The alternative way of predicting what is to come is to understand the mechanisms by which we exterminate species. Extinction of species caused by humans may continue accelerating until human population and technology reach a plateau, but neither shows any signs of plateauing. Our population, which grew ten fold from half a billion in 1600 to over five billion now, is still growing at close to two per cent per year. Every day brings new technological advances for changing the earth and its denizens. There are four main mechanisms by which our growing population exterminates species: by overhunting, species introductions, habitat destruction, and ripple effects. Let’s see if these four mechanisms have plateaued.
Overhunting – killing animals faster than they can breed – is the main mechanism by which we have exterminated big animals, from mammoths to California grizzly bears. (The latter appears on the flag of California, the state in which I live, but many of my fellow Californians do not recall that we exterminated our state’s symbol long ago.) Have we already killed off all big animals that we might kill off? Obviously not. While the low numbers of whales led to an international ban on whaling for commercial reasons, Japan thereupon announced its decision to triple the rate at which it kills whales ‘for scientific reasons’. We have all seen photos of the accelerating slaughter of Africa’s elephants and rhinos, for their ivory and horns respectively. At current rates of change, not just elephants and rhinos but most populations of most other large mammals of Africa and Southeast Asia will be extinct outside game parks and zoos in a decade or two.
The second mechanism by which we exterminate is through intentionally or accidentally introducing certain species to parts of the world where they did not previously occur. Familiar examples of introduced species now firmly established in the US are Norway rats, European starlings, boll weevils, and the fungi causing Dutch elm disease and chestnut blight. Europe too has acquired introduced species, of which the misnamed Norway rat is an example (it originated in Asia, not Norway). When species are introduced from one region to another, they often proceed to exterminate some of the new species they encounter, by eating them or causing diseases. The victims evolved in the absence of the introduced pests and never developed defences against them. American chestnut trees have already been virtually exterminated in this way by chestnut blight, an Asian fungus to which Asian chestnut trees are resistant. Similarly, goats and rats have exterminated many plants and birds on oceanic islands.
Have we already spread all possible pests all around the world? Obviously not; there are many islands still free of goats and Norway rats, and many insects and diseases to try to keep out of many countries by quarantines. The US Department of Agriculture has been trying at great expense, but apparently without success, to forestall the arrival of killer bees and Mediterranean fruit flies. In fact, what will probably prove to be the biggest extinction wave caused by an introduced predator in modern times has just started in Africa’s Lake Victoria, home to hundreds of species of remarkable fishes found nowhere else in the world. A large predatory fish called the Nile perch, intentionally introduced in a misguided effort to establish a new fishery, is now eating its way through the lake’s unique fishes.
Habitat destruction is the third means by which we exterminate. Most species occur in just a certain type of habitat: marsh warblers live in marshes, while pine warblers live in pine forests. If one drains marshes or cuts forests, one eliminates the species dependent on those habitats just as certainly as if one were to shoot every individual of the species. For example, when all the forest on Cebu Island in the Philippines was logged, nine of the ten birds unique to Cebu became extinct.
In the case of habitat destruction, the worst is still to come because we are just starting in earnest to destory tropical rainforests, the world’s most species-rich habitats. The rainforests’ biological richness is legendary – over 1,500 beetle species living in a single rainforest tree species in Panama, for instance. Rainforests cover only six per cent of the Earth’s surface but harbour about half of its species. Each area of rainforest has large numbers of species unique to that area. To mention only some exceptionally rich rainforests now being destroyed, the felling of Brazil’s Atlantic forest and Malaysia’s lowland forest is already almost complete, and those of Borneo and the Philippines will be mostly logged within the next two decades. By the middle of the next century, the only large tracts of tropical rainforest likely to be still surviving will be in parts of Zaire and the Amazon Basin.
Every species depends on other species for food and for providing its habitat. Thus, species are connected to each other like branching chains of dominoes. Just as toppling one domino in a chain will topple some others, so too the extermination of one species may lead to the loss of others, which may in turn push still others over the brink. This fourth mechanism of extinction may be described as a ripple effect. Nature consists of so many species, connected to each other in such complex ways, that it is virtually impossible to foresee where the ripple effects from the extinction of any particular species may lead.
For example, fifty years ago no one anticipated that the extinction of big predators (jaguars, pumas, and harpy eagles) on Panama’s Barro Colorado Island would lead to the extinction there of little antbirds, and to massive changes in the tree species composition of the island’s forest. Yet it did so, because the big predators used to eat medium-sized predators like peccaries, monkeys, and coatimundis, and medium-sized seed-eaters like agoutis and pacas. With the disappearance of the big predators, there was a population explosion of the medium-sized predators, which proceeded to eat up the antbirds and their eggs. The medium-sized seed-eaters also exploded in abundance and ate large seeds that had fallen on the ground, thereby suppressing the propagation of tree species producing large seeds and favouring instead the spread of competing tree species with small seeds. That shift in forest tree composition is expected in turn to cause an explosion of mice and rats feeding on small seeds, and then to an explosion in hawks, owls, and ocelots preying on those small rodents. Thus, the extinction of three uncommon species of big predators will have triggered a rippling series of changes in the whole plant and animal community, including the extinction of many other species.
