In their last epic battle with the demons that were devouring the world, the gods of old sent streams of fire down from the Himalayas. The goddess Durga emerged from that fire, and Kali sprang from her brow and triumphed over the demons. Down through the centuries, around a stone image of Kali at an out-of-the-way jungle temple on the banks of a branch of the holy Ganges, a warren of shrines arose. The place came to be called Kalighat. The fetid and splendid city of Calcutta rose up around it, and Calcutta grew to become British India's imperial capital. Then the great river changed its course, and Kalighat was left to fester on the banks of the scum-covered Tollynalla Canal. There was a dead dog floating in it the first day I visited.…

Among Kali's devotees, an organization known as Shiv Sena finds its most ardent recruits. In the 1980s, Shiv Sena was an irrelevant, obscure, off-the-deep-end relic from the Hindu-Muslim convulsions that followed India's partition, after independence. Twenty years later, Shiv Sena pretty much ran Bombay. Its thugs had come to control political life over a great swathe of the Indian subcontinent. The rise of Shiv Sena was one of those things nobody saw coming. It was like the changed world after September 11, 2001, the sudden disappearance of all those ancient and venerable food crops, and the talk about reviving the Tasmanian wolf from DNA extracted from a fetus in a pickle jar. So much is uncertain in the world, but one thing we can say with some certainty is that we are living in an age when we will at last discover the answer to the question that has haunted philosophers from time out of mind. It's the question about whether humanity is capable of determining its own destiny. We should know that by about 2030, they say. Certainly not much later.…

To find some parallel with the conditions of recklessness and excess that prevail in the world, you have to scour such times as 19th-century Ireland in the days before the famine, or reach all the way back to the final days of the Sumerian, Roman, and Mayan empires. You have to look at those desperate moments in human history, the moments just before everything falls apart. You can also look ahead, and try to imagine where all this is leading. You can look at those United Nations Environment Programme Global Outlook scenarios again.…

The big question facing humanity is not whether human beings will survive as a species. In the course of writing this book, I found no convincing evidence to support the popular contention that human behaviour is leading to our inevitable extinction. Even the worst scenarios of ecosystem loss, deforestation, species extinctions, global warming, and crop monoculture would not inevitably result in the extinction of humanity. We are an amazingly resilient species. The way American writer David Quammen puts it, we are a "weedy" species, like cockroaches and pigeons, and we are creating a planet fit only for weeds. But we are also Copernicus and Galileo. We are like cougars. We have figured out ways to colonize every ecological niche on earth. We will survive. So there's hope.

The choice is about how we will survive, and what kind of a planet we want for ourselves and for other living things. It is no longer good enough to talk about letting nature take its own course.

Humanity faces serious decisions, and serious decisions require that we believe in things, and believe deeply. Like humanity's love of living things and the way our brains are patterned for storytelling, our need to believe is ancient and abiding. Deep conviction, faith, ideology, religious devotion-all these things are fundamental, structural components of human nature. We have evolved that way; natural selection has favoured this capacity in us. We can sneer at the market fundamentalists of the world, despise the fascists terrorizing the Islamic part of it, and laugh at the pilgrims in their harmless devotions at Kalighat, but the one thing that has always moved people in times of great peril-the one thing that has allowed broad masses of people to determine their destiny-is the human capacity to believe in things.…

E.?O. Wilson, the "father of biodiversity" and one of the greatest minds of the 20th century, has an idea about how the struggle for belief will unfold in the coming years. "The choice between transcendentalism and empiricism will be the coming century's version of the struggle for men's souls," he says. But the strongest beliefs derive from self-evident truths of the kind that reconcile the traditions of transcendentalism and empiricism. And there is a truth about extinctions, a thing that we all know to be true, somehow, to the very core of our being. In the way the poet William Blake put it, "Everything that lives is holy." You can speak those words with fire in the belly, or you can express them in a perfectly rational and secular manner. In United Nations Resolution A-RES-37-7, the World Charter for Nature, adopted October 28, 1982, the words appear this way: Every form of life is unique, warranting respect regardless of its worth to man, and, to accord other organisms such recognition, man must be guided by a moral code of action.

There have always been ways of saying this, in every language and culture on earth. You certainly don't need to rely solely on the lexicon of environmentalism to justify that ancient desire that persists in all of us to be in a living, breathing world, rich in the diversity and abundance of life. It is our right, and we should claim it, and humanity actually is capable of determining its own destiny. We certainly should not test that proposition by waiting to see if the ship sinks.

We should take the helm. We should reclaim the rights and entitlements of citizenship that have been stripped away from so much of the world. We can expand the scope of democracy, everywhere, and in ways that will allow us to confront the forces behind monoculture, ecological collapse, and all those other things that always seem to lead to a field where people make the sign of the cross when they pass. The work will require great sacrifice, discipline, and violence. We cannot shy away from the moral duty of that work because of a fear of those things. It will be hard work. It is certainly not the sort of thing you would want to leave to environmentalists.

Humanity has already had some brief moments at the helm, and they were exhilarating. In 1948, the founding member states of the United Nations drafted the Universal Declaration of Human Rights. That is something worth building upon, especially in a world faced with increasingly difficult questions about the protection of cultural diversity. When a great hole in the earth's paper-thin ozone layer was being ripped open by chlorofluorocarbons and halons, a handful of the world's nations signed on to a series of covenants to phase out those lethal substances, culminating in the Montreal protocol in 1997. By 2002, 183 nations had signed on. The United Nations' Kyoto protocol on climate change was an embarrassing baby step in the direction of addressing greenhouse-gas emissions, and the United States was allowed to get away with ignoring it. But people will only put up with so much. That's another conclusion I'd reached by the time I'd reached Kalighat. There's always a tipping point. It's just hard to predict when or where that happens, or upon whose back the last straw breaks.

The last thing I learned is a way to answer that question, "What, then, do we do?" It is this: You do what you can.

If it's some great insight you're after, all I can say is that the great insights lie only in the rich variety of humanity's stories, the specific and the particular stories, and the great multiplicity and diversity of our ideas. Our best hopes lie in strengthening the conditions that allow the flourishing of a diversity of living things, a diversity of ideas, and a diversity of choices.

Extinction is the thing that destroys those very conditions, so you join the epic battle with the demons that are devouring the world, and you do what you can. It's all anyone can expect of you. You do everything you can.