In the 1990s, Colombia reintegrated five left-wing guerrilla groups back into mainstream society after decades of conflict. Education was a big priority – many of the guerrillas had spent their entire lives fighting and were more familiar with the grasp of a gun than a pencil. Reintegration offered them the chance to learn to read and write for the first time in their lives, but it also offered Manuel Carreiras a chance to study what happens in the human brain as we become literate.

Of course, millions of people – children – learn to read every year but this new skill arrives in the context of many others. Their brains grow quickly, they learn at a tremendous pace, and there’s generally