The World Without Us - Alan Weisman (2007)

Part I

Chapter 6. The African Paradox

1. Sources

L

UCKILY FOR THE world after humans, not all the big mammals are gone. A continent-sized museum, Africa, still holds a striking collection. Would they spread across the planet after we’re gone? Could they replace what we finished off elsewhere, or even evolve to resemble those same lost creatures?

But first: If people come from Africa originally, why are elephants, giraffes, rhinos, and hippos even there at all? Why weren’t they killed off, like 94 percent of Australia’s large animal genera, most of them giant marsupials, or all the species that American paleontologists mourn?

Olorgesailie, site of the paleolithic tool factory discovered by Louis and Mary Leakey in 1944, is a dry yellow basin 45 miles southwest of Nairobi in the Eastern African Rift Valley. Much of it is dusted in white chalk from diatomaceous sediments, the stuff of swimming pool filters and kitty litter, composed of tiny fossilized exoskeletons of freshwater plankton.

The Leakeys saw that a lake had filled the Olorgesailie depression many times in prehistory, appearing in wet cycles and disappearing during drought. Animals came here to water, as did the toolmakers who pursued them. Ongoing digs now confirm that from 992,000 to 493,000 years ago, the lake’s shore was inhabited by early humans. No actual hominid remains were found there until 2003, when archaeologists from the Smithsonian Institution and the National Museums of Kenya uncovered a single small skull, probably of Homo erectus, a predecessor of our own species.

What had been found, however, were thousands of stone hand-axes and cleavers. The most recent were designed for throwing: rounded on one end, with a point or double-faced edge on the other. Where protohumans at Olduvai Gorge, like Australopithecus, simply banged stones together until one chipped, these were flaked with techniques that could be duplicated, rock after rock. They are in every layer of human habitation here, meaning that people hunted and butchered game around Olorgesailie for at least half a million years.

Recorded history from civilization’s Fertile Crescent beginnings to the present day has taken barely more than th of the time that our ancestors lived in this one spot, grubbing plants and heaving sharpened stones at animals. There must have been a lot of prey to feed a growing predator population with awakening technological skill. Olorgesailie is cluttered with femurs and tibia, many smashed for their marrow. The quantities of stone tools surrounding the impressive remains of an elephant, a hippo, and an entire flock of baboons, suggest that the entire hominid community teamed up to kill, dismember, and devour their quarry.

Yet how is this possible if in less than a millennium human beings decimated America’s supposedly richer Pleistocene megafauna? Surely Africa had even more people, and for a lot longer. If so, why does Africa still have its famous big-game menagerie? The flaked basalt, obsidian, and quartzite blades at Olorgesailie show that for a million years hominids could cut even an elephant’s or a rhino’s thick hide. Why aren’t Africa’s big mammals extinct as well?

Because here, humans and megafauna evolved together. Unlike the unsuspecting American, Australian, Polynesian, and Caribbean herbivores who had no inkling of how dangerous we were when we unexpectedly arrived, African animals had the chance to adjust as our presence increased. Animals growing up with predators learn to be wary of them, and they evolve ways to elude them. With so many hungry neighbors, African fauna have learned that massing in large flocks makes it harder for predators to isolate and catch a single animal, and assures that some are available to scout for danger while others feed. A zebra’s stripes help it befuddle lions by getting lost in a crowded optical illusion. Zebras, wildebeest, and ostriches have forged a triple alliance on open savannas to combine the excellent ears of the first, the acute sense of smell of the second, and the sharp eyes of the third.

If these defenses worked every time, of course, the predators would go extinct. An equilibrium emerges: in a short sprint, the cheetah gets the gazelle; in a longer race, gazelles outlast the cheetah. The trick is to avoid becoming someone else’s dinner long enough to breed replacements, or to breed often enough to insure that some replacements always survive. As a result, carnivores like lions often end up harvesting the sickest, oldest, and weakest. That was what early humans did as well—or, like hyenas, at first we probably did something even easier: we ate the carrion left by some more adept hunter.

Equilibrium dissolves, however, when something changes. The genus Homo’s burgeoning brain spawned inventions that challenged herbivore defense strategies: tight flocks, for example, increased the odds that a thrown hand-axe would actually connect with a target. Many species found in Olorgesailie sediments, in fact, are now extinct, including a horned giraffe, a giant baboon, an elephant with down-curved tusks, and a hippopotamus even beefier than today’s. It isn’t clear, however, that humans drove them to extinction.

This, after all, was the mid-Pleistocene—a time when 17 ice ages and their interregna yanked global temperatures up and down and alternately soaked or parched any land that wasn’t frozen solid. The Earth’s crust squeezed and relaxed under the shifting weight of ice. The Eastern African Rift widened and volcanoes blew, including one that periodically bombed Olorgesailie with ashes. After two decades of studying Olorgesailie’s strata, Smithsonian archaeologist Rick Potts began to notice that certain persistent species of plants and animals typically survived periods of climatic and geologic upheaval.

