Kabwe 1, also known as Broken Hill Man or Rhodesian Man, is a nearly complete archaic human skull discovered in 1921 at the Kabwe mine, Zambia (at the time, Broken Hill mine, Northern Rhodesia). It dates to around 300,000 years ago, possibly contemporaneous with modern humans and Homo naledi. It was the first archaic human fossil discovered in Africa. Kabwe 1 was found near an exceptionally well-preserved tibia, as well as a femoral fragment and potentially other bones whose provenance is uncertain. The fossils were sent to the British Museum, where English palaeontologist Sir Arthur Smith Woodward described them as a new species: Homo rhodesiensis. Kabwe 1 is now generally classified as H. heidelbergensis. Zambia is negotiating with the UK for repatriation of the fossil.
Kabwe 1 is characterised by a massive brow ridge (supraorbital torus), a low and long forehead, a prominence at the back of the skull, thickened bone, and a proportionally narrow lower face. The tibia may have belonged to an individual who was about and in life, making it one of the largest known archaic humans. Kabwe 1 presents severe tooth decay, possibly caused by overloading of the teeth, age, and lead poisoning, which may have become septic and ultimately lead to the death of the individual.
Kabwe 1 is associated with Middle Stone Age tools made of quartz, possibly of the Lupemban culture. Kabwe 1 may have inhabited a cavern and butchered mainly large hoofed mammals. The Kabwe site probably featured miombo woodlands and dambos, like in recent times.
Research history Discovery
In 1902, engineer T. D. Davey discovered a major lead-zinc deposit in Northern Rhodesia and named it Broken Hill, possibly in reference to the Australian lead-zinc Broken Hill ore deposit. He claimed the six kopjes (hills) in the area, and mining commenced in 1904 under the authority of the Broken Hill Mining Company. In 1906, when mining reached full-scale production, excavators dug into what is now known as the "Bone Cavern" in No. 1 Kopje, yielding animal bones and stone tools. On June 17, 1921, Swiss miner Tom Zwiglaar documented a human skull at the back of the cavern when his "black boy" struck it with a pickaxe. Miners mistook a mineralised calcitic deposit as mummified skin. More fossils were reported the next year, and Czech-American anthropologist Aleš Hrdlička discovered more in 1925.
Like other fossils discovered at the site, the managing director of the company — Ross Macartney — sent the human remains to the British Museum. The first account of the skull's discovery was published in 1921 by the assistant electrometallurgist W. E. Harris in The Illustrated London News. That same year, English palaeontologist Sir Arthur Smith Woodward made a short preliminary report, and the skeleton was described by English osteologist William Plane Pycraft in 1928.
This was the first archaic human ever discovered in Africa, and at this point in time, many scientists had not expected to find such a specimen in this part of the world. The discovery elicited much scientific attention.
Provenance
Before mining operations, No. 1 Kopje was high with a depression in the middle. The Bone Cavern was at ground level, and the water table was about below. Mining activity has since destroyed the site. When it was open, the cavern may have been east to west and inhabited intermittently by humans and hyenas.
The skull was found in a mass of lead and was, at first, reported to have been found together with all the other human remains from the site. In 1928, British palaeontologist Francis Arthur Bather suggested that the entire skeleton had actually been found, but most of it was destroyed before its significance was understood. In 1929, Kenyan fossil hunter Louis Leakey interviewed miners working at the time and concluded that the skull was found in isolation, and workers subsequently searched the dumps for more fossils; because only lead-mining was happening at Broken Hill at the time, the other fossils must have originated from younger zinc deposits higher up. Therefore, it was possible the skull and the other fossils belonged to two different species. Similarly, when Hrdlička investigated the matter in 1930, Zwiglaar told him he found a human leg bone about from the skull, but no other human remains.
In 1947, to test the provenance of the fossils, the UK Government Chemist J. A. C. McClelland spectrographically measured the fossils' levels of lead, zinc, and vanadium. He found that the skull was the only fossil that contained more zinc than lead, and mentioned an unpublished record in the archives of the British Museum which reported that the skull was originally encrusted in hemimorphite (a zinc silicate). The skull may have occupied a zinc pocket within a lead carbonate mass. Because all other fossils have high amounts of lead, they probably similarly originate from the older lead deposits. It remains unclear if the unprovenanced fossils can be associated with the same species represented by Kabwe 1.
The provenanced fossil specimens are: E.686 (the skull) E.691 (left tibia) E.M.793 (femoral shaft)
The other unprovenanced fossils are: E.897 (skull fragment) E.687 (right maxilla) E.898 (distal right humerus) E.719 (right hip bone) E.720 (right hip bone) E.688 (sacrum) E.907 (proximal right femur) E.689 (proximal left femur) E.6891 (distal left femur) E.690 (left femoral diaphysis)
Hrdlička described the unprovenanced fossils as anatomically identical to modern humans. He was hesitant to assign them to the same species as Kabwe 1. In 1986, British physical anthropologist Chris Stringer noted at least one archaic feature on E.719, indicating that at least some of the unprovenanced fossils may represent an archaic human.
