The Origin of West Africans

According to the article “Recovering Signals of Ghost Archaic Introgression In African Populations” [Link], which was published in 2020, West Africans possess ancestry from an archaic human species that diverged from the lineage of Homo sapiens before Neanderthals did so. It reads as follows.

"We provide complementary lines of evidence for archaic introgression into four West African populations. Our analyses of site frequency spectra indicate that these populations derive 2 to 19% of their genetic ancestry from an archaic population that diverged before the split of Neanderthals and modern humans. We determined the posterior mean for the split time to be 625,000 years before the present."

However, the article “Reconstructing Prehistoric African Population Structure” [Link], which was published in 2017, says that West Africans possess ancestry from the very first Homo sapiens to split into their own lineage rather than ancestry from an archaic human species. It reads as follows.

"The possible basal western African population lineage would represent the earliest known divergence of a modern human lineage that contributed a major proportion of ancestry to present day humans. Such a lineage must have separated before the divergence of San ancestors, which is estimated to have begun on the order of 200 to 300 thousand years ago. Our genetic data do not support the theory that this putative basal lineage diverged prior to the ancestors of Neanderthals, since the African populations we analyze here are approximately symmetrically related to Neanderthals."

A third scientific article, titled “Ancient West African Foragers in the Context of African Population History” [Link], which was published in 2020, reconciles the conclusions of the first two articles. It states that West Africans possess DNA from both an ancient modern human lineage and an archaic human lineage. The following is a quote from the article.

"The West African clade is distinguished by admixture from a deep source that can be modelled as a combination of modern human and archaic ancestry. The modern human component diverges at almost the same point as Central and southern African hunter-gatherers, while the archaic component diverges close to the split between Neanderthals and modern humans."

Note that Central African hunter-gatherers are African Pygmies and that southern African hunter gatherers are Khoi and San peoples.

Note also that because Homo heidelbergensis was the most recent common ancestor of Homo sapiens and Neanderthals, that the archaic human species must have shared Homo heidelbergensis as its most recent common ancestor, due to diverging from the shared lineage of Homo sapiens and Neanderthals close to the time that Neanderthals did so.

Furthermore, note that the third article describes the admixture of West Africans as coming "from a deep source that can be modelled as a combination of modern human and archaic ancestry," which implies that West Africans inherited both forms of ancestry from a single population.

The third article clarifies the percentage of each type of ancestry that West Africans have inherited from this population. The following is another quote from the article.

"We estimate the shared admixture to introduce 10% deep modern human and 2% archaic ancestry, although the first proportion is not well constrained. An alternative model with no archaic component, in which the West African clade receives deep ancestry from a single source, also provides a reasonable fit to the data, although it does not account for previous evidence of archaic ancestry in sub-Saharan Africans.”

2% is a more reasonable amount of admixture relative to the aforementioned range of 2% to 19%. The reason is that if the admixing event occurred thousands of years ago, then the DNA from the archaic human species would have spread throughout the population evenly by the modern era, resulting in a narrow range of percentages or a single percentage value of archaic DNA per individual.

Excerpt From the 2nd Article

According to the 2nd article, the admixing event supposedly occurred 43,000 years ago. Therefore, there has been more than enough time for the DNA to spread evenly throughout the populations of West Africa and thus result in a consistent value per individual West African.

Excerpt From An Article Pertaining to An Admixture Event of Non-Africans

Consider that the modern human ancestors and the Neanderthal ancestors of non-Africans also engaged in an admixture event tens of thousands of years ago, or, to be specific, effectively 47,000 to 65,000 years ago.

Excerpt From An Article Explaining the Percentage of Archaic Ancestry In Certain Non-Africans

Due to how many generations ago that admixture event occurred, modern non-Africans are between only 1% and 4% Neanderthal. The narrowness of the range and the low value of the range's upper bound are in accord with the number of generations that there has been since that admixture event. So should be the admixture of West Africans, as is concluded by the third article.

In regard to the deep modern human component that comprises 10% of West Africans' ancestry, there are human fossils that have been discovered in Jebel Irhoud - Morocco, which is in North Africa. Their estimated age matches the estimated time period that the second article says was when the deep modern human lineage of West Africans diverged, which was 200,000 to 300,000 years ago. Correspondingly, the fossils of Jebel Irhoud - Morocco are estimated to be 254,000 to 318,000 years old.