Through these four mechanisms – overhunting, species introductions, habitat destruction, and ripple effects – probably over half of existing species will be extinct or endangered by the middle of the next century, when this year’s crop of human babies reaches the age of sixty. Like many fathers today, I often wonder how I will describe to my twin sons, who are now three years old, the world that I grew up in and that they will never see. By the time they would have been old enough to come with me to New Guinea, one of the world’s biological treasurehouses where I have worked for the past twenty-five years, most of New Guinea’s eastern highlands will be deforested.
When one adds the extinction of species we have already caused to that which we are about to cause, it is clear that the current extinction wave is surpassing the asteroid collision that may have wiped out the dinosaurs. Mammals, plants, and many other types of species survived that collision nearly unscathed, while the current wave is affecting everything from leeches and lilies to lions. Thus, the claimed extinction crisis is neither a hysterical fantasy, nor just a serious risk for the future. Instead, it is an event that has already been accelerating for 50,000 years and will start to approach completion in our children’s lifetimes.
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Let’s finally consider two arguments that accept the reality of the extinction crisis but dismiss its significance. Firstly, is extinction not a natural process anyway? If so, why make a big deal about the wave of extinction happening now?
The answer to this first argument is that the current extinction rate caused by humans is far higher than the natural rate. If the estimate that half the world’s total of thirty million species will become extinct in the next century is correct, then species are now becoming extinct at a rate of about 150,000 per year, or seventeen per
hour. The world’s 9,000 bird species are becoming extinct at a rate of at least two per year, but bird species under natural conditions were disappearing at a rate of less than one per century, so the present rate is at least 200 times the normal rate. Dismissing the extinction crisis on the grounds that extinction is natural would be just like dismissing genocide on the grounds that death is the natural fate of all humans.
The second argument is a simple one: so what? We care about our children, not about beetles and snail darters; who cares if ten million beetle species become extinct? The answer to this argument is equally simple. Like all species, we depend on other species for our existence, in many ways. Some of the most obvious ways are that other species produce the oxygen we breathe, absorb the carbon dioxide we exhale, decompose our sewage, provide our food, maintain the fertility of our soil, and provide our wood and paper.
Then could we not preserve only those particular species that we need, and let other species become extinct? Of course not, because the species we need also depend on other species. Just as Panama’s antbirds could not have anticipated their need for jaguars, the ecological chain of dominoes is much too complex for us to have figured out which dominoes we can dispense with. For instance, could anyone please answer these three questions. Which ten tree species produce most of the world’s paper pulp? For each of those ten tree species, which are the ten bird species that eat most of its insect pests, the ten insect species that pollinate most of its flowers, and the ten animal species that spread most of its seeds? Which other species do these ten birds, insects, and animals depend on? You would have to be able to answer those three impossible questions if you were the president of a timber company trying to figure out which species you could afford to allow to become extinct.
If you are trying to evaluate some proposed development project that would bring in a million dollars but might exterminate a few species, it is still tempting to prefer the certain profit over the uncertain risk. Then consider the following analogy. Suppose someone offers you a million dollars in return for the privilege of painlessly cutting out two ounces of your valuable flesh. You figure that two ounces is only one-thousandth of your body weight, so you will still have nine hundred and ninety-nine thousandths of your body left, which is plenty. That is fine if the two ounces come from your spare body fat and if they will be removed by a skilled surgeon. But what if the surgeon just hacks two ounces from any conveniently accessible part of your body, or does not know which parts are essential? You might then find that the two ounces came from your urethra. If you plan to sell off most of your body, as we now plan to sell off most of our planet’s natural habitats, you are certain eventually to lose your urethra.
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To conclude, let’s place matters in perspective by comparing the two clouds which, as I mentioned at the outset, are hanging over our future. A nuclear holocaust is certain to prove disastrous, but it is not happening now, and it may or may not happen in the future. An environmental holocaust is equally certain to prove disastrous, but it differs in that it is already well underway. It started tens of thousands of years ago, is now causing more damage than ever before, is in fact accelerating, and will climax within about a century if unchecked. The only uncertainties are whether the resulting disaster would strike our children or our grandchildren, and whether we choose to adopt now the many obvious countermeasures.
EPILOGUE
NOTHING LEARNED, AND EVERYTHING FORGOTTEN?
LET’S NOW DRAW together the themes of this book, by tracing our rise over the last three million years, as well as our incipient reversal of all our progress more recently.
The first indications that our ancestors were in any respect unusual among animals were our extremely crude stone tools that began to appear in Africa by around two-and-a-half million years ago. The quantities of tools suggest that they were beginning to play a regular, significant role in our livelihood. Among our closest relatives, in contrast, the pygmy chimpanzee and gorilla do not use tools, while the common chimpanzee occasionally makes some rudimentary ones but hardly depends on them for its existence.