Age
Because of the uncertain provenance and the destruction of the site due to mining activity, determining a precise age for the Kabwe fossils has been problematic. They at first were assumed to date to the Late Pleistocene because they were found with animals still alive today, and were associated with early Middle Stone Age tools. In 1973, American palaeontologist Richard Klein redated the Middle Stone Age (and therefore the Kabwe material) to the late Middle Pleistocene. Biostratigraphic studies in the early 2000s drew comparisons with Olduvai Gorge and Elandsfontein, and similarly suggested a Middle Pleistocene age — maybe 500,000 years old. Kabwe 1 is also anatomically comparable to other African fossils better constrained to the early to mid Middle Pleistocene.
Using electron spin resonance dating (ESR) of dentin adhering to tooth enamel fragments, and laser ablation-inductively coupled plasma mass spectrometry of the inner and outer surfaces of a fragment of the base of the occipital bone of Kabwe 1, a 2020 study calculated an age of 298,000 ± 34,000 years for the former, and 301,000 ± 37,000 years for the latter method. They offered a best estimate of 299,000 ± 25,000 years (the weighted mean). Congruently, using uranium–thorium dating and ESR dating of the sediment scraped off the skull in 1921, they calculated an upper age limit of 322,000 years. The interval opens the possibility that Kabwe 1 was a contemporary of the Moroccan Jebel Irhoud 1, the oldest identified modern human fossil, and the South African Homo naledi.
Classification
When first detailing the Kabwe fossils in 1921, Woodward compared the skull to those assigned to Neanderthals (Homo neanderthalensis), namely La Chapelle-aux-Saints 1. He noted that while the face is similar (though "more simian in appearance"), the braincase aligns somewhat more closely with modern humans (H. sapiens), so he decided to name a new species: H. rhodesiensis. Woodward said this might revitalise the hypothesis that human evolution went through a Neanderthal phase, with H. rhodesiensis being the step after the Neanderthal. In other similar models, Kabwe 1 was believed to be the direct ancestor of modern South African bushmen, or "Australo-Melanesians" as a descendant of the Indonesian Solo Man. H. rhodesiensis was the third fossil member of the genus Homo, after H. neanderthalensis (Neanderthal 1) named in 1864, and H. heidelbergensis (Mauer 1) named in 1907.
In his 1928 description of the fossil material, Pycraft believed that the skull was more closely allied with chimpanzees and gorillas than Neanderthals, and the hip joint only permitted an apelike gait. He recommended placing the Kabwe fossils into a new genus as "Cyphanthropus rhodesiensis". Pycraft's description, comparisons, and inferences were criticised by British writer Frederick Gymer Parsons, who rejected "Cyphanthropus" later that year.
By the mid-20th century, human taxonomy was in turmoil, with several species and genera described on the basis of single specimens. In 1950, German-American evolutionary biologist Ernst Mayr, surveying a "bewildering diversity of names", subsumed human fossils into three species of Homo: "H. transvaalensis" (the australopithecines), H. erectus, and H. sapiens, as had been broadly recommended by various priors. Mayr defined these species as a sequential lineage, with each species evolving into the next (chronospecies). For Kabwe, he recommended that the specimen could, at most, be distinguished at subspecies level, as H. sapiens rhodesiensis. Though Mayr's recommendations became popular, this left H. erectus and H. sapiens poorly defined.
Kabwe 1 was widely classified under the umbrella of "archaic H. sapiens" (or H. sapiens sensu lato), a population which would eventually lead to anatomically modern H. sapiens (sensu stricto). Other Middle Pleistocene fossils were generally classified as either H. erectus or "archaic H. sapiens". In 1974, British physical anthropologist Chris Stringer noted that the Greek Petralona 1 was anatomically more comparable to Kabwe 1, Mauer 1, and the Hungarian Vértesszőlős than to East Asian Middle Pleistocene H. erectus. He proposed reviving the nomen heidelbergensis, classifying them as H. s. heidelbergensis — a widespread Euro-African subspecies, and the last common ancestor of modern humans (H. sapiens sapiens) and Neanderthals (H. sapiens neanderthalensis). At the time, he was hesitant to revive entire species for fear of recluttering human taxonomy, but in 1983, he proposed classifying them as a unique species as either H. heidelbergensis or H. rhodesiensis, depending on the inclusion of Mauer 1, as the common ancestor of H. sapiens and H. neanderthalensis. Since then, Kabwe 1, Petralona 1, the Ethiopian Bodo cranium, and the French Arago 21 have normally been discussed altogether as representatives of H. heidelbergensis.
Though H. heidelbergensis became a popular designation (and sometimes extended to East Asian Middle Pleistocene specimens), in 2000, American anthropologists Sally McBrearty and Alison S. Brooks argued that H. heidelbergensis should be reserved for only the direct ancestors of Neanderthals. They recommended reviving H. rhodesiensis to house African Middle Pleistocene fossils they believed were directly ancestral to modern humans. As the age of human fossils became better resolved, it was discovered that modern humans existed at the same time as Kabwe 1 and other divergent specimens.
The classification of Middle Pleistocene humans is a contentious matter, popularly termed "the muddle in the middle", but H. rhodesiensis is usually considered to be a junior synonym of H. heidelbergensis. In 2022, Serbian-Canadian palaeoanthropologist Mirjana Roksandic instead suggested expanding the definition of H. neanderthalensis to include Middle Pleistocene European specimens with Neanderthal traits, and housing African and non-Neanderthal European specimens in H. bodoensis instead of H. rhodesiensis to avoid honouring Cecil Rhodes. Her recommendations have been criticised for oversimplifying the archaeological record, and for violating the principle of priority.