As organisms develop, their internal organs arrange in a consistent asymmetrical pattern — heart and stomach to the left, liver and appendix to the right. But how does this happen? Biologists have produced the first evidence that a class of proteins that make up a cell’s skeleton — tubulin proteins — drives asymmetrical patterning across a broad spectrum of species, including plants, nematode worms, frogs, and human cells, at their earliest stages of development.