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'Last Common Ancestor' found in the Middle East?

The origins of anatomically modern Homo Sapiens have always been a mystery, especially as fossils discovered in the past are dated further and further back. 

The current consensus is that our species emerged around 250,000 years ago, coexisting with slightly more 'archaic' human groups such as Homo Rhodesiensis in southern Africa and Homo Sapiens Idaltu in Ethiopia. However, the origins of our evolutionary common ancestor with the Neanderthals, dubbed the Last Common Ancestor or LCA (not to be confused with the last common ancestor of chimps and hominids), are starting to be revealed, an ancestral species that would not look out of place today as toddlers. 

Recent research and new finds have set this origin between 1.2 million and 800,000 years ago, with a subsequent branching of the 'Neandersovans' into western and eastern halves, the Neanderthals and the Denisovans, dated genetically to 744,000 years ago. 

Now, in a open access paper released this week, two palaeoanthropologists have concluded that our LCA emerged, and diverged, in southwest Asia, and more specifically the Levant. This is consistent with earlier studies that found that the LCA could have emerged outside of Africa, following an 'Out-of-Africa' event by different hominids in the Early Pleistocene. The fossils and the archaeology in Africa itself assigned to early proto-Sapiens and Neanderthal ancestors all date well after this, from 400ka onward. However, it contradicts the prevailing theory that Homo Antecessor, a hominid with a flat, human-like face, and a mosaic of more Neanderthal and human-like features, represents our Last Common Ancestor. The authors consider that Antecessor, a species that lived roughly 1.2mya to 650ka in western Europe, might be a western offshoot of the original LCA that diverged early on. 


A possibly ~500ka skull from Zuttiyeh, Israel, the 'Cave of the Robbers'. Possibly a descendant or a close cousin of our LCA.

Why is any of this significant? Well, it provides a place to search for the earliest signs of our lineage - the first inklings of the kind of cognitive behaviour that would allow us to dominate other hominids and take over the natural world. If any DNA, trace proteins or tools are found, scientists could potentially assess how far more 'archaic' hominids, i.e. Homo Erectus and its many forms, influenced the development of human culture and behaviour. The Near Eastern location of the LCA could also help to explain the many geographically varied and hard to describe 'archaic' fossils distinct from Neanderthals, such as the Petralona skull (~260ka), the Homo Nesher-Ramla in Israel (~130ka) and Homo Bodoensis in Ethiopia, as separate offshoots from the LCA wellspring in the Fertile Crescent. The one hominid skull in India, the Narmada cranium (~300ka), might be another case of this. 

The chronological range of the original LCA - let's call it Homo Primigenius, or Progenitor Man - must have been quite short, probably a hundred thousand years before Antecessor diverged and some groups moved back into Africa. Their tool tradition may have been close to what Erectus had been making - early handaxes - and to what Antecessor made in Britain, which has been classified as a proto-Acheulean handaxe and pebble industry by several archaeologists. The only problem is that no physical evidence dating before 300,000 years ago in the region has survived, apart from Erectus fossils and tools at ‘Ubeidiya, dating back to 1.9mya. 


The proposed dispersal routes of our LCA; diverging east into Neandersovans and other subspecies, diverging west into Antecessor, and south to eventually evolve into Homo Sapiens. After Bermúdez de Castro and Martinón-Torres (2022)

The entire population of the LCA probably numbered no more than fifty thousand, considering estimates of hominid group size; a previous study found that the Neandersovans, who branched off from the LCA, interbred with an archaic species in Europe that numbered up to 200,000. That is all the more incredible considering how vast and varied these regions are; no doubt both groups were looking for each other, or else were after the same resources and territory. 

Although the study suggests a Levantine homeland on the basis of early Levantine fossils, there is nothing that rules out an Arabian, southern Anatolian or Persian Gulf homeland either. Arabia was easily accessible from coastal Ethiopia and Somalia, and it might not be a coincidence that the earliest fossils belonging to the Sapiens lineage are found there.

The brain size of Primigenius might not have been hugely smaller than ours, as Antecessor had a rough brain size of 1,000 cc, compared to the human average of 1,300 cc. Diet, climate, lifestyle, social complexity and interbreeding with smaller-brained hominids would have made this an ever-changing variable. Nevertheless, if the LCA had the same sized brain as a Neanderthal, a Denisovan and as other Sapiens ancestors, it may have had the ability to do and create the same things as they did. Maybe the first artists, the first ceremonies and the first spiritual beliefs, the first myths, started with them, out by the Pleistocene banks of the Euphrates, or by a hippo carcass on the shore of the Dead Sea.

References:

J.M. Bermúdez de Castro, M. Martinón-Torres (2022) The origin of the Homo sapiens lineage: When and where? Quaternary International. 

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