Africa was counting 20,000 years ago. The proof is a bone from Congo

In 1950, a Belgian geologist named Jean de Heinzelin began excavating on the Congolese bank of Lake Edward, near a place called Ishango. Among the finds was a dark bone handle about 10 centimetres long, topped with a fragment of quartz and nearly 20,000 years old.

It looks like very little. A sliver of stone, a stick of bone, some scratches. But the scratches are the reason it now sits in the Royal Belgian Institute of Natural Sciences in Brussels, and the reason mathematicians have argued about it for more than half a century.

A fishing camp by a lake

Ishango lies inside what is now Virunga National Park in North Kivu, Africa's oldest national park. The site was first noticed in 1935 by Hubert Damas, a zoologist from Liège University, who came across human bones and bone harpoon heads while doing a survey and flagged it for a later expedition.

De Heinzelin's team went on to recover thousands of objects. Carbon dating showed that the main layers are between 20,000 and 25,000 years old. The people who lived there fished the lake with hundreds of bone harpoons and barbed points. They were not passing through. They knew their lake, their seasons and their tools.

168 notches in three columns

The handle is unusual on its own: complete prehistoric tools made of two materials are extremely rare. What made it famous is what is carved along it: 168 incisions, regularly spaced and arranged in columns on three sides.

In his 1957 article on the site, de Heinzelin read the groups of lines as numbers, and the patterns he found are striking. According to the museum's own guide to the bone:

• One column holds groups of 11, 13, 17 and 19, which are the four prime numbers between 10 and 20.
• Another holds 11, 21, 19 and 9, which can be read as ten plus one, twenty plus one, twenty minus one and ten minus one.
• The central column pairs numbers with their doubles: three and six, four and eight, five and ten.
• The columns add up to 60, 48 and 60, all multiples of twelve.

What it means, and what it doesn't

Honesty matters here, because it is easy to oversell. Nobody knows for certain what the marks were for. The mathematicians Dirk Huylebrouck and Vladimir Pletser studied de Heinzelin's ideas and concluded the bone may reflect counting in threes and fours, and by extension twelves, but that there is not enough proof that its makers understood prime numbers. The archaeologist Alexander Marshack read it as a record linked to the lunar calendar. The mathematician Olivier Keller warns against projecting our own habit of seeing numbers everywhere onto an ancient object.

Even the careful reading is remarkable. Someone, around 20,000 years ago, sat by an African lake and cut deliberate, ordered marks into a tool they kept. And Ishango is not alone. At Border Cave, in the Lebombo Mountains between South Africa and Eswatini, researchers found a baboon fibula carrying 29 notches made with four different tools, which suggests marks added over time rather than decoration made in one sitting. It is some 42,000 years old. Writing, by comparison, arrived only about 5,000 years ago.

The story we were not told

Most of us learned mathematics as something that came to Africa from elsewhere, carried in textbooks with European names on the theorems. Few of us ever heard the names Ishango or Border Cave at school. Yet some of the oldest known evidence of people keeping count comes from this continent.

That inheritance is being picked up again. The African Institute for Mathematical Sciences was founded in Cape Town in 2003 and has since grown into a network of five centres, in South Africa, Senegal, Ghana, Cameroon and Rwanda. Across the network it counts more than 3,200 alumni, young Africans trained in the mathematical sciences.

Counting is a business skill

There is a plainer lesson here too. Whatever the Ishango marks recorded, they were a way of getting something out of a person's head and onto an object, where it could be checked, compared and passed on.

Every enterprise runs on the same act. A dairy that weighs every delivery knows which farmers supply the best milk. A mill that counts every bag knows where its yield goes. A shop that tracks its stock knows what to reorder before it runs out. The businesses that struggle are often not the ones with the least talent, but the ones still running on memory and guesswork.

Our ancestors by Lake Edward counted carefully with a bone and a stone. We have far better tools. The question is whether we use them.

What are you still running on guesswork that you could start counting this week?