While studying some of the oldest art in the world found in caves and engraved on animal bones or shells, paleoanthropologist Genevieve von Petzinger has found evidence of a proto-writing system that perhaps developed in Africa and then spread throughout the world.

The research also reveals that modern humans were using two-thirds of these signs when they first settled in Europe, which creates another intriguing possibility. “This does not look like the start-up phase of a brand-new invention,” von Petzinger writes in her recently published book, The First Signs: Unlocking the mysteries of the world’s oldest symbols (Simon and Schuster). In other words, when modern humans first started moving into Europe from Africa, they must have brought a mental dictionary of symbols with them.

That fits well with the discovery of a 70,000-year-old block of ochre etched with cross-hatching in Blombos cave in South Africa. And when von Petzinger looked through archaeology papers for mentions or illustrations of symbols in cave art outside Europe, she found that many of her 32 signs were used around the world. There is even tantalising evidence that an earlier human, Homo erectus, deliberately etched a zigzag on a shell on Java some 500,000 years ago. “The ability of humans to produce a system of signs is clearly not something that starts 40,000 years ago. This capacity goes back at least 100,000 years,” says Francesco d’Errico from the University of Bordeaux, France.

Nonetheless, something quite special seems to have happened in ice age Europe. In various caves, von Petzinger frequently found certain symbols used together. For instance, starting 40,000 years ago, hand stencils are often found alongside dots. Later, between 28,000 and 22,000 years ago, they are joined by thumb stencils and finger fluting — parallel lines created by dragging fingers through soft cave deposits.