Ruth E. Baker

In the first weeks of an embryo's life, a dense crowd of cells crawls across its body. These cells will later form the facial bones, parts of the heart, and nerves. The crowd doesn't move randomly: a few leader cells take the front, and the rest follow them, like cyclists in a peloton. For a long time, it was believed that leaders are a special breed of cells, born with a drive to lead.

Population growth from a distance looks like a train picking up speed: it crawls at first, then gains momentum. But look closely at the data, and the picture blurs. One measurement shows a dozen individuals, another a hundred. Classical models wipe away this scatter like annoying smudges on a lens. They assume the noise is uniform and simply ignore it.