Meanwhile, the Indian elephant seemingly only hung on in regions where they were useful as beasts of burden–in India and Sri Lanka, and eastwards into Thailand and elsewhere in Southeast Asia. They were the living tanks of wars that were fought more than two millennia ago, heavy-lifting machinery for foresters and agriculturalists, and warm-blooded trucks and bulldozers for the construction industry. Wild–or, at least, semi-wild–populations continued to exist in part because it was more practical to capture and then train young, wild elephants than to corral bull elephants and breed them in captivity. Today they are surviving better than their African counterparts because they continue to be used for hauling logs in forestry, and they take centre stage in cultural festivals and religious ceremonies, as well as being used as viewing platforms by tourists. But there is an additional reason. Female Indian elephants and some of the males don’t have tusks. They are far less profitable for ivory poachers than their African relations.
Elsewhere, we killed them all, and there are plenty of dead elephants to tell the tale. I even sat next to one, at the Smithsonian Institution’s Botanical Symposium recently. This particular African bush elephant was presiding over a collection of scientists and conservationists enjoying their conference dinner in the National Museum of Natural History in Washington DC. A stuffed vulture soared above, forever fixed in flight, attached by a pole high in the museum’s rotunda. The unmoving, unblinking elephant looked on; the nearby halls were filled with his dead relatives. The massive skeleton of an American mastodon reminded us that a stroll down DC’s National Mall, the green parkland that lies beyond the museum walls, would have been a very different experience in the pre-human past. This particular member of the elephant family had sturdy, curving tusks and a thick coat to survive the cold of North American winters, and they once roamed from where the United States Capitol buildings are situated today to where the Lincoln Memorial now stands, and wallowed in nearby Potomac marsh. This primeval landscape has been replaced by mown grass, planted trees, house sparrows from Asia and North American house finches. Humans from Africa abound where mastodons used to plod.
There must have been twenty or more different kinds of elephants in the world at the time when modern humans began to slaughter them. These included the elephants we recognize today, as well as mammoths, mastodons, gomphotheres and stegodonts, all sharing the characteristics of long, grasping noses and impressive tusks. Only three species survive.4 The bush or savanna elephant would once have inhabited most of the African continent, from the shores of the Mediterranean to the Cape of Good Hope, but they are now virtually confined to parks, game reserves and, paradoxically, hunting reserves, where they are defended from poachers by wire fences and armed guards. The far rarer African forest elephant is in even worse shape, inhabiting the steamy jungles of the Congo Basin. And the Asian elephants that used to range from close to the Mediterranean Sea to China’s Pacific coast are now confined to a smattering of enclaves from India to Borneo. All three are much diminished, but they are the lucky ones.
Seven-tonne, straight-tusked elephants once lived throughout Europe. Elephants and hippopotami would have inhabited swamps at the northern fringes of Europe’s Adriatic Sea, now replaced by Venice and its collection of Anthropocene success stories: Italian sparrows, feral rock doves and the inevitable rats and mice. Some elephants had become stranded on Mediterranean islands during the ice ages, when water levels were lower, or had swum across, and there they evolved into miniaturized versions of their ancestors. Malta and Sicily had one dwarf species. Cyprus had another that was just a metre high–a real pygmy elephant. If only they had survived, Mediterranean beaches would have been much more exciting for sunbathing tourists.
We can add mammoths to the list, relatives of the Indian elephant. These include the cartoon-classic woolly mammoth of northern Asia and North America, with its shaggy rufous-red fur coat and arching tusks, and the Columbian mammoth, which lived further south in North America and in parts of Central America. Like the European elephants, island-living populations of mammoths were prone to evolve into tiny versions of their continental relatives. One dwarf island species inhabited the Channel Islands off California, with others marooned in the Mediterranean islands of Crete and Sardinia. Meanwhile, fossils of the American mastodon have been found from Honduras to Alaska, and from Florida to California. The rest of the New World, from Mexico to Argentina, was home to at least three, and possibly five, species of ancient gomphotheres. These animals looked slightly less like modern elephants and were characterized by a protruding lower jaw and extended teeth as well as regular tusks and a trunk.
