According to Edward O Wilson, the greatest living Darwinian thinker, the earth is entering a new evolutionary era. We are on the brink of a great extinction the like of which has not been seen since the end of the Mesozoic Era, 65 million years ago, when the dinosaurs disappeared. Species are vanishing at a rate of a hundred to a thousand times faster than they did before the arrival of humans. On current trends, our children will be practically alone in the world. As Wilson has put it, humanity is leaving the Cenozoic, the age of mammals, and entering the Eremozoic - the era of solitude.
The last mass extinction has not yet been fully explained. Many scientists believe it to have been the result of meteorites whose impact suddenly altered the global climate, but no one can be sure. In contrast, the cause of the current mass extinction is not in doubt: human expansion. Homo rapiens is gutting the earth of biodiversity. As humans invade and exploit the last vestiges of wilderness, they destroy or destabilise the habitat of tens of thousands of species of plants, insects and animals.
The lush natural world in which humans evolved is being rapidly transformed into a largely prosthetic environment. Crucially, in any time-span that is humanly relevant, this loss of biodiversity is irreversible. True, life on earth recovered its richness after the last great extinction; but only after about ten million years had passed. Unless something occurs to disrupt the trends that are under way, all future generations of human beings will live in a world that is more impoverished biologically than it has been for aeons.
Given the magnitude of this change, one would expect it to be at the centre of public debate. In fact, it is very little discussed. Organisations such as the World Wildlife Fund press on with their invaluable work, and there are occasional reports of the destruction of wilderness; but for the most part, politics and media debates go on as if nothing is happening. There are many reasons for this peculiar state of affairs, including the ingrained human habit of denying danger until its impact is imminent; but the chief reason is that it has become fashionable to deny the reality of overpopulation.
In truth, the root cause of mass extinction is too many people. As Wilson puts it in his book Consilience: "Population growth can justly be called the monster on the land." Yet according to all the mainstream parties and most environmental organisations, the despoliation of the environment is mainly the result of flaws in human institutions. If we are entering a desolate world, the reason is not that humans have become too numerous. It is because injustice prevents proper use of the earth's resources. There is no such thing as overpopulation.
Interestingly, this view is not accepted in many of the world's poor countries. China, India, Egypt and Iran all have population programmes, as have many other developing nations. Opposition to population control is concentrated in rich parts of the world, notably the US, where the Bush administration pursues a fundamentalist vendetta against international agencies that provide family planning. It is understandable that rich countries should reject the idea of overpopulation. In their use of resources, they are themselves the most overpopulated. Their affluence depends on their appropriating a hugely disproportionate share of the world's non-renewable resources. If they ever face up to that reality, they will have to admit that their affluence is unsustainable.
Another reason for denying the reality of overpopulation is that the growth in human numbers is extremely uneven. In some parts of the world, population is actually declining. This is strikingly true in post-communist Russia. A precipitate fall in public health and living standards has led to a virtually unprecedented population collapse, which is set to accelerate further as an African-style Aids die-off triggered by the country's enormous numbers of intravenous drug users begins to take hold. In other countries, such as Japan, Italy and Spain, declining fertility is leading to zero or negative population growth. Such examples have given currency to the silly notion that overpopulation is no longer an issue - that, if anything, it is a slowdown in the growth of human numbers that we should be worrying about.
But while human numbers are falling in some parts of the world, in others they are exploding. The population of the Gulf states will double in around 20 years - against a background of nearly complete dependency on a single, depleting natural resource. Again, despite China's admirable one-child policy, its population will go on growing for much of this century. Globally, the human population will continue to rise for at least a century - even if worldwide fertility falls to replacement level tomorrow. In 1940, there were around two billion humans on the planet. Today, there are about six billion. Even on conservative projections, there will be nearly eight billion by 2050.
Eight billion people cannot be maintained without desolating the earth. Today, everyone aspires to live after the fashion of the world's affluent minority. That requires worldwide industrialisation - as a result of which the human ecological footprint on the earth will be deeper than it has ever been. If the living standards of rich countries can be replicated worldwide, it is only by making further large inroads into the planetary patrimony of biological wealth.
