What is art? It’s a debate that goes back if not to the dawn of time then certainly to the dawn of modernism, when Picasso and the Cubists shocked the world.

Now the question of whether a three-million-year-old rock can be a work of art has led the British Museum to change the title of an exhibition.

The rock at the centre of the debate is the Makapan Pebble, also known as the Stone of Many Faces. It is believed to have caught the fancy of an ape-like creature, who took it back to the tribal cave. It provides the…