Brain chips that enable us to control machines with our thoughts. Kidneys and lungs built to order in the lab. Pills to make you smarter and more creative. An implant that gives you a tan and protects against skin cancer. All these innovations are in development; some are already being tested on human subjects.

The next technological frontier will be our own bodies. Genetics, materials science, tissue engineering and nanotechnology are already yielding products to help the sick and injured, including a Band-Aid-like heart patch and the C-leg prosthesis for amputees.

A fetus lives in a world of bubbles. In its earliest days, it’s shaped like one. Later, it floats in one—the squishy, enveloping amniotic sac. And eventually, if all goes well, the fetus releases one bubble of fluid, then another and another, like smoke signals, as it puckers and swallows and floats in the womb. It