Math & science · c. 22,000 years ago

Tally marks

Notches cut into bone keep a running count, the first external memory for numbers.

The Ishango bone from the Congo basin carries grouped notches roughly 20,000 years old, and the older Lebombo bone has 29. Tallies let people track days, animals and debts beyond what memory could hold, the seed of all later numerals.

See it in the living tree Wikipedia

Arcs above join it to what it stood on, arcs below to what it led to. The bar places this stretch on the tree's whole timeline.

What it built on 1

Spoken language 150k BCE

What it led to 1

Numerals and arithmetic 3000 BCE

Related measurements

The dashed line marks when it first worked.

World population over a million years Latest: 6.27k million people (2000) Source: DeLong 1998, table 'Total World Population' (Kremer series); Kremer 1993, Population Growth and Technological Change: One Million B.C. to 1990, QJE 108(3)

World GDP over a million years Latest: 41k billion 1990 international $ (2000) Source: DeLong 1998, Estimating World GDP, One Million B.C. - Present; Wikipedia: Gross world product (DeLong table, cross-check)