PEOPLING

Kabwe: the Broken Hill Skull

~299,000 years ago

Palaeolithic · Middle Stone Age · MIS 8

A skull found in a Zambian mine in 1921 turns out to be about 299,000 years old: another human species lived in Africa alongside the first Homo sapiens.

The Broken Hill cranium, catalogued as Kabwe 1, ranks among the best preserved fossil human skulls. Miners working a metal ore body at Broken Hill, in what is now Zambia, took it from cave deposits in 1921. It served as the type specimen of Homo rhodesiensis and has more often been assigned since to Homo heidelbergensis. Its age long rested on comparison with faunas from other sites, which put it near 500,000 years. The cave was quarried away entirely, so no layer survives to date around the fossil, and the 2020 study therefore measured the specimen itself, by uranium-series analysis and by electron spin resonance, which reads the radiation dose stored in dental enamel since burial. The estimate returned is 299,000 years, give or take 25,000.

Why it matters

Shifting the skull from about 500,000 to about 300,000 years sets it beside the earliest fossils attributed to Homo sapiens instead of well before them. Late Middle Pleistocene Africa therefore held several human lineages at once, as Eurasia did: this population, Homo naledi further south, and the early sapiens forms. The stone tools recovered at the site belong to a transitional industry between the Early and the Middle Stone Age, which complicates the assumption that the Middle Stone Age was the work of the sapiens lineage alone.

Dating & uncertainty

The estimate is 299,000 years with an uncertainty of 25,000 at two standard deviations, hence a bracket from 324,000 to 274,000. It displaces a figure near 500,000 years drawn from faunal comparison, and no layer remains to arbitrate between the two: the mine consumed the cave, and everything now rests on measurements made on the fossil itself. Were the older figure restored, the skull would stand two hundred thousand years before the first Homo sapiens rather than alongside them, and the case for several contemporaneous African lineages would have to rest on other fossils.

Our species’ history as one day

01:13:0822 h 47 min before midnight

if the 315,000 years of Homo sapiens were compressed into a single day