Therefore, the two estimated ranges of time overlap. This indicates that the Jebel Irhoud fossils could be from a generation that lived relatively soon before or after the deep modern human ancestors of West Africans diverged from the non-deep modern human ancestors of West Africans and all other extant populations.

The fossils represent a stage of evolution that characterized modern humans from whom all extant populations descend. However, whereas most extant populations' modern human ancestors diverged from one another at a later stage of evolution, the deep modern human ancestors of West Africans would have diverged at or near these fossils' stage of evolution.

This is precisely why the deep modern human ancestors of West Africans are described as "deep." They diverged at a deep point in the past. However, they would have continued to evolve, but in different ways due to separating from all other contemporary modern humans of their time.

Note that the estimated age of the fossils corresponds to the estimated time at which Homo sapiens formed, and that the fossils' mixture of archaic and modern traits is what should be expected regarding the basal stages of Homo sapiens’ development.

The fossils represent the phase during which the shared modern human ancestors of everyone alive today were transitioning from archaic humans into modern humans, or, more specifically, from Homo heidelbergensis to Homo sapiens. Therefore, the population from which they came can be referred to as basal Homo sapiens or basal modern humans.

Correspondingly, there is a rare paternal haplogroup that has been estimated to also be 200,000 to 300,000 years old, which means that it formed during the time period from which the Jebel Irhoud fossils came - or relatively close to that time period. It has been designated A00 [A Zero Zero] due to being older than any other extant human paternal haplogroup that has been discovered. Additionally, subclades of it have been found in the DNA of certain West Africans, namely men of the Mbo and Bangwa tribes of Cameroon. Therefore, the human fossils of Jebel Irhoud - Morocco are a good means of determining the identity of West Africans' deep modern human lineage.

The fossils have large brow ridges and crania that are long and narrow, whereas extant modern humans have practically non-existent brow ridges and crania that are globular. However, the facial morphology of the fossils falls within the range of extant modern humans. Also, like extant modern humans, they lack the occipital bun of Neanderthals and Homo heidelbergensis; Homo heidelbergensis is ancestral to not only Homo sapiens, Neanderthals, and the archaic human ancestors of West Africans - but to also another species tentatively called Denisovans, which is suspected of being Homo longi. Furthermore, the Jebel Irhoud fossils' crania are taller than those of Homo heidelbergensis and Neanderthals, which is why they have relatively vertical foreheads, though their foreheads slope backwards to a greater degree than those of anatomically modern humans.

Their relatively vertical foreheads is due to the expansion of their skulls' frontal bone relative to their Homo heidelbergensis ancestors and their Neanderthal cousins. This indicates that the frontal lobes of their brains were larger than those of their Homo heidelbergensis ancestors and their Neanderthal cousins, and that therefore their cognition and social intelligence were greater; these are fundamental differences between Homo sapiens and archaic human species.

Note that there are no known fossils of the unknown archaic human species that comprises 2% of West Africans' DNA, and there are no verified fossils of Denisovans beyond teeth, a fragment of a finger, a partial mandible, and a fragment of an arm or leg. The Dragon Man fossil, which has been assigned the species name "Homo longi," is suspected of being the skull of a Denisovan, but it has yielded no DNA and therefore cannot be verified as being the skull of a Denisovan. Therefore, the unknown archaic human species and Denisovans cannot be compared to the Jebel Irhoud fossils.

The population of basal modern humans from which the Jebel Irhoud fossils came could have split into two populations, or it could already have been one of two populations that had split from each other:

• One that had already spread throughout North Africa, which includes the Sahara, or that spread throughout this region later. This population shall be called the North African basal modern humans. They could have eventually evolved into a subspecies of modern humans that was different from anatomically modern humans, who shall therefore be referred to as the North African divergent modern humans.

• As for the other population of basal modern humans, they could have traveled to East Africa, or they could have already been there if that is where the split between them and the population of North Africa occurred. Afterwards, they could have eventually evolved into anatomically modern humans. This scenario is possible and likely because it is in East Africa, specifically Ethiopia, where the oldest fossils that are recognized as anatomically modern humans were discovered.