One of these was us. At Lake Turkana, a Rift lake shared by Kenya and Ethiopia, Potts tallied a rich trove of our ancestors’ remains and realized that whenever climate and environmental conditions grew unruly, early species of Homo outnumbered, and finally displaced, even earlier hominids. Adaptability is the key to who is fittest, one species’ extinction being another’s evolution. In Africa, megafauna fortunately evolved their own adaptable forms right along with us.

That is fortunate for us, too, because to picture how the world was before us—as our basis for understanding how the world may evolve after us—Africa is our most complete bank of living genetic heritage, filled with entire families and orders of animals that were sacked elsewhere. Some actually are from elsewhere: when North Americans stand in the open sunroof of a safari jeep in the Serengeti, stunned by the vastness of a herd of zebras, they’re seeing descendants of American species that herd over Asian and Greenland-European land bridges, but are now lost to their own continent. (That is, until Columbus reintroduced Equus after a hiatus of 12,500 years; before that, some horse species that flourished in America were probably also striped.)

If Africa’s animals evolved learning to avoid human predators, how would the balance swing with humans gone? Are any of its megafauna so adapted to us that some subtle dependence or even symbiosis would be lost along with the human race, in a world without us?

The high, cold Aberdares moors in central Kenya have discouraged human settlers, though people must have always made pilgrimages to this source. Four rivers are born here, heading in four directions to water Africa below, plunging along the way from basalt overhangs into deep ravines. One of these waterfalls, the Gura, arcs through nearly 1,000 feet of mountain air before being swallowed by mist and tree-sized ferns.

In a land of megafauna, this is an alpine moor of megaflora. Except for a few pockets of rosewood, it is above the tree line, occupying a long saddle between two 13,000-foot peaks that form part of the Rift Valley’s eastern wall, just below the equator. Treeless—yet giant heather rises 60 feet here, dripping curtains of lichen. Groundcover lobelia turns into columns eight feet high, and even groundsel, usually just a weed, mutates into 30-foot trunks with cabbage tops, growing amid massive grass tussocks.

Small wonder that the descendants of early Homo who climbed out of the Rift and eventually became Kenya’s highland Kikuyu tribe figured that this was where Ngai—God—lived. Beyond the wind in the sedges and the tweep of wagtails, it’s sacredly quiet. Rills lined with yellow asters flow soundlessly across spongy, hummocked meadows, so rain-logged that streams appear to float. Eland—Africa’s biggest antelopes, seven feet tall and 1,500 pounds, their helix horns a yard long, their numbers dwindling—seek refuge at these freezing heights. The moor is too high for most game, though, except for waterbucks and hidden lions who await them in fern forests along the plunge pools.

At times elephants appear, babies following a big tusker as she stomps through purple clover and smashes giant thickets of St. John’s wort in pursuit of her daily 400 pounds of forage. Fifty miles east of Aberdares, across a flat valley, elephants have been spotted near the snow line of Mount Kenya’s 17,000-foot spire. Far more adaptable than their late woolly mammoth cousins, individual African elephants once could be tracked by trails of dung leading from Mount Kenya or the cold Aberdares down to Kenya’s Samburo desert, an elevation drop of two miles. Today, the din of humanity interrupts the corridors linking those three habitats. The elephant populations of Aberdares, Mount Kenya, and Samburo have not seen each other for decades.

Below the moor, a 1,000-foot band of bamboo circles the Aberdares Mountains, sanctuary to the nearly extinct bongo, another of Africa’s striped camouflagees. In bamboo so dense it discourages hyenas and even pythons, the spiral-horned bongo’s only predator is unique to the Aberdares: the seldom-seen melanistic, or black, leopard. The brooding Aberdares rain forest is also home to a black serval and a black race of the African golden cat.

It’s one of the wildest places left in Kenya, with camphor, cedar, and croton trees so thick with lianas and orchids that 12,000-pound elephants easily hide here. So does the most imperiled of all African species: the black rhino. About 400 remain in Kenya, down from 20,000 in 1970, the rest poached for horns that bring $25,000 each in the Orient for alleged medicinal properties, and in Yemen for use as ceremonial dagger handles. The estimated 70 Aberdares black rhinos are the only ones in their original wild habitat.

Humans once hid here, too. During colonial times, the well-watered, volcanic Aberdares slopes belonged to British tea and coffee growers who alternated their plantations with sheep and cattle ranches. The agricultural Kikuyu were reduced to sharecropping plots called shambas on their now-conquered land. In 1953, under the cover of the Aberdares forest, they organized. Surviving on wild figs and the brown speckled trout stocked by the British in Aberdares streams, Kikuyu guerrillas terrorized white landowners in what became known as the Mau Mau Rebellion. The Crown brought divisions from England and bombed the Aberdares and Mount Kenya. Thousands of Kenyans were killed or hung. Barely 100 British died, but by 1963 a negotiated truce had inexorably led to majority rule, which became known in Kenya as uhuru—independence.