Perhaps the largest of all was the ten-tonne Asian Stegodon, standing four metres at the shoulder, an animal that roamed from Pakistan to Japan, and from China to Indonesia. It is unclear quite how many kinds of Stegodon existed, or which of them were wiped out by humans (in several waves of human colonization out of Africa). At least one widespread mainland species disappeared, and a dwarf Stegodon lived in the company of dwarf humans on the island of Flores, the elephant surviving until about twelve thousand years ago. Other extinct forms have been reported from Japan and the Philippines, as well as from Timor, Sulawesi, and elsewhere among the islands of Indonesia.
This all adds up to at least one elephant species being present over almost the entire land surface of the world, apart from the driest deserts and highest mountains (if we exclude Australia, Antarctica and the oceanic islands, which they were never able to reach). And they were all killed off by humans.5 The ‘natural’ pre-human state of the world is to have elephants virtually everywhere, and it still would be but for the rise of predatory apes.
Just a light touch, and the trigger was released. Thwack. A beam of the densest imaginable wood crashed down, sufficient to immobilize the tapir between two slanting rows of posts that had been lashed together to prevent the animal from escaping to either side. Rows of posts aligned along the foraging trail of a quarter-tonne Brazilian tapir guide the animal towards its demise. If not crushed immediately, it lies helpless until the spear-wielding Guarani hunters return to complete the task. Fortunately, Gabriel, our indigenous Mbyá Guarani guide to the Atlantic forest at Iguazu in Argentina, was not wielding a spear and there was no tapir. He was simply demonstrating how the largest surviving South American mammal could be captured and killed by a single person. He then continued–with relish–to demonstrate an array of other snares and traps, some baited with fruits to attract gamebirds into a crushing wooden guillotine, others cage-traps that could be tailored to drop on their prey and, finally, the device from Hell–attracted to dangling prey, jaguars trigger a release that deposits the luckless cat on to a bed of spikes. My sister Philippa gasped, as she is prone to do. She and my wife, Helen, had come to admire the splendour of Iguazu Falls and instead were receiving instruction in fatal technologies.
But it was a revelation. It was easy to see how, with several people to operate them, scaled-up versions of the same designs could have been used to trap much larger animals, even those the size of an elephant. And the jaguar trap could have impaled now-extinct, sabre-toothed Smilodon cats with little or no alteration–Smilodon was about four times heavier than the jaguar and would have declined in number when its prey disappeared, and as a consequence of direct hunting. These traps would not necessarily have killed the largest animals immediately, but they would have held them long enough for armed hunters to move in and complete the task.
Similar Stone Age technologies would potentially have been available to Gabriel’s ancestors more than ten thousand years ago, when they spread out across the Americas and encountered large animals that had never met a human before. The wooden traps and heavy beams could have been hewn with stone axes. The ropes, tripwires and bow-strings were fashioned from lianas, sinews and woven fibres. Spears were made of fire-hardened wood to finish the struggling animals off, with arrowheads of glassy stones. It was all simple technology, but lethally effective. None of this required Hollywood
visions of muscle-bulging Stone Age hunters locked in mortal combat with fierce beasts. Our planet’s greatest animals were brought down more by ingenuity than by brawn.
Had it not been for Stone Age hunters and trappers, we would today be taking our wildlife safaris in Argentina, where gomphothere elephants were joined by huge ground sloths, as well as car-sized armadillos and hornless, rhino-like toxodons. At Luján near Buenos Aires, thirteen different kinds of mammals averaged over a tonne in weight at a single locality.6 None of them survives. In contrast, the only tonne-sized mammals found on the entire African continent are the two elephants, hippos, white rhinoceros, black rhinoceros and four giraffe species.7 Game viewing in South America would have been far more spectacular, but not unique. Wherever in the world you are reading this book, you would once have been surrounded by an impressive array of staggeringly large animals.