Rainforests are the last great reservoirs of biodiversity, but they will have to be cleared and turned over to human settlement or food production. What is left of wilderness in the world will be made over to green desert. This is a bleak enough prospect, but what's worse is that it is a path from which there is no turning back. If a human population of this size is to be kept in existence, it must exploit the planet's dwindling resources ever more intensively. In effect, humans will turn the planet into an extension of themselves. When they look about the world, they will find nothing but their own detritus.
There are many who claim to be unfazed by this hideous prospect. Marxists and free-market economists never tire of ridiculing the idea that other living things have intrinsic value. In their view, other species are just means to the satisfaction of human wants, and the earth itself is a site for the realisation of human ambitions. These self-professed rationalists are prone to the conceit that theirs is a purely secular view of the world; but in thinking this way about the relationship of humans to the earth, they are in the grip of a religious dogma. The belief that the earth belongs to humans is a residue of theism. For Christians, humans are unique among animals because they alone are created in the image of God. For the same reason, they are uniquely valuable. It follows that humanity can behave as lord of creation, treating the earth's natural wealth and other animals as tools, mere instruments for the achievement of human purposes.
To my mind, such religious beliefs have caused an immense amount of harm, but at least they are coherent. It is perfectly reasonable to think humans are the only source of value in the scheme of things - so long as you retain the theological framework in which they are held to be categorically different from all other animals. But once you have given up theism, this sort of anthropocentrism makes no sense. Outside the Judaeo-Christian tradition, it is practically unknown. The view of things in which we are separate from the rest of nature and can live with minimal concern for the biosphere is not a conclusion of rational inquiry. It is an inheritance from a single, humanly aberrant religious tradition.
The fashionable belief that there is no such thing as overpopulation is part of an anthropocentric world-view that has nothing to do with science. At the same time, there is more than a hint of anthropocentrism in Wilson's suggestion that we are entering an age of solitude. The idea that, unlike any other animal, humans can take the planet into a new evolutionary era assumes that the earth will patiently submit to their inordinate demands. Yet there is already evidence that human activity is altering the balance of the global climate - and in ways that are unlikely to be comfortable for the human population. The long-term effects of global warming cannot be known with any certainty. But in a worst-case scenario that is being taken increasingly seriously, the greenhouse effect could wipe out densely populated coastal countries such as Bangladesh within the present century, while seriously dislocating food production elsewhere in the world.
The result could be a disaster for billions of people. The idea that we are entering an era of solitude makes sense only if it is assumed that such a world would be stable - and hospitable to humans. Yet we know that the closer an ecosystem comes to being a mono- culture, the more fragile it becomes, as Mark Buchanan demonstrated in the NS two weeks ago ("The extinction of species", 8 July). The world's rainforests are part of the earth's self-regulatory system. As James Lovelock has observed, they sweat to keep us cool. With their disappearance, we will be increasingly at risk. A humanly overcrowded world that has been denuded of much of its biodiversity will be extremely fragile - far more vulnerable to large, destabilising accidents than the complex biosphere we have inherited. Such a world is too delicate to last for long.
There are good reasons for thinking that an era of solitude will not come about at all. Lovelock has written that the human species is now so numerous that it constitutes a serious planetary malady. The earth is suffering from disseminated primatemaia - a plague of people. He sees four possible outcomes of the people plague: "destruction of the invading disease organisms; chronic infection; destruction of the host; or symbiosis, a lasting relationship of mutual benefit to the host and the invader".
The last two can be definitely ruled out. Humankind cannot destroy its planetary host. The earth is much older and stronger than humans will ever be. At the same time, humans will never initiate a relationship of mutually beneficial symbiosis with it. The advance of homo rapiens has always gone with the destruction of other species and ecological devastation. Of the remaining outcomes, the second - in which over-numerous humans colonise the earth at the cost of weakening the biosphere - corresponds most closely to Wilson's bleak vision. But it is the first that is most likely. The present spike in human numbers will not last.
