Imagine a Roman in ancient times, standing on a summit, surveying the landscape as he plots the course of a new road. Two thousand years later his roads are still visible as they cross European cities and the countryside, as straight as if drawn by a ruler, deviating only in the face of the most stubborn obstacles. In the 1950s and 1960s, scientists mapped out a similar
sort of route for biology as they described the connections between different types of molecules in the cell.