All this hectic biology occurs under cover of trees, which creates a darkness equally serene and oppressive. When we finally walk out onto an open granite ledge, I am glad for the light.

That night in camp, Mittermeier laments the general ignorance of this terrain. The marine biologist Sylvia Earle made the same point to me some months ago about life in the oceans; we yearn for Mars, a planet as good as dead, and know so little of life on Earth. To date we have identified between 1.5 million and 1.7 million species, but the best guesses put the total number of the planet's species at between 5 million and 15 million, and it could be as high as 100 million. "How can we talk about extinction rates," Mittermeier asks, "unless we know what we're dealing with?"

I ask him why one should not accept the extinction of species as an inevitable natural occurrence. He answers that we are not accepting it; we're inducing it. "I could argue for the economic value of preservation--the biotechnology that leads to the discovery of medicines and so forth," he says. "But if you push me to the wall, I'm for zero deforestation, zero extinction. I believe we have a moral obligation to other species. The only real reason for saving them is that it's right."

Our beds are hammocks tied to posts in a shed with a thatch-and-tarpaulin roof. "If you need to take a leak during the night, watch out for snakes," Mittermeier tells me. "I'll do that," I say, and drink nothing before bedtime. I lie in my hammock draped with white mosquito netting and become a cocoon. I try to sleep but am kept in a semiwaking state by our guides talking softly in Sranan Tongo, a lingua franca mixture of English, Dutch, Portuguese and West African languages, and by the chirping of frogs and birds. Insects make a sound like an endless marimba. There are showers of natural debris--rodents tossing away shells and bits of fruit. I am certain that I hear an animal poking around under my head. Mittermeier confesses that even after all his years of experience, he has never become accustomed to the night sounds.

At 4 a.m. I am fully awakened by the mournful and menacing wail of the howlers--large red monkeys that make a new-day announcement that they are in charge of all the forest's primates. The collective howl begins like a low siren in a fire station, rises to swallow the sky, then ebbs again. It makes you feel alone in the world, like the first human being ever to hear it.

Later, we head back to base camp and go for a swim in the river, where Mittermeier proves that scientists are different from you and me. He remembers to warn me to stay clear of the rocks where electric eels play, but he neglects to mention that piranhas are sharing the water with us. When this finally occurs to him, he adds, "Not to worry. Piranhas only go after open wounds." I hold up my hand with the cut on it. "Oh, yeah," he says.

Except for its lethal possibilities, his distractedness is charming. His mind is simply oriented to the world he has chosen. Nothing makes him happier than looking at it. In the evening he goes out for a while and comes back with two frogs and a toad, in part to show me their characteristics (one is poisonous), but mainly because he is still a kid who likes to go out and get frogs. In the morning, one of our guides spots a parrot high in a tree, a Fransemadam, so called because it spreads a scarlet frill when excited, like the gaudy costume of a French madam. I admire, take note of the bird and am ready to move on, but Mittermeier could stand under the tree for hours lost in the intellectual pleasure of seeing.

Then we are off again, to fly farther south and east to the Maroon Saramaccan village of Asindopo in the region of the Upper Suriname River. Asindopo means "sit down and hope"--a welcome thought to its original settlers, runaway slaves from Dutch plantations in the 18th century. We go by corjal to visit their descendants. Some are swimming; some are washing clothes in the river; some are staring at us. The faces of the children are a cross between innocence and gravity. On a far bank, a glorious ceiba rises to the sky. It is called the "house of the spirits" and is never cut down.