Fossil skull casts doubt over modern human ancestry

The new paper entitled ‘Dating the Broken Hill (Zambia) skull, and its position in human evolution’ published in Nature on 2 April 2020 led by Griffith University, casts doubt over modern human ancestry and the ancestry of Homo sapiens.

The Broken Hill (Kabwe 1) skull is one of the best-preserved fossils of the early human species Homo heidelbergensis and was estimated to be about 500,000 years old.

Professor Rainer Grün from the Environmental Futures Research Institute led the team which analysed the skull and other fossil human remains found in the vicinity including a tibia and femur midshaft fragment. The material is curated at the Natural History Museum in London, where collaborators Chris Stringer and Michael Rumsey work.

Discovered in 1921 by miners in Zambia, the Broken Hill remains have been difficult to date due to their haphazard recovery and the site being completely destroyed by quarrying.

Using radiometric dating methods, Professor Grün and Dr Joannes-Boyau performed the analyses on the remains directly using a unique method they have developed and improved for more than a decade. The new refined dating now places the skull at a relatively young date, estimating it is between 274,000 and 324,000 years old.

Publishing their findings and methodology in Nature, Professor Grün said “the new best age estimate of the fossil impacts our understanding of the tempo and mode of modern human origins.”

“The Broken Hill human fossils are now within the time range of the early Middle Stone Age (MSA), challenging assumptions that only Homo sapiens were the craftsmen of MSA stone tools in Africa,” Professor Grün said.

Southern Cross University’s Dr Renaud Joannes-Boyau said the research also suggests that human evolution in Africa around 300,000 years ago was a much more complex process, with the co-existence of different human lineages.

“Approximately 300,000 years ago, earth and in particular Africa was populated with several species of humans that since have all disappeared except for our species Homo sapiens,” Dr Joannes-Boyau said.

“This paper is another example of the complexity behind human evolution and the mechanisms that led us to be the lone species”.

Professor Stringer said “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 primitive species such as 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”.

The team’s research adds to new and emerging studies which question the mode of modern human evolution in Africa and whether Homo heidelbergensis is a direct ancestor of our species.