Ancient human species settled African highlands 2 million years ago 

A reanalysis of an ancient fossil has shed new light on the adaptive behaviour of ancient humans in Africa. 

The fossil – of an infant jawbone – was uncovered in 1981 at the Melka Kunture archaeological site in the Ethiopian Highlands southwest of Addis Ababa. But it has since been subject to extensive debate as to its “taxonomic affinity”.  

Basically, archaeologists weren’t sure which hominid species the jaw belonged to, with at least four early human species considered possible. 

Scans of a 2 million year old jawbone
Images of the fossil mandible from the Garba IV archaeological site near Melka Kunture. Credit: Mussi et al (2023).

That it was found in the presence of some of the earliest known stone tools, usually described as belonging to the Oldowan and subsequent Acheulean “industries” of prehistoric toolmaking, also presented a problem – which group had been practising these earliest forms of toolmaking? 

Now, an extensive cross-institutional study published today in the journal Science has reevaluated the fossil and proposed a new perspective on the movements of ancient humans in this part of Africa. 

Led by Professor Margherita Mussi, the director of the Italo-Spanish Archaeological Mission at Melka Kunture, the study team has now identified the mandible as one of the earliest fossils of Homo erectus – an early hominid that emerged from Africa, spread across Asia and which was recorded in Indonesia as recently as 100,000 years ago. 

Using synchrotron imaging, Mussi and her colleagues were able to closely study the enamel and surfaces of the infant’s teeth in comparison to other hominid specimens recorded from other parts of Africa. 

They were able to narrow the external and internal features of the jawbone to Homo erectus. Connecting these to the small pointed Oldowan and Acheulean tools means H. erectus can be directly associated to instruments from the Early Pleistocene.  

It also means Acheulean tools uncovered in strata above the mandible have been dated at around 1.95 million years.  

From this, Mussi’s team argue changes in climate may have forced ancient hominids to migrate to new locations, and that H. erectus may have been better adapted to survive in higher altitudes such as those where the infant jawbone was discovered. 

“The aridification of Africa, which started after 2.8 [million years ago], could have driven hominin groups beyond previously occupied environments,” they write. 

“A highland environment… At an altitude of 2000m [above sea level] and more, exposes individuals to less oxygen, higher exposure to UV rays, more rain and cooler temperatures. 

“The larger-bodied and larger-brained H. erectus was possibly better adapted to the highlands than smaller-bodied hominins.” 

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