A new paper published by Professor Úlfur Árnason, a neuroscientist at the University of Lund in Sweden, places the last common ancestor of Homo sapiens sapiens and Neanderthals somewhere in Eurasia. Árnason argues that the ancestors of the African KhoeSan and Mbuti populations formed the first exodus of Homo sapiens sapiens into Africa from Asia and Europe.
It is commonly held that the original members of the Homo sapiens species, lived somewhere in Africa and that Homo sapiens sapiens emerged first on the same continent. The majority of scientists believe that only the exact dating of the emergence of our sub-species remains to be resolved. Not so fast, says Professor Árnason, his research suggests that the origination of the Homo sapiens sapiens sub-species was a Eurasian affair.
Scientific research suggests that Neanderthals and modern humans parted ways, genetically, sometime earlier than 500,000 years ago. Árnason argues that this date, along with what is known of Neanderthal geographic range, places the first of our own sub-species somewhere in Eurasia.
“The exclusive occurrence of Neanderthals in Europa and Asia and their absence from Africa restricts their origin to Eurasia. As a consequence, the origin of their sister-group, Homo sapiens sapiens, should be placed in the same continent, i.e. Eurasia (the Askur/Embla hypothesis, Árnason, 2016), in compliance with the LCA (last common ancestor) understanding that the LCA(s) of any two sister groups cannot be separated, neither in time nor space.”
We can boil down the first part of the argument to the fact that Neanderthals are not known to have been in Africa suggesting emergence in Eurasia, if Neanderthals emerged in Eurasia then the ancestral group they diverged away from, archaic Homo Sapiens, should also have been living there. It is a logical argument and one with considerable merit. It is certainly true that Homo erectus, the best candidate for Homo sapiens immediate ancestor, had spread across much of the planet by as early as 1.8 million years ago.
There is increasing evidence that the early humans ancestral to both sub-species were already present in Eurasia before the split that gave rise to Neanderthals, Denisovans and Sapiens (Homo sapiens sapiens) and that humans almost identical to those of living populations had emerged in East Asia long before they appeared in the African fossil record. Fossils of seemingly modern humans have been announced by archaeologists working at several Chinese digs, with associated dates ranging from 80,000 to 178,000 years in age.
Professor Árnason points to data emerging from the 2016 study The Simons Genome Diversity Project, considered a landmark genetic survey, which suggests that by 200,000 years ago populations of modern humans were already diverging into new genetic groups. This incredible realisation supports a model in which Africans and non-Africans began to part ways, in terms of genetics, close to the date associated with the earliest accepted fossils of modern humans (the 195,000-year-old Omo fossils).
It is difficult to understand why two populations in the same region would simply stop mixing for tens of thousands of years, such clean breaks are normally only observed after migration events. Árnason also notes that the deepest divergence was only observed when contrasting the genomes of the Khoesan people and non-Africans.
“The study of Mallick et al. (2016) showed that the ancestral Hss population had begun to develop genetic substructures > 200,000 YBP, an age that is compatible with the commonly accepted estimates of the basal divergence of extant Hss. Furthermore, the analysis demonstrated that the basal divergence among extant Hss fell between non-Africans (as represented by a French genome) and Africans (as represented by KhoeSan and Mbuti).”
The Simons Genome Project presented evidence of an additional Homo sapiens sapiens divergences involving the Yoruba, a West African population usually posited to be the living descendants of the population responsible for founding all non-African lineages.
Two competing models can be extrapolated from the available data, as depicted in the phylogenies trees ‘a’ and ‘b’ shown above (Fig.2).
Tree ‘a’ depicts early Homo sapiens emerging in Africa with the three subspecies, Neanderthals, Denisovans and Sapiens subsequently arising on the continent sometime earlier than 500,000 years ago. Neanderthals and Denisovans migrated out from Africa immediately after they diverged from Sapiens leaving no fossil remains and no genetic signature.
Hundreds of thousands of years after other humans left Africa the ancestors of the Khoisan and Mbuti diverged away from the ancestors of the Yoruba, close to 200,000 years ago. These African populations then remained separate on the same continent until members of the population ancestral to the Yoruba migrated out of the continent and colonised the planet 70,000 years ago.
Model ‘b’ argues that the archaic ancestors of Homo sapiens had reached Eurasia before the divergence of Neanderthals, Denisovans and Sapiens. Neanderthals and Denisovans subsequently remained in Eurasia, never encountering Africans.
Around 200,000 years ago, a group of Homo sapiens sapiens broke away from the greater Eurasian population and migrated into Africa, becoming the ancestors of the KhoeSan and the Mbuti. Close to 70,000 years ago a second migration event carried the ancestors of the Yoruba into Africa.
“The support for an African divergence between Homo sapiens neanderthalensis (Hsn) and Homo sapiens sapiens (Hss) is hypothetical, however, considering the absence of any palaeontological or archaeological Hsn finds in Africa. The molecular problems related to OOAH are of a similar nature as these results have been interpreted just in accord with the preconception of a basal Hss divergence in Africa, a supposition that automatically followed the hypothetical placement of the Hsn/Hss divergence in that continent.”
The information in Table 1 strongly suggests that there was a significant early period reduction in interbreeding between non-Africans and KhoeSan compared to that between non-Africans and the ancestors of the Mbuti. The same pattern of divergence can be seen in the data for estimates of the Yoruba/KhoeSan and Yoruba/Mbuti interbreeding. When we place this information into the correct context it suggests that the ancestors of the KhoeSan and Mbuti parted ways long before the estimated age, 131,000 YBP, of the 50% coalescence mark. The disparity between the estimated dates for the KhoeSan and Mbuti may indicate two separate migration routes taken from Asia to Africa at somewhat different times.
“The estimates in Table 1 show consistency between the deepest estimates (estimated age of 75% coalescence) related to the divergence between non-Africans (French) and KhoeSan (173,000 YBP) and non-Africans and Mbuti (171,000 YBP). This agreement has become erased at the next mark (50% coalescence) as it shows instead a non-Africans/ KhoeSan estimate of 131,000 YBP and a non-Africans/Mbuti estimate of 112,000 YBP. “
To better illustrate the two favoured routes of the exodus into Africa the map (Fig 3) shows the KhoeSan taking a southern route via the Bab el Mandeb Straights and the Mbuti and Yoruba are taking the Sinai route. The KhoeSan and Mbuti may have taken the same or different routes into Africa, this is not known.
The fossils of early modern humans found in China easily fit with the Out of Eurasia and Into Africa hypothesis, explained by the existence of a continuous Homo sapiens sapiens presence in Asia with no requirement for a hypothetical population from Africa that later became extinct. This Out of Eurasia model also readily encompasses the evidence that Neanderthals and Sapiens interbred over 220,000 years ago in Europe, and 130,000 years ago in Siberia, currently problematic for Out of Africa Theory.