The forests of New Zealand have lost their three-metre-high giant birds, and the outback of Australia no longer has two-tonne marsupials. Madagascar’s vast ‘elephant birds’ and heaviest lemurs are gone. For a trip down memory lane in North America, visit the La Brea tar pits, today surrounded by urban Los Angeles, just a few blocks from Hollywood’s Sunset Boulevard. It is a macabre pre-human animal trap, but a godsend to biologists. Massive ancient animals became stuck in adhesive geological seeps of crude oil and bitumen, and then the predators and scavengers that attended their festering bodies suffered the same fate. The array of unfortunate animals and their predators that have been preserved in the goo reads like fiction: American mastodon, Columbian mammoth, Mexican horse, California tapir, three varieties of ground sloth, American camels, large-headed llamas, over-sized peccaries, enormous short-faced bears, dire wolves, scimitar- and sabre-toothed cats, cheetah-like running cats and American lions. Yet they were real. Alas, the ingenious humans that colonized California over ten thousand years ago were more than a match for them.
These extinctions are almost instantaneous on a geological timescale but slow enough that they are virtually invisible to their perpetrators. Despite its brains, Homo sapiens forgets far more than it remembers. Most cultural knowledge fails to be transmitted for more than a few generations. Small fragments of bone discarded by our ancestors are all that remain to tell us that a deadly combination of human hunters and their kiore rat passengers drove perhaps a thousand bird species extinct from the Pacific Islands in a little over three millennia.9 Haast’s eagle, possibly the largest ever, passed into the New Zealand Maori legends as Te Hokioi and Pouakai, a predatory bird so enormous that it was allegedly capable of escaping with a child in its talons–perhaps it did. But the vast majority slipped from our societal memories. One species of bird was killed off every two or three years in the archipelagos of the Pacific Ocean, but they dropped off the radar, failing to be remembered by today’s society.
The diversity of wild-living large land mammals, the megafauna (megafauna are traditionally defined as species that weigh at least 100 pounds, or 45 kilograms). Current figures (top) show that the largest numbers of heavyweight species survive in Africa. A reconstruction shows that the whole world would have African levels of large beasts if humans had not killed most of them off (bottom).8 A few species of extinct bird were also this heavy (particularly on Madagascar and in New Zealand), but are not included on the maps. Domestic animals are not shown.
Likewise, present-day Europeans are generally oblivious to the absence of rhinoceros and lions in their vineyards, most North American hikers fail to wonder why four-tonne mastodon elephants are missing from the shores of the Great Lakes, and visitors to Yosemite Valley in California are blissfully unaware that three-hundred-kilogram sabre-toothed cats should be stalking their campsites. All these animals would be alive today but for our ancestors. The drip-drip of extinction rarely registers in an individual’s direct experience–who will remember even one hundred years from now that the last individual of Rabbs’ fringe-limbed tree frog passed away on 26 September 2016? We see the state of the Earth as it is, not as it would have been, had humans not existed. Only now is scientific research revealing the magnitude of the changes that took place early in human history.
Our official inventory of human-caused extinction starts in the year 1500. The International Union for the Conservation of Nature (IUCN) has logged the disappearance of around 2 per cent of all mammal species since 1500, as well as 1.6 per cent of bird species, and 2 per cent of amphibians over the same period.10 According to bone and fossil man Tony Barnosky, from the University of California, Berkeley, a further 178 of the world’s largest mammals disappeared long before 1500, and the number could be higher. If we combine these two lists, 5 to 6 per cent of all mammal species have already become extinct in the human era. And these are just the ones we know about. If we add the thousand missing Pacific birds to the IUCN figures, then at least 9 per cent of all the different kinds of birds have already gone, and probably more. These wild species represent a substantial loss of biological diversity, almost entirely caused by humans. This is not yet sufficient to equal one of the so-called ‘Big Five’ mass-extinction events that took place in the geological past, when three-quarters or more of all species became extinct. Taking mammals and birds together, we are ‘only’ about a tenth of the way there. But the rate of extinction is still exceptionally high. We have triggered a ‘mini mass extinction’ and could potentially be on course for a sixth big one if humans continue to dominate the Earth for millennia to come. This would be virtually instantaneous on the schedule of geological time.
