I went recently to San Francisco to give a talk to a conference of scientists. The scientists were experts in gathering together mountains of biological data—genome sequences, results of experiments and clinical trials—and figuring out how to make them useful: turning them into new diagnostic tests, for example, or a drug for cancer. The invitation was an honor, but a nerve-wracking one. As a journalist, I had no genome scan to offer the audience.

We science writers do have one ace in the hole, though. Instead of being lashed to a lab bench for years, carrying out experiments to illuminate one particular fold in one particular protein, we get to play the field. We travel between different departments, different universities, different countries, and—most important of all—different disciplines. And sometimes we see links between different kinds of science that scientists themselves have missed. Which is why, when I arrived in San Francisco, walked up to the podium, and switched on my computer, I presented my audience with this photograph of a lake.

For the next hour, I tried to convince them that their bodies are a lot like that lake, and ...