators. Hundreds of different small companies were taking those same disks, memories, displays, keyboards, and software, then integrating them into systems for small business use.

IBM did the same thing in 1981 but the familiarity of the IBM name captured the market in a classic bandwagon effect; only later did IBM begin manufacturing more of the parts themselves (many jokingly classified the IBM PC as an import, since many of its parts were made abroad -- but that's better than AT&T, which literally stuck their familiar name on a well-designed Italian computer). The buyers mostly thought that the computer was designed and built by those reliable, experienced engineers at IBM who made all those big computers. Actually, it was a small, temporary offshoot group that IBM set up in Florida which did the shopping and packaged the product (it wasn't even state-of-the-art for 1981). IBM cashed in on its name, not any special talent that the hundreds of smaller competitors lacked. That computer archaeologist will not, I hope, dig only near IBM headquarters in New York. As in hominid evolution, one has to distinguish between where the experiments and failures advance the technological evolution, and where the standardized mass production subsequently takes place.

THE BOATMEN ARE AT IT AGAIN. We are having a boat-jumping contest. The seven boats are, as usual, all pulled up, stern on the beach and bow in the water, parked side by side. One can, although barely, jump from the bow of one boat to the next bow. The target bow, of course, compresses into the water when you land -- and then stiffly rebounds. If you lose your balance, you fall into the shallow water, or perhaps the front compartment of the boat. Ordinary mortals wobble upon landing, and fall -- if they haven't already fallen while launching themselves.

Fueled by beer (presumably without tetracycline), the boatmen are getting a running start, hopping onto the first boat's left bow, then over to the right side, and then bouncing from one boat to the next, trying to get through all seven before crashing. To get an idea of the dimensions, imagine seven soft waterbeds strung out end-to-end, each with two standard-sized beer kegs on them to serve as the stepping stones. This is what the physicists call a gedanken ("thought") experiment; if someone, heaven forbid, should actually have seven waterbeds, fourteen beer kegs, and the space to string them out and get a running start, I disclaim all responsibility for the flood that will result.

Eventually all the boatmen try their luck, and a half-dozen passengers as well. Howie wears his white sheet as a cape. After a few practice runs, Alan and Jimmy get through all seven, to cheers. Everyone keeps trying, and eventually even the better-coordinated passengers like Dan Richard manage to get through seven bounces without falling.

Then Jimmy -- superbly coordinated Jimmy -- tries to do it on one foot. Well, he gets his running start with both feet, but then hops on his right foot from boat to boat, his leg pumping like a piston. On the third run, he makes it through all seven bouncy bows. What a finale. The Overhang cave resonates nicely to our shouts.

I wonder what the Anasazi improvised for athletic contests here? And when did such spontaneous contests begin in hominid evolution? One never sees apes performing in turn, cheering one another on, trying to better their performance on the next round. This is more than the usual monkey or ape playfulness. Maybe it happened during the hominid's redoubled childhood, during all that extra time to play.

A Tentative Timeline from Apes to Homo sapiens

7.0 Myr Chimp-Hominid Common Ancestor
Like chimp, perhaps already omnivorous and clever
Assume mother-infant family as African apes
Aquatic ape phase for hairlessness, upright posture?
Frequent selection cycles as volcanos, tides change and when shellfish supply ruined by pathogens
4.0 Myr Early savannah phase of Australopithecines
More helpless mothers due to carrying infants?
Concealed ovulation develops
Pair-bonding develops, male supports family too
Gathering, small game hunting as in chimps, baboons
Waterbag, carrying basket invented?
Throwing for threatening carnivores (defense, scavenging); minor selection for throwing accuracy
Selection cycles due to African drought, volcanic eruptions; every-winter cycle only in South Africa during some climatic periods or in "mountain islands" on slopes of high volcanos
2.4 to 2.0 Myr Brain size increase starts with Homo habilis
Hit-or-miss rock flaking for cutting tools
Major climate change every 0.1 Myr as ice ages come and go
1.5 Myr Discus-like "hand ax" throwing into herds at waterholes
Selection for length of throw, good aim not essential
Aimed throwing for hunting small, then larger animals
Continuing selection for accuracy, length of throw
Retouched toolmaking from broken stones; standard toolkit
Fire-starting from sparks during toolmaking?
Every-winter selection cycles for Homo erectus in temperate Europe, Asia; ice age oscillations continue
Continued selection for hunting abilities
Secondary uses of throwing and hammering neural machinery?
0.1 Myr Brain size increases ends with Homo sapiens
Shift from biological-plus-cultural evolution to cultural evolution alone.

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