You were the boy in 1996 who had never spent a night away from home. In fact, you were terrified. And then you met a young man who called himself "Hercules." He liked you, and he wanted you to succeed. Meals were especially hard. It's tough to enjoy spaghetti with tears streaming down your face and your stomach in a knot, so Hercules spent every meal that week with you, eating in a private spot so others wouldn't see you cry. On Tuesday you were ready to give up, but by Friday you had two new things: a friend, and the knowledge that you had made it.

You were the girl in 1989 who was new to your school and painfully shy. Out on a flood plain of the Sandy River, your classmates were noisily searching for life in a necklace of ponds while you stood by, quietly watching them. Chinook, the instructor, noticed this and asked if he could show you "something really cool." You spent the next thirty minutes collecting caddisflies, marveling at how they use tiny pebbles to build themselves a protective shell even as you began to break out of your own. Years later you would take the chance to share something cool with another child.

But this last alternative seems to me to be a special pleading: I am, reluctantly, a self-confessed carbon chauvinist. Carbon is abundant in the Cosmos. It makes marvelously complex molecules, good for life. I am also a water chauvinist. Water makes an ideal solvent system for organic chemistry to work in and stays liquid over a wide range of temperatures. But sometimes I wonder. Could my fondness for materials have something to do with the fact that I am made chiefly of them? Are we carbon- and water-based because those materials were abundant on the Earth at the time of the origin of life? Could life elsewhere—on Mars, say—be built of different stuff?

I am a collection of water, calcium, and organic molecules called Carl Sagan. You are a collection of almost identical molecules with a different collective label. But is that all? Is there nothing in here but molecules? Some people find this idea somehow demeaning to human dignity. For myself, I find it elevating that our universe permits the evolution of molecular machines as intricate and subtle as we.