The skull of a key African hominin, recovered from undated cave deposits in Zambia in the 1920s, now has a best age estimate of 299,000 years, reports a paper published this week in Nature. This helps to resolve the place of the Broken Hill (Kabwe) skull—which was originally described in Nature almost 100 years ago—in the hominin family tree.
The Broken Hill cranium was recovered from cave deposits in 1921 during metal ore mining. It was originally designated as a new species, Homo rhodesiensis, but recently it has been assigned to Homo heidelbergensis, a Middle Pleistocene species from Europe and Africa. Dating the find has been a challenge because the sediments in which it was found no longer exist. High concentrations of heavy metals in the sample have made radiometric dating of the specimen especially difficult. Therefore, the age of the cranium has been contentious; some researchers have placed it as old as 500,000 years.
Rainer Grun, Chris Stringer and colleagues analysed other fossil human remains (including a tibia and femur fragment) recovered from the same area the day after the cranium was discovered, as well as material scraped directly off the skull by researchers in the 1920s that was recently found in the archives of the Natural History Museum, London. The authors conclude that the skull is about 299,000 years old.
The findings suggest that—similar to Europe and Asia—Africa in the Middle Pleistocene epoch may have contained multiple contemporaneous hominin lineages, and that the Homo heidelbergensis/rhodesiensis complex may not represent a plausible last common ancestor for our own species.