Today, the Aberdares is an example of that wobbly kind of pact that we humans have struck with the rest of nature known as a national park. It is haven to rare giant forest hogs and the smallest antelopes—jackrabbit-sized suni—and to golden-winged sunbirds, silvery-cheeked hornbills, and incredible scarlet-and-beyond-blue Hartlaub’s turacos. The black-and-white colobus monkey, whose bearded visage surely shares genes with Buddhist monks, dwells in this primal forest, which sweeps in all directions down the slopes of the Aberdares . . .

. . . until it stops at an electric fence. Two hundred kilometers of galvanized wire, pulsing 6,000 volts, now encircle Kenya’s greatest water catchment. Electrified mesh rises seven feet above ground and is buried three feet beneath it, its posts hot-wired to keep baboons, vervet monkeys, and ringed-tailed civets off them. Where it crosses a road, electrified arches allow vehicles to pass, but dangling live wires deter vehicle-sized elephants from doing the same.

It is a fence to protect animals and people from each other. On either side lies some of the best soil in Africa, planted in forest above and in corn, beans, leeks, cabbage, tobacco, and tea below. For years, incursions went in both directions. Elephants, rhinos, and monkeys invaded and uprooted fields by night. Burgeoning Kikuyu populations snuck farther up the mountain, felling 300-year-old cedars and podoconifers as they advanced. By 2000, nearly one-third of the Aberdares was cleared. Something had to be done to keep trees locked in place, to keep enough water transpiring through leaves and raining back into Aberdares rivers, to keep them flowing to thirsty cities like Nairobi, and to keep hydroelectric turbines spinning and Rift lakes from disappearing.

Hence, the world’s longest electric barricade. By then, however, the Aberdares had other water problems. In the 1990s, a deep new drain had opened at its skirts, cloaked innocently in roses and carnations, as Kenya passed Israel to become Europe’s biggest provider of cut flowers, which now exceed coffee as its main source of export income. This fragrant turn of fortune, however, incurs a debt that may keep compounding long after flower lovers are no longer around.

A flower, like a human, is two-thirds water. The amount of water a typical floral exporter therefore ships to Europe each year equals the annual needs of a town of 20,000 people. During droughts, flower factories with production quotas stick siphons into Lake Naivasha, a papyrus-lined, freshwater bird and hippo sanctuary just downstream from the Aberdares. Along with water, they suck up entire generations of fish eggs. What trickles back whiffs of the chemical trade-off that keeps the bloom on a rose flawless all the way to Paris.

Lake Naivasha, however, doesn’t look quite so alluring. Phosphates and nitrates leached from flower greenhouses have spread mats of oxygen-choking water hyacinth across its surface. As the lake level drops, water hyacinth—a South American perennial that invaded Africa as a potted plant—crawls ashore, beating back the papyrus. The rotting tissues of hippo carcasses reveal the secret to perfect bouquets: DDT and, 40 times more toxic, Dieldrin—pesticides banned in countries whose markets have made Kenya the world’s number-one rose exporter. Long after humans and even animals or roses go, Dieldrin, an ingeniously stable, manufactured molecule, may still be around.

No fence, not even one packing 6,000 volts, can ultimately contain the animals of the Aberdares. Their populations will either burst the barriers or wither as their gene pools shrink, until a single virus snuffs an entire species. If humans are snuffed first, however, the fence will stop dispensing jolts. Baboons and elephants will make an afternoon fete of the grains and vegetables in the surrounding Kiyuku shambas. Only coffee stands a chance to survive; wildlife don’t crave caffeine very much, and the arabica strains brought long ago from Ethiopia liked central Kenya’s volcanic soils so much they’ve gone native.

Wind will shred the polyethylene greenhouse covers, their polymers embrittled by equatorial ultraviolet rays whose potency is abetted by the flower industry’s favorite fumigant, methyl bromide, the most potent ozone destroyer of all. The roses and carnations, addicted to chemicals, will starve, although water hyacinth may outlast everything. The Aberdares forest will pour through the deactivated fence, repossessing shambas and overrunning an old colonial relic below, the Aberdares Country Club, its fairways currently kept trimmed by resident warthogs. Only one thing stands in the forest’s way from reconnecting the wildlife corridors up to Mount Kenya and down to the Samburo desert: a ghost of the British Empire, in the form of eucalyptus groves.

Among the myriad species loosed on the world by humans that have surged beyond control, eucalyptus joins ailanthus and kudzu as encroachers that will bedevil the land long after we’ve departed. To power steam locomotives, the British often replaced slow-maturing tropical hardwood forests with fast-growing eucalyptus from their Australian Crown colonies. The aromatic eucalyptus oils that we use to make cough medicine and to disinfect household surfaces kill germs because in larger doses they’re toxins, meant to chase off competitive plants. Few insects will live around eucalyptus, and with little to eat, few birds nest among them.

Lusty drinkers, eucalypti go wherever there’s water, such as along shamba irrigation ditches, where they’ve formed tall hedgerows. Without people, they’ll aim to colonize deserted fields, and they’ll have a head start on the native seeds blowing down the mountain. In the end, it may take a great natural African lumberjack, the elephant, to blaze a trail back to Mount Kenya and expel the last British spirits from the land for good.

