When Caitlin Cornell looked down her microscope, she saw large bright spots against a black background. They resembled miniature suns, blazing against the backdrop of space. And when Cornell showed the spots to her supervisor, Sarah Keller, a chemist at the University of Washington, “we got really excited,” she recalls. “It was a bit of an ‘Aha!’ moment.” Those spots, she realized, might help address a long-standing puzzle about the origin of life itself.
The cells that make up all living things, despite their endless variations, contain three fundamental elements. There are molecules that encode information and can be copied—DNA and its simpler relative, RNA. There are proteins—workhorse molecules that perform important tasks. And encapsulating them all, there’s a membrane made from fatty acids. Go back far enough in time, before animals and plants and even bacteria existed, and you’d find that the precursor of all life—what scientists call a “protocell”—likely had this same trinity of parts: RNA and proteins, in a membrane. As the physicist Freeman Dyson once said, “Life began with little bags of garbage.”
The bags—the membranes—were crucial. Without something to corral the other molecules, they would all just float away, diffusing into the world and achieving nothing. By concentrating them, membranes transformed an inanimate world of disordered chemicals into one teeming with redwoods and redstarts, elephants and E. coli, humans and hagfish. Life, at its core, is about creating compartments. And that’s much easier and much harder than it might seem.