To what extent was fire used as an engineering tool by early modern humans? Kyle Brown and co-authors marshal an impressive array of evidence to show that by 72 000 years ago, and perhaps as far back as 164 000 years ago, prehistoric people prepared the stone from which they planned to make artefacts by intentionally heat-treating it to improve its flaking qualities. This practice is well known from later sites but the increased time depth reported here is remarkable, and contributes to a growing body of evidence that Middle Stone Age people in South Africa were capable of far more sophisticated behaviour than previously realised