2. Africa After Us

In an Africa without humans, as elephants push above the equator through Samburo and then beyond the Sahel, they may find a Sahara Desert in northward retreat, as desertification’s advance troops—goats—become lunch for lions. Or, they may collide with it, as temperatures rising on a wave of a human legacy, elevated atmospheric carbon, quicken its march. That the Sahara has lately advanced so rapidly and alarmingly—in places, two to three miles per year—owes to unfortunate timing.

Only 6,000 years ago, what is now the world’s largest nonpolar desert was green savanna. Crocodiles and hippos wallowed in plentiful Sahara streams. Then Earth’s orbit underwent one of its periodic readjustments. Our tilted axis straightened not even half a degree, but enough to nudge rain clouds around. That alone was not sufficient to turn grasslands to sand dunes. But the coincidence of human progress tipped what was becoming an arid shrubland over a climatic edge. During two previous millennia, in North Africa, Homo sapiens had gone from hunting with spears to growing Middle Eastern grains and raising livestock. They mounted their belongings, and themselves, on newly tamed descendants of an American ungulate that luckily emigrated before its cousins back home perished in a megafaunal holocaust: the camel.

Camels eat grass; grass needs water. So did their masters’ crops, whose bounty begat a population boom of humans. More humans needed more herds, pasture, fields, and more water—all at just the wrong time. No one could have known that the rains had shifted. So people and their flocks ranged farther and grazed harder, assuming that the weather would return to what it had been, and that everything would grow back the way it was.

It didn’t. The more they consumed, the less moisture transpired skyward and the less it rained. The result was the hot Sahara we see today. Only it used to be smaller: Over this past century, the numbers of Africa’s humans and their animals have been rising, and now temperatures are, too. This leaves the precarious sub-Saharan tier of Sahel countries at the brink of sliding into the sand.

Farther south, equatorial Africans have herded animals for several thousand years and hunted them even longer, yet between wildlife and humans there was actually mutual benefit: As pastoralists such as Kenya’s Maasai shepherded cattle among pastures and water holes, their spears ready to discourage lions, wildebeest tagged along to take advantage of the predator protection. They, in turn, were followed by their zebra companions. The nomads economized by eating meat sparingly, learning to live on their flocks’ milk and blood, which they drew by carefully tapping and staunching their cattle’s jugular veins. Only when drought reduced fodder for their herds did they fall back on hunting, or trade with bushmen tribes that still lived off game.

This balance among humans, flora, and fauna first began to shift when humans became prey themselves—or rather, commodities. Like our kin the chimpanzees, we’d always murdered one another over territory and mates. But with the rise of slavery, we were reduced to something new: an export crop.

The mark that slavery left on Africa can be seen today in southeastern Kenya, in brushy country known as Tsavo, an eerie landscape of lava-flows, flat-topped tortilis acacias, myrrh, and baobab trees. Because Tsavo’s tsetse flies discouraged cattle herding, it remained a hunting ground for Waata bushmen. Their game included elephant, giraffe, cape buffalo, assorted gazelles, klipspringer, and another striped antelope: the kudu, its horns corkscrewing for an amazing six feet.

The destination for black slaves in East Africa was not America, but Arabia. Until the mid-19th century, Mombasa, on Kenya’s coast, was the shipping port for human flesh, the end of a long line for Arab slavers who captured their merchandise at gunpoint in central African villages. Caravans of slaves marched barefoot down from the Rift, herded by armed captors mounted on donkeys. As they descended into Tsavo, the heat rose and tsetse flies swarmed. Slavers, shooters, and whichever prisoners had survived the journey made for a fig-shaded oasis, Mzima Springs. Its artesian pools, filled with terrapins and hippopotamuses, were refreshed daily by 50 million gallons of water upwelling from porous volcanic hills 30 miles away. For days slave caravans paused here, paying Waata bow-hunters to replenish their stores. The slave route was also the ivory route, and every elephant encountered was harvested. As demand for ivory grew, its price outstripped that of slaves, who became chiefly valued as ivory porters.

Near Mzima Springs, the water outcropped again, forming the Tsavo River, which eventually led to the sea. With shady groves of fever trees and palms, this route was irresistible, but the price was often malaria. Jackals and hyenas followed the caravans, and Tsavo’s lions developed reputations as maneaters by dining on dying slaves left behind.

Until the late 19th century, when the British ended slavery, thousands of elephants and humans perished along the ivory-slave route between the central plains and Mombasa’s auction block. As the slave trail closed, construction commenced on a railroad between Mombasa and Lake Victoria, a source of the Nile, critical to British colonial control. Tsavo’s hungry lions gained international fame for devouring railway workers, sometimes leaping aboard trains to corner them. Their appetites became the stuff of legend and movies, which usually failed to mention that their hunger owed to a scarcity of other game, slaughtered to feed a 1,000-year cavalcade of enslaved human cargo.

