"Gaia is the entire Earth, and she's come alive, she's been an organic whole, a single creature, for over two billion years now. We can't make complete analogies between Gaia and human beings, or dogs or cats or birds, because until recently we've never studied actual independent organisms. Dogs and cats and birds—and humans— are not independent. We are bits and pieces of Gaia. So is every other living thing on the Earth. Imagine a single cell trying to make analogies between its cytoplasm and organelles, and the role it plays in a human body; it's going to be misled if it compares too rigidly.

"So Gaia, the Earth, is the first independent organism we've studied. I'll call her a 'planetism.' A planetism is made up of plants and animals and microorganisms, and these are made up of cells, or are themselves cells. Cells are made up of cytoplasm and organelles and so on. An organism regulates itself with hormones, neurotransmitters, and it does its work and gets its nutrition with enzymes and other substances . . . all organized, on schedule, synergistic. Self-controlled.

"Gaia does her work with ecosystems. Like any organism, a planetism has a schedule and certain goals to meet. She grows and develops and goes through different stages in her life. Sometimes she undergoes radical shifts, destroying whole ecosystems. Maybe she's experimenting in ways that smaller organisms cannot; she reaches a dead end, clears some of the slate, and starts over. I don't know. But ultimately she has to do what all living things do— mature and reproduce.

"How can a planetism make others like herself? She came into being—probably—without outside interference, though maybe she's the offspring of another planetism. Maybe life was seeded here a long, long time ago. I don't think so, frankly. I think most planetisms have no parents, at least not right now, and so they're free to develop on their own schedule. This takes a long, long time, but eventually she finds a way to reproduce. She develops a reproductive strategy.

"The planetism has found ways to use more and more of her raw materials and surface area. She dominated the oceans, then spread plants and animals out to conquer the barren continents. These plants and animals had somehow become specially suited to life on land. I suspect more than random chance was at work, but I'm too weak to argue about that now. It's irrelevant to my scheme.

' "Now, after ages, humans are here, and we're not doing too badly. We've got an organ as important as the legs on an amphibian—a highly developed brain. Suddenly, Gaia is becoming self-aware, and looking outward. She's developing eyes that can look far into space and begin to understand the environment she has to conquer. She's reaching puberty. Soon she's going to reproduce.