Reading your book, one senses you felt a great urgency to write it?

The urgency was twofold. First, it’s only been within the last decade that a full picture of the crisis in biodiversity has emerged. The second factor was my age. I’m 86. I had a mild stroke a couple of years ago. I thought, “Say this now or never.”

And what I say is that to save biodiversity, we need to set aside about half the earth’s surface as a natural reserve. I’m not suggesting we have one hemisphere for humans and the other for the rest of life. I’m talking about allocating up to one half of the surface of the land and the sea as a preserve for remaining flora and fauna.

In a rapidly developing world, where would such a reserve be?

Large parts of nature are still intact — the Amazon region, the Congo Basin, New Guinea. There are also patches of the industrialized world where nature could be restored and strung together to create corridors for wildlife. In the oceans, we need to stop fishing in the open sea and let life there recover. If we halted those fisheries, marine life would increase rapidly. The oceans are part of that 50 percent.

Now, this proposal does not mean moving anybody out. It means creating something equivalent to the U.N.’s World Heritage sites that could be regarded as the priceless assets of humanity. That’s why I’ve made so bold a step as to offer this maxim: Do no further harm to the rest of life. If we can agree on that, everything else will follow. It’s actually going to be a lot easier than people think.

Why?

Because many problems of human occupancy that we once thought of as insoluble are taking care of themselves. Demographers tell us that the human population could stabilize at about 10 or 11 billion by the end of the century.