After slavery and rail construction, Tsavo was an abandoned, empty country. Without people, its wildlife began creeping back. Briefly, so did armed humans. From 1914 to 1918, Britain and Germany, which had previously agreed to carve up much of Africa between them, were fighting a Great War for reasons that seemed even murkier in Africa than in Europe. A battalion of German colonists from Tanganyika—today, Tanzania—blew up the British Mombasa-Victoria railroad on several occasions. The two sides engaged each other amid palms and fever trees along the Tsavo River, living on bush meat and dying of malaria as much as from bullets, but bullets having the usual disastrous repercussions for wildlife.

Again, Tsavo was emptied. Again, in the absence of humans, it filled with animals. Sandpaper trees laden with yellow saucerberries overgrew the World War I battlefields, hosting families of baboons. In 1948, stating that people had no other use for it, the Crown declared Tsavo, one of human history’s busiest trade routes, a wilderness refuge. Two decades later, its elephant population was 45,000—one of Africa’s biggest. That, however, was not to last.

As the white single-engine Cessna takes off, one of the Earth’s most incongruous sights unfolds beneath its wings. The wide savanna below is Nairobi National Park, where elands, Thomson’s gazelles, cape buffalo, hartebeest, ostriches, white-bellied bustards, giraffes, and lions live jammed against a wall of blocky high-rises. Behind that gray urban facade begins one of the world’s largest, poorest slums. Nairobi is only as old as the railroad that needed a depot between Mombasa and Victoria. One of the youngest cities on Earth, it will likely be among the first to go, because even new construction here quickly begins to crumble.

On its opposite end, Nairobi National Park is unfenced. The Cessna passes its unmarked boundary, crossing into a gray plain dotted with morning-glory trees. Through here, the park’s migrating wildebeest, zebra, and rhinos follow seasonal rains along a corridor lately pinched by maize fields, flower farms, eucalyptus plantations, and sprawling new fenced estates with private wells and conspicuous large houses. Together, these may turn Kenya’s oldest national park into yet another wildlife island. The corridor isn’t protected; with real estate outside of roiling Nairobi becoming increasingly attractive, the best option, in the opinion of the Cessna’s pilot, David Western, is for the government to pay owners to let animals cross their property. He’s helped with negotiations, but he’s not hopeful. Everyone fears elephants squashing their gardens, or worse.

Counting elephants is David Western’s project today—something he has done continually for nearly three decades. Raised in Tanzania, son of a British big-game hunter, as a boy he often hiked alongside his gun-toting father for days without seeing another human. The first animal he shot was his last; the look in the dying warthog’s eyes cooled any further passion to hunt. After an elephant fatally gored his father, his mother took her children to the comparative safety of London. David stayed through university studies in zoology, then returned to Africa.

An hour southeast of Nairobi, Kilimanjaro appears, its shrinking snowcap dripping butterscotch under the rising sun. Just before it, verdant swamps burst from a brown alkaline basin, fed by springs from the volcano’s rainy slopes. This is Amboseli, one of Africa’s smallest, richest parks, an obligatory pilgrimage for tourists hoping to photograph elephants silhouetted against Kilimanjaro. That used to be a dry-season event, when wildlife would pack into Amboseli’s marshland oasis to survive on cattails and sedges. Now they’re always here. “Elephants aren’t supposed to be sedentary,” Western mutters as he passes over dozens of females and calves wading not far from a pod of mucking hippos.

From high above, the plain surrounding the park seems infected by giant spores. These are bomas: rings of mud-and-dung huts belonging to Maasai pastoralists, some occupied, some abandoned and melting back into the earth. A defensive ring of stacked, thorny acacia branches encircles each. The bright green patch in every compound’s center is where the nomadic Maasai keep cattle safe from predators at night before moving their herds and families to the next pasture.

As Maasai move out, elephants move in. Since people first brought cattle down from northern Africa after the Sahara dried, a choreography has evolved featuring elephants and livestock. After cattle chew savanna grasses down, woody shrubs invade. Soon they’re tall enough for elephants to munch, using their tusks to strip and eat bark, knocking trees over to reach their tender canopies, clearing the way for grass to return.

As a graduate student, David Western sat atop an Amboseli hill, counting cows led to graze by Maasai herders as elephants plodded in the opposite direction to browse. The census he began here of cattle, elephants, and people has never stopped during his subsequent careers as Amboseli park director, head of the Kenya Wildlife Service, and founder of the nonprofit African Conservation Centre, which works to preserve wildlife habitats by accommodating, not banning, humans who have traditionally shared them.

Dropping to 300 feet, he begins flying wide, clockwise circles, banked at a 30° angle. He tallies a ring of dung-plastered huts—one hut per wife: some wealthy Maasai have as many as 10 wives. He calculates the approximate number of inhabitants, and notes 77 cattle on his vegetation map. What looked from above like blood drops on a green plain turns out to be the Maasai herders themselves: tall, lithe, dark men in traditional red plaid shoulder cloaks—traditional, at least, since the 19th century, when Scottish missionaries distributed tartan blankets that Maasai herdsmen found both warm and light enough to carry as they followed their herds for weeks.

