Dating the Broken Hill Skull – H. heidelbergensis Younger than Previously Thought

Palaeoanthropologists have long recognised that the evolution of the hominins and our own species (Homo sapiens), was complicated and not simply a linear transgression from one species to another.  Human fossil remains are exceptionally rare and sometimes, a new study can upend previously assumed concepts and ideas.  For example, a team of scientists including researchers from the Natural History Museum (London), Australian National University (Canberra), University College Dublin, Muséum national d’Histoire naturelle (Paris), University of the Free State (South Africa), University of Wollongong (Queensland), University of Southampton and Griffith University (Queensland), have published new dating information for a hominin skull discovered in 1921.

The skull representing Homo heidelbergensis turns out to be much younger than previously thought.

The Famous Broken Hill Skull (Kabwe 1) Homo heidelbergensis

Picture credit: The Trustees of the Natural History Museum

Studying Homo heidelbergensis

Writing in the academic journal “Nature”, the researchers conclude that this skull, previously thought to be around half a million years old, was much younger with an estimated date of between 274,000 and 324,000 years of age.  This result suggests that in the later stages of the Middle Pleistocene of Africa (Chibanian stage), there were many different types of hominin living at the same time.  Homo sapiens, H. heidelbergensis/H. rhodesiensis and Homo naledi were all contemporaneous.

The Broken Hill Skull

The skull studied, referred to as the Broken Hill specimen, currently resides in the collection of the Natural History Museum (London) and is on display in the Human Evolution gallery, but there are ongoing discussions about the return of this fossil to Africa.

The skull was discovered in 1921 by an African miner and his Swiss co-worker Tom Zwigelaar at the lead and zinc mine located at Broken Hill, which at the time was in northern Rhodesia but is now Kabwe in Zambia, hence the reference to the fossil skull as Kabwe 1.  Other fragmentary human remains were also found at the mine (partial upper jaw, tibia, sacrum and two elements from a femur from another individual).  The fossils were donated by the mining company to the then British Museum (Natural History Museum), at the time of their discovery anthropologists regarded these fossils as the most significant hominin fossils found on the African continent.

Early Photographs of Kabwe 1 (Broken Hill Skull)

Picture credit: Griffith University (Queensland)

Problems Dating the Skull and Fossil Bones

Nearly a hundred years ago, data recording surrounding such an important fossil discovery was nowhere near as thorough at it is today.  Mining work continued in the area where the skull and other bones had been found so any evidence to help accurately date the fossils was subsequently lost.  Assigned to Homo heidelbergensis, the skull was originally dated to around 500,000 years ago.  However, these researchers, led by Professor Rainer Grün (Environmental Futures Research Institute at Griffith University), subjected the skull and the other hominin fragments from the site to radiometric dating and determined that these people lived between 274,000 and 324,000 years ago.

Commenting on the importance of this research, Professor Grün stated:

“The new best age estimate of the fossil impacts our understanding of the tempo and mode of modern human origins”.

One of the co-authors of the scientific paper, Professor Chris Stringer (Natural History Museum), added:

“Previously, the Broken Hill skull was viewed as part of a gradual and widespread evolutionary sequence in Africa from archaic humans to modern humans.  But now it looks like the primitive species Homo naledi survived in southern Africa, H. heidelbergensis was in Central Africa, and early forms of our species existed in regions like Morocco and Ethiopia.”

Homo rhodesiensis and Piltdown Man

It was Sir Arthur Smith Woodward, the curator of the Geology Department at the British Museum who proposed the new species Homo rhodesiensis to describe the Kabwe 1 skull as “Rhodesian Man”.  However, most scientists now consider H. rhodesiensis to be junior synonym of H. heidelbergensis or possibly an African sub-species of it.  Despite a prestigious academic career, Sir Arthur is best remembered for his association with the Piltdown Man hoax of 1912.  Even on his deathbed, he still believed that the fossil remains found in a Sussex gravel bed at Barkham Manor, near to Piltdown Common, represented a species of archaic human, unlike any other species of early hominin known to science.

Unfortunately, for Sir Arthur, five years after he died, new dating techniques proved the human skull bones from the site to be less than 500 years old.

The new, younger date for the Kabwe 1 skull also casts a cloud over the provenance of stone tools associated with hominin fossils from the late Middle Pleistocene.  As scientists have evidence to indicate Homo heidelbergensis present in Africa as recently as 300,000 years ago, stone tools from this date may not have been crafted by our species.

Not All the African Stone Tools Around 300,000 Years of Age Can be Ascribed to our own Species

Picture credit: Dr Nicholas Conrad/University of Tubingen

The new age estimate for Kabwe 1 raises questions about our own evolution.  It casts doubts on the presumption that H. heidelbergensis/H. rhodesiensis was a direct ancestor of our species Homo sapiens.  This research suggests that there were multiple contemporaneous hominin lineages in Africa during the later stages of the Middle Pleistocene, reflecting a similar model found in Eurasia.

• African hominins (late Middle Pleistocene) – H. sapiens, H. naledi, H. heidelbergensis/H. rhodesiensis
• European/Asia hominins (late Middle Pleistocene) – H. neanderthalensis, H. luzonensis, H. floresiensis, the Denisovans and perhaps also H. heidelbergensis and H. erectus

Everything Dinosaur acknowledges the assistance of a media release from Griffith University in the compilation of this article.

The scientific paper: “Dating the skull from Broken Hill, Zambia, and its position in human evolution” by Rainer Grün, Alistair Pike, Frank McDermott, Stephen Eggins, Graham Mortimer, Maxime Aubert, Lesley Kinsley, Renaud Joannes-Boyau, Michael Rumsey, Christiane Denys, James Brink, Tara Clark and Chris Stringer published in Nature.

To read an article about the presence of H. heidelbergensis in Kent: Giant Prehistoric Straight-tusked Elephant Butchered by H. heidelbergensis.

The Everything Dinosaur website: Everything Dinosaur.