Kabwe Skull: The Broken Hill Fossil from Zambia's Lead Mine

The Kabwe skull, also known as the Broken Hill skull, is one of the best-preserved early human fossils ever found. It was discovered by miners at the Broken Hill lead and zinc mine in what is now Kabwe, Zambia, in 1921, and was named Homo rhodesiensis that same year. In 2020 scientists dated it to about 299,000 years ago, revealing that its owner lived at the same time as some of the earliest Homo sapiens.

Discovery in a lead mine

Broken Hill, in the British colony of Northern Rhodesia, was a large lead and zinc mine where workers were quarrying into a hill riddled with caves filled with bones and mineral deposits. On 17 June 1921 the Swiss miner Tom Zwiglaar found a human skull deep in one of these cave passages, reportedly about 18 metres below the surface.

The skull was almost complete apart from part of the right side and the lower jaw. Other human bones came from the mine around the same time, including a tibia, parts of a pelvis and an upper jaw from a second individual, but because they were collected by miners rather than excavators, it is uncertain whether all of them belong together. The cave itself was later completely destroyed by mining.

Naming Homo rhodesiensis

The skull was sent to the British Museum (Natural History) in London, now the Natural History Museum. Later in 1921 the palaeontologist Arthur Smith Woodward described it in the journal Nature and named a new species, Homo rhodesiensis, popularly called “Rhodesian Man”.

It made an immediate impression. Its brow ridges are among the largest of any known human fossil, and its face is broad and long. Yet its brain size, estimated at around 1,230 to 1,300 cubic centimetres, is close to that of modern people. At the time, few human fossils were known from Africa, and Kabwe was the first important one, three years before the Taung Child was found in South Africa.

Bad teeth and other clues

The Kabwe individual, probably an adult male, had very poor dental health. Ten of the upper teeth have cavities, some of them severe, and there are signs of abscesses. It is among the earliest known examples of extensive tooth decay in a human. A partly healed lesion near the left ear has been interpreted as a possible sign of a chronic infection or a tumour, and some researchers think infection may have contributed to the individual’s death.

Dating the skull

For nearly a century the age of the skull was uncertain because its original context had been lost. Estimates based on animal fossils and the style of the skull ranged widely, from about 125,000 years to more than 500,000 years.

In 2020 a team led by the geochronologist Rainer Grün, including Chris Stringer of the Natural History Museum, analysed tiny samples from the skull itself and from associated material. Using uranium-series dating of the bone and teeth and electron spin resonance dating of the enamel, they obtained an age of about 299,000 years, with an uncertainty of around 25,000 years. Analyses of the lead and zinc content of the bones also helped to confirm which remains came from the same deposits.

A crowded human landscape

The new date placed Kabwe in a period when Africa was home to several very different kinds of humans. At roughly the same time, early Homo sapiens with modern-looking faces lived at Jebel Irhoud in Morocco, and the small-brained Homo naledi was present in South Africa.

This suggests that Homo sapiens did not evolve by a smooth, gradual transformation of one population, but emerged in a continent where diverse lineages coexisted. The Kabwe individual was probably not a direct ancestor of modern humans living at that date, though its population may have descended from groups related to our ancestors.

Researchers still debate how to classify it. Many group Kabwe with Homo heidelbergensis, a species named from a European jaw, while others prefer Homo rhodesiensis for African fossils of this kind. In 2021 some scholars proposed the name Homo bodoensis for this group, but the proposal has not been widely adopted.

Repatriation

Because the skull was removed to London during the colonial period, its ownership has become a political as well as a scientific question. The government of Zambia has repeatedly asked for its return, and the issue has been discussed between Zambian authorities and the Natural History Museum. Casts of the skull are on display in Zambia.

Timeline

• c. 299,000 years ago: The Kabwe individual lives in south-central Africa.
• 1921, 17 June: Miners find the skull at the Broken Hill mine.
• 1921: Arthur Smith Woodward names Homo rhodesiensis in Nature.
• 1924: The Taung Child is found in South Africa, adding to African fossil finds.
• 1964: Northern Rhodesia becomes independent as Zambia; Broken Hill is later renamed Kabwe.
• 2020, April: A study in Nature dates the skull to about 299,000 years ago.

Why it matters

The Kabwe skull is one of the most complete early human fossils known and a vital piece of evidence for human evolution in Africa. Its date shows that around 300,000 years ago several human lineages lived side by side, making the origin of our species a story of diversity rather than a straight line.