“The pastoralists,” Western shouts over the engine noise, “have become a surrogate migratory species. They behave much like wildebeest.” Like the wildebeest, Maasai herd their cows into short-grass savannas during wet seasons and bring them back to water holes when the rains stop. Over a year, Amboseli’s Maasai live in an average of eight settlements. Such human movement, Western is convinced, has literally landscaped Kenya and Tanzania to the benefit of wildlife.

“They graze their cattle and leave behind woodland for elephants. In time, elephants create grassland again. You get a patchy mosaic of grass, woods, and shrublands. That’s the whole reason for the savanna’s diversity. If you only had woodlands or grasslands, you would only support woodland species or grassland species.”

In 1999, Western described this to paleoecologist Paul Martin, father of the Pleistocene overkill extinction theory, while driving through southern Arizona en route to see where Clovis people finished off local mammoths 13,000 years earlier. Since that time, the American Southwest had evolved without big herbivore browsers. Martin gestured at the tangle of mesquite sprouting on public lands that ranchers leased, which they were always begging permission to burn. “Do you think this could work as elephant habitat?” he asked.

At the time, David Western laughed. But Martin persisted: How would African elephants do in this desert? Would they be able to ascend the craggy granite mountain ranges to find water? Might Asian elephants do better, since they were more closely related to mammoths?

“It’s surely better than using a bulldozer and herbicides to get rid of mesquite,” Western agreed. “Elephants would do it a lot more cheaply and simply, and they also spread manure around for grass seedlings.”

“Exactly,” said Martin, “what mammoths and mastodons did.”

“Sure,” Western replied. “Why not use an ecological surrogate species if you don’t have the original one there?” Ever since, Paul Martin has been campaigning to return elephants to North America.

Unlike Maasai, however, American ranchers aren’t nomads who regularly vacate niches for elephants to use. Increasingly, though, Maasai and their cows are also staying put. The barren, overgrazed ground ringing Amboseli National Park testifies to the result. When light-haired, fair-skinned David Western, of medium height, chats in Swahili with 7-foot, ebony Maasai herdsmen, the contrast dissolves in long-standing mutual regard. Land subdivision has long been their common foe. But with developers and immigrants from rival tribes putting up fences and staking claims, the Maasai have no choice but to seek title and cling to their lands as well. The new human-use pattern reshaping Africa may not be easily obliterated when humans are gone, says Western.

“It’s a bipolar situation. When you force elephants inside a park, and you graze cattle outside, you get two very different habitats. Inside, you lose all your trees, and it becomes grasslands. Outside, it becomes thick bushlands.”

During the 1970s and 1980s, elephants learned the hard way to stay where they’re safe. Unwittingly, they lumbered into a global collision between deepening African poverty, which in Kenya was yoked to the planet’s highest birthrate, and the boom that spawned the so-called Asian economic tigers, which unleashed a craving in the Far East for luxuries. These included ivory; the desire for it outstripped even the lust that once financed centuries of slavery.

As the price, $20 per kilo, rose by a factor of 10, ivory poachers turned places like Tsavo into a trash heap of tuskless carcasses. By the 1980s, more than half of Africa’s 1.3 million elephants were dead. Only 19,000 were left in Kenya, packed into sanctuaries such as Amboseli. International ivory bans and shoot-to-kill orders for poachers calmed but never eradicated the carnage, especially the slaughter of elephants outside parks on the pretext of defending crops or people.

The fever tree acacias that once lined Amboseli’s swamps are now gone, downed by overcrowded pachyderms. As parks become treeless plains, desert creatures like gazelles and oryx replace browsers like giraffes, kudus, and bushbuck. It is a man-made replica of extreme drought, such as Africa knew during ice ages, when habitats shriveled and creatures crammed into oases. Africa’s megafauna made it through those bottlenecks, but David Western fears what may happen to them in this one, stranded on island refuges in a sea of settlements, subdivisions, exhausted pastures, and factory farms. For thousands of years, migratory humans were their escorts across Africa: nomads and their herds taking what they needed and moving on, leaving nature even richer in their wake. But now such human migration is coming to a close. Homo sedentarian has flipped that scenario. Food now migrates to us, along with luxury goods and other consumables that never existed through most of human history.

Unlike anywhere else on Earth—save Antarctica, where people never settled—Africa alone has not suffered a major wildlife extinction. “But intensified agriculture and high human population,” Western worries, “mean that we’re looking at one now.” The balance that evolved between humans and wildlife in Africa has tipped out of control: too many people, too many cows, too many elephants stuffed into too few spaces by too many poachers. The hope that sustains David Western lies in knowing that some of Africa is still as it was, before we evolved into a keystone species potent enough to push even elephants around.

If there were no people left, he believes, Africa, which has been occupied by humans longer than any other place would paradoxically revert to the purest primeval state on Earth. With so much wildlife grazing and browsing, Africa is the only continent where exotic plants haven’t escaped suburban gardens to usurp the countryside. But Africa after people would include some key changes.

Once, North African cattle were wild. “But after thousands of years with humans,” says Western, “they’ve been selected for a gut like an oversized fermentation vat to eat huge amounts of forage during the day, because they can’t graze at night. So now they’re not very quick. Left on their own, they’d be rather vulnerable prime beef.”

