Ghost DNA Found In West Africans Came From Mysterious Species Of Ancient Humans

Ancient humans in what is now West Africa appear to have procreated with another group of ancient humans that scientists were unaware existed. This event likely took place around 50,000 years ago. Homo sapiens once coexisted with other groups that diverged from the same genetic family tree at various points throughout history. Additionally, there is evidence originating from various regions of the world indicating that early humans inbred with other hominins, such as Neanderthals.

Researchers asserted that the evidence can be found in the DNA of present inhabitants of West Africa, despite the absence of any bones or ancient DNA to support their claims. Scientists examined the genetic material of hundreds of people from Nigeria and Sierra Leone and found evidence of what they call “ghost” DNA, which comes from an ancestor that is unknown to them.

In a 2020 study published in the journal Science Advances, geneticists Arun Durvasula and Sriram Sankararaman of the University of California, Los Angeles referred to this enigma as the “ghost archaic population.” Their discovery may shed light on the human genetic diversity in Africa, which has been difficult to chart up until now due to the limited fossil record. “We don’t have a clear identity for this archaic group,” Sankararaman said. “That’s why we use the term ‘ghost.’ It doesn’t seem to be particularly closely related to the groups from which we have genome sequences from.” (Source)

This study expands on previous research that has been conducted over the past ten years about ancient DNA retrieved from human fossils. In 2010, a group of scientists announced the publication of the first genome of a Neanderthal. They later discovered DNA from fossils in a cave in Siberia that was called Denisova. This genetic material belonged to a second linegae of humans known as Denisovans, who turned out to be closely linked to Neanderthals.

ghost dna
Four different Australopithecus crania that were found in the Sterkfontein caves, South Africa. The Sterkfontein cave fill containing this and other Australopithecus fossils was dated to 3.4 to 3.6 million years ago, far older than previously thought. The new date overturns the long-held concept that South African Australopithecus is a younger offshoot of East African A ustralopithecus afarensis. (Image credit: Jason Heaton and Ronald Clarke, in cooperation with the Ditsong Museum of Natural History)

About 600,000 years ago, our common ancestor and the progenitor of both Neanderthals and Denisovans diverged from the common ancestor. This presumably occurred in Africa. They extended into Eurasia, where the Denisovans migrated east and the Neanderthals moved west as they travelled over the continent. Both populations died out around 40,000 years ago and have not been seen since.

During this time period, modern humans were developing their traits in Africa. They eventually moved into Eurasia, where they interbred with Neanderthals as well as Denisovans after arriving there. At the present time, every human being alive carries a little amount of Neanderthal DNA. In addition, people from New Guinea and the regions that surround it as well as Aboriginal Australians have been found to contain the Denisovan DNA.

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The researchers investigated how new gene variants emerged in each distinct branch of the human family tree. The majority of the results were consistent with the theories that are now being proposed regarding human evolution. However, among the populations in West Africa, such as the Yoruba of Nigeria and the Mende of Sierra Leone, part of the DNA included mutations that are not seen in other living humans or even in Neanderthals or Denisovans. These variants were unique to these West African populations. “What it told us was that this was not a simple story,” Dr. Sankararaman said.

A small percentage of the DNA found in surviving West Africans appeared to have originated in an ancient human lineage that was not Homo sapiens or any other species in our genus whose genetic makeup is known from other species’ genes. According to the model developed by Mr. Durvasula and Dr. Sankararaman, this ghost archaic population diverged from the lineage that eventually gave rise to modern humans, Neanderthals, and Denisovans at least one million years ago.

Intriguingly, this occurred around the same time that modern humans in Eurasia also interbred with Neanderthals and Denisovans. They estimated that the ancestors of West Africans and the ghost archaic population interbred approximately 50,000 years ago.

The researchers were unable to determine what species of human beings the Ghost archaic population comprised. The fossil record in Africa only provides a few suggestions about the history of the continent. There was a species known as Homo erectus that lived in Africa one million years ago. Morocco is the location of the oldest fossils of Homo sapiens, which date back 300,000 years. However, researchers have also discovered an impressive variety of additional fossils belonging to our genus that were uncovered in Africa during that time period.

ghost dna west africa
‘Benin Bronze’ plaque showing the king (Oba) in regalia (West Africa) and with symbols of royal power (c.16th–17th century). Credit: British Museum

At a site in Nigeria known as Iwo Eleru, archaeologists have discovered a human skull that dates back just 11,200 years. It is one of the most remarkable discoveries. The initial scholars who investigated the remains established a connection between them and living people from West Africa. But in 2011, a group of researchers looked at the skull of Iwo Eleru with greater scrutiny and came to the conclusion that it belonged to an intermediate species of Homo between modern humans and Homo erectus.

Both Mr. Durvasula and Dr. Sankararaman have posed the possibility that fossils such as Iwo Eleru belonged to an extinct archaic ghost population. “It is indeed possible,” said Isabelle Crevecoeur, a paleoanthropologist at the University of Bordeaux in France. However, she emphasized that before jumping to such a definitive conclusion, scientists still needed to discover a great deal more about the physical and genetic diversity of people who were of African descent. “I would favor a conservative approach,” she said.

Similarly, according to the findings of a scientific study published in 2016, it is possible that modern-day Melanesians’ DNA contains traces of a long-extinct and yet unknown human species. The nations of Vanuatu, the Solomon Islands, Fiji, and Papua New Guinea, in addition to a few smaller islands, may be found in the region known as Melanesia, which can be found in the South Pacific Ocean to the northeast of Australia.

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