Fostering the emergence of a knowledge society

In 1950, the Belgian geologist Jean de Heinzelin de Braucourt uncovered, at the site of Ishango, on the shore of Lake Edward near the Semliki, on what is now the border between the Democratic Republic of the Congo and Uganda, a fragment of long bone bearing engraved notches.

The object is dated to roughly twenty thousand years ago. It bears one hundred and sixty-eight notches, arranged in three distinct columns, and ends in an embedded shard of quartz.

One column has drawn more attention than the others: its groups set out 11, 13, 17 and 19 — every prime number between 10 and 20, and those alone.

Four readings, no consensus

• Deliberate arithmetic. This is Jean de Heinzelin's own reading: the groupings would reflect an operation of doubling and an empirical knowledge of number.
• A lunar calendar. Alexander Marshack proposed seeing in it a record of several lunar months — a hypothesis that accounts for the total without assuming any theory of numbers.
• A base-12 system. Vladimir Pletser and Dirk Huylebrouck have argued that the columns are organised around twelve and its divisors.
• A simple tally stick. The most economical explanation, and the one no available evidence allows us to rule out.

The caution

Olivier Keller warns against the central risk in this file: projecting our modern perception of number onto a Palaeolithic artefact. To read prime numbers in a series of notches already assumes that the engraver had the notion of a prime number — which is precisely what would need to be established.

We set out this controversy rather than pass over it. An object whose reading is forced ceases to be a source and becomes an illustration, and an institution that founds its name on an illustration forfeits the right to demand rigour of others.

Where the bone is kept

The bones are held at the Royal Belgian Institute of Natural Sciences, in Brussels. In November 2021, the Congolese Institute for Nature Conservation began proceedings for their return.

The question goes beyond the fate of an object. Scientific heritage kept outside its country of origin remains available for study, but it ceases to be transmissible — not to students, not to the public, not to researchers who cannot afford to travel.