And a lot of it. Cattle now account for more than half the live weight of African savanna ecosystems. Without Maasai spears to protect them, they would provide an orgy for binging lions and hyenas. Once cows were gone, there would be more than double the feed for everything else. Shading his eyes, Western leans against his Jeep and calculates what the new numbers would mean. “A million and a half wildebeest can take out grass just as effectively as cattle. You’d see much tighter interaction between them and elephants. They would play the role the Maasai refer to when they say that ‘cattle grow trees, elephants grow grass.’”

As for elephants without people: “Darwin estimated 10 million elephants in Africa. That was actually quite close to what was here before the big ivory trade.” He turns to look at the female herd sloshing in the Amboseli swamp. “At the moment we have half a million.”

No people and 20 times more elephants would restore them as the undisputed keystone species in a patchwork mosaic African landscape. By contrast, in North and South America, for 13,000 years nearly no creatures except insects have eaten tree bark and bushes. After mammoths died, enormous forests would spread unless farmers cleared them, ranchers burned them, peasants cut them for fuel, or developers bulldozed them. Without humans, American forests represent vast niches awaiting any herbivore big enough to extract their woody nutrients.

3. Insidious Epitaph

Partois ole Santian heard the story often when he was growing up, wandering with his father’s cows west of Amboseli. He listens respectfully as Kasi Koonyi, the gray old man living with his three wives in a boma in Maasai Mara, where Santian now works, tells it again.

“In the beginning, when there was only forest, Ngai gave us bushmen to hunt for us. But then the animals moved away, too far to be hunted. The Maasai prayed to Ngai to give us an animal that wouldn’t move away, and He said wait seven days.”

Koonyi takes a hide strap and holds one end of it skyward, to demonstrate a ramp sweeping down to Earth. “Cattle came down from heaven, and everyone said, ‘Look at that! Our god is so kind, he sent us such a beautiful beast. It has milk, beautiful horns, and different colors. Not like wildebeest or buffalo, with only one color.’”

At this point, the story gets sticky. The Maasai claim all the cattle are meant for them, and kick the bushmen out of their bomas. When the bushmen ask Ngai for their own cattle to feed themselves, He refuses, but offers them the bow and arrow. “That’s why they still hunt in the forests instead of herding like we Maasai.”

Koonyi grins, his wide eyes glowing red in afternoon sun that flashes off the pendulous, cone-shaped bronze earrings that stretch his lobes chin-ward. The Maasai, he explains, figured out how to burn trees to create savannas for their herds; the fires also smoked out malarial mosquitoes. Santian gets his drift: When humans were mere hunter-gatherers, we weren’t much different from any other animal. Then we were chosen by God to became pastoralists, with divine dominion over the best animals, and our blessings grew.

The trouble is, Santian also knows, the Maasai didn’t stop there.

Even after white colonials took so much grazing land, nomadic life had still worked. But Maasai men each took at least three wives, and as each wife bore five or six children, she needed about 100 cows to support them. Such numbers were bound to catch up with them. In Santian’s young lifetime, he has seen round bomas become keyhole-shaped as Maasai appended fields of wheat and corn and began to stay in one place to tend them. Once they became agriculturalists, everything began to change.

Partois ole Santian, who grew up in a modernizing Maasai generation with the option of studying, excelled in sciences, learned English and French, and became a naturalist. At 26, he became one of a handful of Africans to earn silver certification from the Kenya Professional Safari Guide Association—the highest level. He found work with an ecotourism lodge in the Kenyan extension of Tanzania’s Serengeti Plain, Maasai Mara, a park combining an animals-only reserve with mixed conservation areas where Maasai, their herds, and wildlife might coexist as they always have. The red oat-grass Maasai Mara plain, dotted with desert date and flat-topped acacias, is still as splendid a savanna as any in Africa. Except that the most predominant animal grazing here is now the cow.

Often, Santian ties leather shoes on his long legs and climbs Kileleoni Hill, the highest point in the Mara. It is still wild enough to find impala carcasses hanging from tree limbs where leopards have stored them. From the top, Santian can look 60 miles south into Tanzania and the immense green-grass sea of the Serengeti. There, honking wildebeest mill in huge June flocks that will soon merge like floodwaters and burst across the border, bounding through rivers that boil with crocodiles awaiting their annual northward migration, with lions and leopards dozing above in the tortilis trees, needing only to roll over to make a kill.

The Serengeti has long been an object of Maasai bitterness: half a million square kilometers from which they were swept away in 1951, for a theme park cleansed of a keystone species, Homo sapiens, to humor Hollywood-bred tourist delusions of Africa as wilderness primeval. But Maasai naturalists like Santian are now grateful for it: the Serengeti, blessed with perfect volcanic soils for grassland, is gene bank to the richest concentration of mammals on Earth, a source from which species might one day radiate and repopulate the rest of the planet, if it comes to that. Huge as it is, however, naturalists worry about how the Serengeti will maintain all those uncountable gazelles, let alone elephants, if everything surrounding it turns into farms and fences.