Nevertheless, those crude tools of ours did not trigger any quantum jump in our success as a species. For another million-and-a-half years, we remained confined to Africa. Around a million years ago we did manage to spread to warm areas of Europe and Asia, thereby becoming the most widespread of the three chimpanzee species but still much less widespread than lions. Our tools progressed only at an infinitely slow rate, from extremely crude to very crude. By a hundred thousand years ago, at least the human populations of Europe and western Asia, the Neanderthals, were regularly using fire, but in other respects we continued to rate as just another species of big mammal. We had developed not a trace of art, agriculture, or high technology. It is unknown whether we had developed language, drug addiction, or our strange modern sexual habits and life-cycle, but Neanderthals rarely lived beyond the age of forty and hence may not yet have evolved female menopause.
Clear evidence of a Great Leap Forward in our behaviour appears suddenly in Europe around 40,000 years ago, coincident with the arrival of anatomically modern Homo sapiens from Africa via the Near East. At that point, we began displaying art, technology based on specialized tools, cultural differences from place to place, and cultural innovation with time. This leap in behaviour had undoubtedly been developing outside Europe, but the development must have been rapid, since the anatomically modern Homo sapiens populations living in southern Africa 100,000 years ago were still just glorified chimpanzees, judging by the debris in their cave sites. Whatever caused the leap, it must have involved only a tiny fraction of our genes, because we still differ from chimps in only 1.6% of our genes, and most of that difference had already developed long before our leap in behaviour. The best guess I can make is that the leap was triggered by the perfection of our modern capacity for language.
Although we usually think of the Cro-Magnons as the first bearers of our noblest traits, they also bore the two traits that lie at the root of our current problems: our propensities to murder each other en masse and to destroy our environment. Even before Cro-Magnon times, fossil human skulls punctured by sharp objects and cracked to extract the brains bear witness to murder and cannibalism. The suddenness with which Neanderthals disappeared after Cro-Magnons arrived provides a hint that genocide had now become efficient. Our efficiency at destroying our own resource base is suggested by the extinction of almost all large Australian animals following our colonization of Australia 50,000 years ago, and of some large Eurasian and African mammals as our hunting technology improved. If the seeds of self-destruction have been so closely linked with the rise of advanced civilizations in other solar systems as well, it becomes easy to understand why we have not been visited by any flying saucers.
At the end of the last Ice Age around 10,000 years ago, the pace of our rise quickened. We occupied the Americas, coincident with a mass extinction of big mammals that we may have caused. Agriculture emerged soon thereafter. Some thousands of years later, the first written texts start to document the pace of our technical inventiveness. They also show that we were already addicted to drugs, and that genocide had become routine and admired. Habitat destruction began undermining many societies, and the first Polynesian and Malagasy settlers caused blitzkrieg-like mass exterminations of species. From 1492 AD onwards, the worldwide expansion of literate Europeans lets us trace our rise and fall in detail.
Within the last few decades we have developed the means to send radio signals to other stars, and also to blow ourselves up overnight. Even if we do not blunder into that swift end, our harnessing of much of the Earth’s productivity, our exterminations of species, and our damage to our environment are accelerating at a rate that cannot be sustained for even another century. One might object that, if we look around us, we see no obvious sign that the climax of our history will come soon. In fact, the signs become obvious if one observes and then extrapolates. Starvation, pollution, and destru
ctive technology are increasing; usable farmland, food stocks in the sea, other natural products, and environmental capacity to absorb wastes are decreasing. As more people with more power scramble for fewer resources, something has to give way.
So, what is likely to happen?
There are many grounds for pessimism. Even if every human now alive were to die tomorrow, the damage that we have already inflicted on our environment would ensure that its degradation will continue for decades. Innumerable species already belong to the ‘living dead’, with populations fallen to levels from which they cannot recover, even though not all individuals have died yet. Despite all our past self-destructive behaviour from which we could have learned, many people who should know better dispute the need for limiting our population and continue to assault our environment. Others join that assault for selfish profit or out of ignorance. Even more people are too caught up in the desperate struggle for survival to be able to enjoy the luxury of weighing the consequences of their actions. All these facts suggest that the juggernaut of destruction has already reached unstoppable momentum, that we too are among the living dead, and that our future is as bleak as that of the other two chimpanzees.
This pessimistic view is captured by a cynical sentence that Arthur Wichmann, a Dutch explorer and professor, penned in another context in 1912. Wichmann had devoted a decade of his life to writing a monumental three-volume treatise on the history of New Guinea’s exploration. In 1,198 pages he evaluated every source of information about New Guinea that he could find, from the earliest reports filtering through Indonesia to the great expeditions of the Nineteenth and early Twentieth centuries. He grew disillusioned as he realized that successive explorers committed the same stupidities again and again: they showed the same unwarranted pride in overstated accomplishments, refused to acknowledge disastrous oversights, ignored the experience of previous explorers, repeated previous errors, and hence blundered into unnecessary suffering and death. Looking back on this long history, Wichmann predicted that future explorers would continue to repeat the same errors. The bitter last sentence that concluded Wichmann’s last volume was, ‘Nothing learned, and everything forgotten!’
The Rise and Fall of the Third Chimpanzee Page 42