Doctors generally consider smallpox to be the worst human disease. It is thought to have killed more people than any other infectious pathogen, including the Black Death of the Middle Ages. Epidemiologists think that smallpox killed roughly one billion people during its last hundred years of activity onearth.

In biology, nothing is clear, everything is too complicated, everything is a mess, and just when you think you understand something, you peel off a layer and find deeper complications beneath. Nature is anything but simple.

It showed a kind of obscenity you see only in nature, an obscenity so extreme that it dissolves imperceptibly into beauty.

Mysteriously, almost unaccountably, my family had ended up in the trees, sort of like the Swiss Family Robinson.

we could eradicate smallpox from nature, but we could not uproot the virus from the human heart

He liked the loneliness of inner space, the sense of being forgotten by the world.

In a sense, the Earth is mounting an immune response against the human species. It is beginning to react to the human parasite, the flooding infection of people, the dead spots of the concrete all over the planet, the cancerous rot-outs in Europe, Japan and the United States, thick with replicating primates, the colonies enlarging and spreading and threatening to shock the biosphere with mass extinctions. Perhaps the biosphere does not 'like' the idea of five billion humans.

The Ludolphian number is fixed in eternity— not a digit out of place, all characters in their proper order, an endless sentence written to the end of the world by the division of the circle’s diameter into its circumference.

The coast redwood is the tallest species of tree on earth. The tallest redwoods today are between 350 and close to 380 feet in height--thirty-five to thirty-eight stories tall. The crown of a tree is its radiant array of limbs and branches, covered with leaves. The crowns of the tallest redwoods can sometimes look like the plume of exhaust from a rocket taking off.

... tree has had a stroke, and its top dies. A redwood can deal with a stroke. It simply grows a new top in a few centuries.

The K-T impact had no evident long-lasting effect on the redwoods. It's possible that, after the impact, the redwoods sprouted up from the remains of their root systems, rising up in fairy rings in a ruined world ...

The coast redwood is a so-called relict species. It is a tiny remnant of a life form that once spread in splendor and power across the face of nature. The redwood has settled down in California to live near the sea, the way many retired people do.