Afterwards, the anatomically modern human ancestors of West Africans and the North African divergent modern humans could have encountered one another, when the former migrated from East Africa to North Africa.

Since the anatomically modern human ancestors of West Africans would have had to travel through North Africa to reach West Africa, they would have encountered the North African divergent modern humans, assuming that the latter were not restricted to Morocco. And, as shall be proven, they were indeed not restricted to Morocco but were spread throughout North Africa.

Note that this scenario implies that the North African divergent modern humans would have also been the source of the 2% archaic ancestry of West Africans. This, in turn, implies that the North African divergent modern humans would have interbred with the unknown archaic human species that is the ultimate source of the 2% archaic ancestry of West Africans.

The possibility that West Africans' anatomically modern human ancestors bred with the North African divergent modern humans is supported by evidence that West Africans descend from people who inhabited North Africa.

Recall that a subset of West Africans possess subclades of the rare paternal haplogroup A00 [A Zero Zero] and that it formed during the time period from which the Jebel Irhoud fossils came, or relatively close to that time period (200,000 to 300,000 years ago). Therefore, there is the possibility that West Africans inherited A00 [A Zero Zero] from the North African divergent modern humans, since they would have been the descendants of the North African basal modern human population from which the Jebel Irhoud fossils came. And since the Jebel Irhoud fossils were found in … Jebel Irhoud - Morocco, which is in North Africa, then the divergent modern human descendants of their population may have also inhabited North Africa.

Furthermore, according to the third article, "Ancient West African Foragers in the Context of African Population History," the remains of four Shum Laka Foragers, who lived 3000 to 8000 years ago in western Cameroon, were analyzed and one of them possessed A00 [A Zero Zero]. The portion of the Shum Laka Forager's ancestry from which he inherited A00 [A Zero Zero] was a West African source that may have come from north of Cameroon, which indicates North Africa. The article states the following.

"Our analyses show that the 4 sampled children from Shum Laka can be modelled as admixed with about 35% ancestry related to hunter-gatherers from western Central Africa and about 65% from a basal West African source. The second component may have its origins farther to the north, given the geography and phylogeny of the other populations we studied. Moreover, gene flow from the north before 8000 BP is plausible in light of a short period of Saharan aridification, which could have contributed to population movements."

Additional evidence is the conclusion of Bioarcheologist Joel D. Irish regarding human fossils from North Africa that are 8000 years old. In the document, "Tracing the “Bantoo Expansion” from its source: Dental nonmetric affinities among West African and neighboring populations," Joel D. Irish concludes that these fossils share dental affinities with modern West Africans and Bantu peoples.

As can be seen in the composite photo that is below, the 8000 year old skull from North Africa, which is on the left, is very similar to the modern skull from the Congo, which is on the right.

Note that even though the Congo isn't technically part of West Africa, but is instead part of West Central Africa, its peoples belong to the same macro group as West Africans; this macro group is referred to as the Niger-Congo group, and it includes West Africans and the Bantu peoples of Sub-Saharan Africa. West Africans and Bantu peoples are genetically similar and possess the same maternal and paternal haplogroups. To be specific, they all possess subclades of Paternal Haplogroup E-M96, mainly but not exclusively through E-V38 (E1b1a), and they all possess subclades of Maternal Haplogroups L1, L2, and L3.

Joel D. Irish's overall conclusion is that West Africans and Bantu peoples descend from peoples who inhabited the Sahara, which is in North Africa, prior to 8000 years ago. However, as the Sahara transformed from an environment of grass, trees, and lakes into a desert starting 8000 years ago, these pre-historic peoples migrated southwards for greener pastures.

Therefore, it is highly likely that West Africans have ancestry from the North African divergent modern humans. What likely occurred was a migration of anatomically modern humans from East Africa into the Sahara tens of thousands of years ago. These particular anatomically modern humans would have carried subclades of Paternal Haplogroups D0 [D-Zero] and E-M96 (mainly via E-V38 [E1b1a]) - and subclades of Maternal Haplogroups L1, L2, and L3.

While in the Sahara, they would have encountered the North African divergent modern humans, who would have carried archaic ancestry as a result of previously breeding with an unknown archaic human species. The North African divergent modern humans would have also carried subclades of Paternal Haplogroup A00 [A Zero Zero] and subclades of an unknown maternal haplogroup or multiple unknown maternal haplogroups.