There isn’t enough rain to change all the savanna into arable farmland. But that hasn’t stopped the Maasai from multiplying. So far married to only one woman, Partois ole Santian decided to stop right there. But Noonkokwa, the childhood girlfriend he wed upon completing his traditional warrior training, was horrified to learn that she might be in this marriage alone, with no female companions.

“I’m a naturalist,” he explained to her. “If all the wildlife habitat disappeared, I’d have to farm.” Before subdividing began, Maasai considered farming beneath the dignity of men chosen by God to pastor cattle. They wouldn’t even break sod to bury someone.

Noonkokwa understood. But she was still a Maasai woman. They compromised at two wives. But she still wanted six children. He was hoping to hold it to four; the second wife, of course, would want some, too.

Only one thing, too terrible to contemplate, might slow all this proliferating before all the animals go extinct. The old man, Koonyi, had said it himself. “The end of the Earth,” he called it. “In time, AIDS will wipe out humans. The animals will take it all back.”

AIDS isn’t yet the nightmare for the Maasai that it has become for sedentary tribes, but Santian saw how it could be soon. Once, Maasai only traveled on foot through savannas with their cows, spear in hand. Now some go to towns, sleep with whores, and spread AIDS on their return. Even worse are the lorry drivers who now show up twice a week, bringing gasoline for the pickups, motor scooters, and tractors that Maasai farmers purchase. Even young uncircumcised girls are getting infected.

In non-Maasai areas, such as up at Lake Victoria, where the Serengeti animals migrate each year, coffee growers too sick with AIDS to groom their plants have turned to growing easy staples like bananas, or cutting trees to make charcoal. Coffee bushes, now feral, are 15 feet high, beyond rehabilitation. Santian has heard people say they don’t care anymore, there’s no cure, so they won’t stop having children. So orphans now live with a virus instead of with parents, in villages where the adults have been all but wiped out.

Houses with no one left alive are collapsing. Mud-stick huts with dung roofs have melted away, leaving only half-finished houses of brick and cement begun by traders with money made from driving their lorries. Then they got sick, and gave their money to herbalists to cure them and their girlfriends. Nobody got well, and construction never resumed. The herbalists got all the money, then got sick themselves. In the end, the traders died, the girlfriends died, the medicine men died, and the money vanished; all that remains are roofless houses with acacias growing in the middle, and infected children who sell themselves to survive until they die early.

“It’s wiping out a generation of future leaders,” Santian had replied to Koonyi that afternoon, but the old Maasai figured that future leaders wouldn’t matter much with animals back in charge.

The sun rolls along the Serengeti Plain, filling the sky with iridescence. As it falls over the edge, blue twilight settles on the savanna. The day’s remaining warmth floats up the side of Kileleoni Hill and dissolves into the dusk. The chilly updraft that follows carries the screech of baboons. Santian pulls his red-and-yellow tartan shuka tighter.

Could AIDS be the animals’ final revenge? If so, Pan troglodytes, our chimpanzee siblings in central Africa’s womb, are accessories to our undoing. The human immunodeficiency virus that infects most people is closely related to a simian strain that chimps carry without getting sick. (The less-common HIV-II is similar to a form carried by rare mangabey monkeys found in Tanzania.) Infection probably spread to humans through bush meat. On encountering the 4 percent of our genes that differ from the genes of our closest primate relations, the virus mutated lethally.

Had moving to the savanna somehow made us biochemically more vulnerable? Santian can identify every mammal, bird, reptile, tree, and spider, and most flowers, visible insects, and medicinal plants in this ecosystem, but some subtle genetic differences escape him—and everyone searching for an AIDS vaccine as well. The answer may be in our brain, since brain size is where humans differ significantly from chimps and bonobos.

Another burst of yakking from the baboon troop drifts up from below. Probably they’re harassing the leopard who hung the impala meat. Interesting how male baboons vying for alpha status have learned to maintain a truce long enough to cooperate in discouraging leopards. Baboons also have the largest brain of any primate after Homo sapiens, and are the only other primate that adapted to living in savannas as forest habitats shrank.

If the dominant ungulates of the savanna—cattle—disappear, wildebeest will expand to take their place. If humans vanish, will baboons move into ours? Has their cranial capacity lay suppressed during the Holocene because we got the jump on them, being first out of the trees? With us no longer in their way, will their mental potential surge to the occasion and push them into a sudden, punctuated evolutionary scramble into every cranny of our vacant niche?

Santian rises and stretches. A new moon rocks toward the equatorial horizon, its points curving upward like a bowl for silvery Venus to settle inside. The Southern Cross and Milky Way assume their places. The air smells like violets. Up here, Santian hears wood owls, like those he knew in his boyhood until the forests around their bomas turned to wheat fields. If human crops revert to a mosaic of woods and grassland, and if baboons fill our keystone slot, would they be satisfied to dwell in pure natural beauty?

Or would curiosity and sheer narcissistic delight in their unfolding powers eventually push them and their planet to the brink, too?