This loss is devastating but, luckily, it isn’t the whole story. After every fall during the history of life there has been a subsequent rise in diversity. The survivors of past mass extinctions in our planet’s history formed an unprecedented set of organisms that inherited and diversified in a world different from any that existed before. Consider the last such event, which killed off the dinosaurs when a ten-kilometre-wide asteroid smashed into what is now the Yucatán coast of the Gulf of Mexico.11 The exact sequence and timing of events continue to be disputed, but it is likely that dust clouds generated by the explosion resulted in severe climatic cooling, the widespread death of plants and the proliferation of acid rain for several years, followed by extreme global warming associated with a massive injection of carbon dioxide into the atmosphere, which heated the Earth once the dust settled. Whatever the precise details, the consequence was that three-quarters of the world’s species disappeared, including the dinosaurs.
This explains why the world now contains over ten thousand different kinds of birds and no reptiles weighing more than a tonne, other than a few crocodiles and their relatives. Perhaps because of their feathery insulation and ability to fly away and search out new food supplies, birds were rather better at surviving the huge swings in the Earth’s climate that took place 66 million years ago. We usually think of the rise of the birds and mammals as a tale of diversification after they were released from the burden of having to live with gigantic dinosaurs. And there is an element of truth in this. But for this single, chance event, the La Brea tar pits might be filled with gigantic reptile bones rather than enormous mammals. The absence of dinosaurs was an opportunity for others.
However, a substantial increase in our knowledge of fossils and a revolution in molecular biology is changing this perspective. Birds and mammals did not suddenly appear after the asteroid hit–large numbers of them already existed for millions of years before the dinosaurs took their last breaths.12 They were not simply reclusive creatures scurrying around in the undergrowth hiding from dinosaurs. A time machine trip back 67 million years, a million years before the asteroid hit, would reveal a rather modern-looking set of birds living alongside dinosaurs in forests that were constructed of a wide diversity of quite familiar flowering plants. Just as now, the forests of South America must have resounded with the haunting piping and whistling calls of birds that would have been much like today’s tinamous. These stout-bodied birds generally prefer to walk than fly–tin
amous are relatives of rheas, ostriches and kiwis–and communicate through dense forest using a cacophony of sounds tuned to penetrate the vegetation.
The birds that lived in the air, forests, grasslands and swamps of the late Cretaceous period, 67 million years ago, were recognizably modern birds. For example, birds that would later evolve into pheasants could already be distinguished from proto-ducks and geese. Of course, some groups have shown spectacular levels of diversification since then, particularly the passerines, or perching birds, which picked up the evolutionary pace 30 to 50 million years after the dinosaurs disappeared;13 today’s flycatchers, songbirds, crows and finches are passerines, and they number about half of all bird species that are alive today. Eastern bluebirds, house sparrows, tree sparrows, Spanish sparrows and Italian sparrows belong to this group, too, and they are all quite modern inventions. Still, a considerable diversity of birds was living well before the dinosaur-killing holocaust took place.
The story of the mammals is similar–nearly two-thirds of the history of mammals took place in the presence of dinosaurs. Having originated about 166 million years ago, mammals lived perfectly happily (except when being eaten) alongside large reptiles for 100 million years. The ancestors of today’s egg-laying mammals (platypuses and spiny echidnas), marsupials (including possums and kangaroos) and placentals (most living mammals) had long been separate groups. Some geneticists argue that many different types of placental mammals were already around before the disappearance of the dinosaurs, but a lack of fossils from this time leaves the question unresolved.14 Similar stories hold for other groups of animals. Butterflies in the swallowtail family existed 67 million years ago, and they were already recognizably different from other butterflies. In fact, almost all current families of insects existed long before the end of the Cretaceous period.15 Plant families were even more resilient. Few, if any, major groups of plants died out at this time, even though many individual species disappeared.16
Inheritors of the Earth Page 4
