The writer Alan Garner sparks with flint, the stone that, perhaps more than any other, has enabled human civilisation. It's a stone that has featured in some of his novels, such as Red Shift, where the same Neolithic hand axe resurfaces across different times to haunt his characters. And it is time and evolution that he looks at in this essay: "My blood walked out of Africa ninety thousand years ago. We came by flint. Flint makes and kills; gives shelter, food; it clothes us. Flint clears forest. Flint brings fire. With flint we bear the cold."

Alan's essay is the first of five Cornerstones this week in which different writers reflect on how a particular rock shapes both people and place.

Producer: Mark Smalley

Image: Courtesy of the artist Rose Ferraby