If it is not forestalled by changes in the planet's climate, we can be pretty sure that Wilson's era of solitude will be derailed by the side effects of human strife. Resource scarcity is already emerging as a factor aggravating tension in several regions of the world. In the coming century, it is set to be one of the primary causes of war. A world of eight billion people competing for vital necessities is highly unlikely to be at peace. On the contrary, it is programmed for endemic conflict. New technologies may blunt the edge of scarcity by allowing resources to be extracted and used more efficiently. But their key use will be to secure control over dwindling supplies of oil, natural gas, water and other essential inputs of industrial society.
The internet originated in the military sector. Information technology is at the heart of the revolution in military affairs that is changing the face of war by powering the new generations of computer-guided missiles, unmanned planes and the like. Only a couple of years ago, a host of air-headed publicists was proclaiming the arrival of a weightless world. The reality is just the opposite. The Gulf war was won with computers, and they will be critically important in any attack on Iraq. In that sense, it is true that information technology will be the basis of prosperity in the 21st century. But its main contribution will not be to create a hypermodern, knowledge-driven economy. It will be to enable advanced industrial states to retain control of the most ancient sources of wealth - the world's shrinking supplies of non-renewable resources.
In the past, war has rarely resulted in a long-lasting decline in human numbers. But in a highly globalised world, it could have a new and more devastating impact. With a hugely increased population reliant on far-flung supply networks, large-scale war in the 21st century could do what it has frequently done in the past: trigger food shortages, even famine. Globalisation no more engenders world peace than it guarantees an unending boom. It simply magnifies instability.
As we are now learning, globalisation makes it harder to control the knock-on effects of stock-market crashes. It may not be long before we learn that the same is true of war.
Summing up his view of the future, Wilson writes: "At best, an environmental bottleneck is coming in the 21st century. It will cause the unfolding of a new kind of history driven by environmental change. Or perhaps an unfolding on a global scale of the old kind of history, which saw the collapse of regional civilisations, going back to the earliest in history, in northern Mesopotamia, and subsequently Egypt, then the Mayan and many others scattered across all the inhabited continents except Australia."
Wilson's "new kind of history" would involve a worldwide revolution in attitudes and policies. This would include universal access by women to the means of controlling their fertility, abandonment of the belief that there is a natural right to have as many children as you like, and a basic shift in attitudes to the environment in which it is accepted that our fate and that of the rest of life on earth are inseparably linked. These are the minimum conditions for the new kind of history of which Wilson writes.
Unfortunately, one has only to list these conditions to see that they are unrealisable. There cannot be a sustainable balance between natural resources and human needs so long as the number of people continues to increase, but a growing population can be seen as a weapon. Many Palestinians and Kurds view having large families as a survival strategy. In a world containing many intractable ethnic conflicts, there is unlikely to be a benign demographic transition to a lower birth rate.
The examples we have of societies in which population has declined in the absence of a big social crisis cannot be replicated worldwide. A policy of zero population growth requires universal availability of contraception and abortion, and limits on the freedom to breed; but the authority that could impose these conditions does not exist.
Homo rapiens has a long history of mass killing, but it has rarely chosen to regulate its numbers intelligently and humanely. If population declines, it will be as a result of war, genocide or the kind of generalised social collapse that has taken place in post-communist Russia.
The increase in human population that is currently under way is unprecedented and unsustainable. It cannot be projected into the future. More than likely, it will be cut short by the classical Malthusian forces of "old history". From a human point of view, this is an extremely discomforting prospect; but at least it dispels the nightmare of an age of solitude. The loss of biodiversity is real, and very often irreversible. But we need not fear a world made desolate by human proliferation. We can rely on homo rapiens to spare us that fate.
John Gray is professor of European thought at the London School of Economics and the author of Straw Dogs: thoughts on humans and other animals, to be published by Granta Books in September