As the deep modern human and archaic ancestry of West Africans comprise a minority of their DNA, the anatomically modern human ancestors of West Africans either outnumbered the North African divergent modern humans or did not breed with them extensively.

This raises the question, who were the North African divergent modern humans? In order to answer this question, we must first consider the date of the admixture event through which West Africans have inherited deep modern human and archaic ancestry. As already shown, the first aforementioned article says that it occurred effectively 43,000 years ago.

Jebel Irhoud - Morocco, where the aforementioned human fossils that are approximately 300,000 years old were found, is located in North Africa; and there was a particular people present in North Africa when the admixing event is estimated to have occurred: the Aterians. Archaeological evidence of these people indicates that they were present throughout North Africa from 150,000 to 20,000 years ago, within which fits the effective time at which the admixture event occurred (43,000 years ago).

Aterian human fossil Dar Es Sultane II H5 and a reconstruction of Dar Es Sultane II H5 by Ancestral Whispers [Link].

There are fossils of Aterian tools and other materials that were discovered in Morocco, too, as well as Tunisia, Libya, Niger, and Egypt. Note that Niger is the specific country in which were found the aforementioned 8000-year-old skulls that share affinities with West Africans and Bantu peoples.

Map Highlighting Archeological Sites of the Aterian Stone Tool Culture [Link]

Additionally, there are Aterian human fossils that are estimated to be 100,000 years old and that were discovered in Morocco.

One of the Aterian human fossils that were discovered in Morocco is designated Dar Es Sultane Two H5, and it's estimated to be 100,000 years old.

Note that Morocco, where this human fossil was found, is, as already stated, the country in which Jebel Irhoud is located, and therefore is the same country in which the 300,000-year-old fossils of basal modern humans were discovered.

It's an adult skull, and it essentially looks like one of the skulls found at Jebel Irhoud - but larger. Hence, given the morphological similarities and the shared geographical location of these two fossils, it's likely that the population from which Dar Es Sultane Two H5 came descended from the North African basal modern humans.

Dar-Es Sultane II H5 (left) and Jebel Irhoud 1 (right).

The following is a quote regarding Dar Es Sultane II H5 from the scientific article "The origin and Evolution of Homo sapiens," which was published in 2016.

"The Moroccan cave of Dar Es Sultane Two has produced an immature calvaria, an adolescent mandible and the anterior part of a skull with associated hemimandible. The anterior vault of Dar Es Sultane Two H5 is high and very large, with a strong but divided supraorbital torus over a low, broad and flat face, with a low but broad nose. There are indications of a canine fossa and of alveolar prognathism. The mandible and the preserved posterior dentition are also large, but illustrations are deceptive in indicating the lack of a chin. The symphysial region is in fact broken off.

Deciding on how to classify Dar Es Sultane Two H5 is difficult. It has a rather modern looking face and frontal bone shape, but both are very large in size, as is the supraorbital development. Although previous assessments have suggested that it could represent an Aterian intermediate between the Middle Stone Age associated Irhoud specimens and those of the Iberomaurusian, (i.e. the local late Upper Paleolithic) morphometric analyses place it closer to Jebel Irhoud 1 and the Qafzeh crania than to the late Pleistocene fossils."

Two of the traits of Dar Es Sultane Two H5 that are mentioned in the quote are common in West Africans: broad noses and alveolar prognathism.

West Africans could possibly have other traits from this population, but these other traits could affect their internal biology rather than their phenotype.

Considering that only 12% of West Africans’ DNA comes from a lineage that provided them with deep modern human and archaic ancestry (10% and 2%, respectively), which has been determined herein to have been the Aterians, then it’s logical that West Africans don’t have all of their traits. Instead, they have only those that have remained through natural selection and sexual selection, which are two aspects of biological evolution. In other words, the traits from the Aterians that they do not have were probably disadvantageous for survival or unattractive to mates. Subsequently, the individuals who had them gradually became less and less of their population with each generation until they disappeared.

The ideas presented herein are hypotheses and therefore may be supplanted if there arises evidence that indicates alternate possibilities. Please be sure to express your thoughts on these hypotheses, and thank you for reading.