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Do you remember those school science posters that depicted human evolution with a primate standing up and becoming a modern human? Of course you do, but you may not have noticed that these posters never showed any years - and that is because until this new scientific paper scientists were unclear about when, where, and how we mated our way out of Africa. But now, fossilized genes have demonstrated that some of our ancestors, referred to as “super archaic” humans, mated with Neanderthal and Denisovan ancestors, a long, long time ago.
Several new scientific studies have suggested the ancestors of all three groups had mixed at least twice and evidence has been provided of even older “ghost lineages,” from unknown extinct hominins . These new studies greatly lean on models of inheritance and population mixing, showing a confused pattern with the identities of our ancestors’ ancient mates remaining unknown, and precisely when and where these sexual encounters took place ‘was’ a long standing scientific mystery. Until now.
Super-Archaic Humans Got Down With Neanderthal-Denisovan Ancestors
In an article published on Science Mag computational biologist Murray Cox of Massey University of New Zealand, Turitea said that when interpreted together, as a whole, the new paper presents a strong case that before Homo erectus left Africa, as early as 1.8 million years ago, they were interbreeding with different groups. Furthermore, long after they had spread around the world they mated with later waves of human ancestors leaving Africa.
Anthropologist Alan Rogers of the University of Utah has spent three years trying to solve the mystery of human evolution by compiling a detailed comparative analysis of DNA strands from ancient hominins which highlights genetic mutations and shared genes in ancient human populations. Dr. Rogers’ 2017 study proved that two lineages of ancient humans, “Neanderthals and Denisovans,” had separated much earlier than previously thought and he proposed a bottleneck in population sizes had occurred; but anthropologists Mafessoni and Prüfer published a paper on PNAS with different results.
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A population network including four episodes of gene flow, with an embedded gene genealogy. ( Rogers, Harris, and Achenbach ) Upper case letters ( X, Y, N, D, and S) represent populations (Africa, Europe, Neanderthal, Denisovan, and superarchaic). Greek letters label episodes of admixture.
Rogers conceded that neither study had explained the genetic data satisfactorily and both methods were missing something essential, but his new study has now solved the problem. The new paper was published on Feb. 20, 2020 in the journal Science Advances and demonstrates the earliest known interbreeding event in Eurasia between ancient human populations known as the “super-archaics” with a Neanderthal-Denisovan ancestor – occurred about “700,000 years ago.”
Reconstruction of Homo rhodesiensis based on the Broken Hill cranium, by Élisabeth Daynès (2010), Museum of Human Evolution, Burgos. ( CCO)
Applying a new method for analyzing ancient DNA Dr. Rogers’ latest paper proves a mating event occurred between two populations that were “more distantly related than any other ever recorded,” and that scientists never knew about this early episode of interbreeding. Four proposed episodes of gene flow point to the hitherto unknown event some 744,372 years ago, suggesting interbreeding had taken place between super-archaics and Neanderthal-Denisovan ancestors “in Eurasia,” which suggests the timeline for humans migrating out of Africa and into Eurasia needs revision.
It is known that modern humans and Neanderthals had been separated for about 750,000 years when they started interbreeding and the super-archaics and Neanderthal-Denisovan ancestors were separated for well over a million years. These new findings, about the timing at which interbreeding happened in the human lineage, informs about how long it takes “for reproductive isolation to evolve,” said Rogers.
Drawing of a Neandertal mother and a Denisovan father with their child, a girl, at Denisova Cave in Russia. ( Petra Korlević )
Our Dangerous Genetic Situation
Studying genomes, the team of genetic scientists estimated that the super-archaic separated into its own species about two million years ago, which is supported with human fossil evidence in Eurasia that dates to 1.85 million years old. Nathan S. Harris and Alan A. Achenbach from the Department of Anthropology at the University of Utah, who also contributed to the study, said the first two human migrations into Eurasia occurred about two million years ago when the super-archaics migrated into Eurasia and subsequently expanded into a large population.
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It was about 700,000 years ago that Neanderthal-Denisovan ancestors migrated into Eurasia and began interbreeding with descendants of super-archaics and modern humans, who only expanded to Eurasia 50,000 years ago and bred with the Neanderthals.
Neanderthal. ( procy_ab / Adobe Stock)
All of these diverse and varied breeding patterns that you have just read about cannot ever happen again, as today Homo sapiens are the only humans on the planet and even if we fancied a try, there are no other mating options. This, according to geneticist Carina Schlebusch of Uppsala University, is not a healthy situation - we have such a large densely spread species with so little genetic diversity , which she says “is a dangerous situation”.
The 'Ghost' of an Unknown Extinct Human Has Been Found in DNA of Modern West Africans
The gene pool of modern West Africans contains the 'ghost' of a mysterious hominin, unlike any we've detected so far. Similar to how humans and Neanderthals once mated, new research suggests this ancient long-lost species may have once mingled with our ancestors on the African continent.
Using whole-genome data from present-day West Africans, scientists have found a small portion of genetic material that appears to come from this mysterious lineage, which is thought to have split off from the human family tree even before Neanderthals.
Today, it's thought (although still being debated) that anatomically modern humans originated in Africa, and that once these populations migrated to Europe and Asia, they interbred with closely-related species like Neanderthals and Denosovans.
As such, modern West Africans, like populations in Yoruba and Mende, do not possess genes from either of these ancient species, but that doesn't mean there was no intermixing. In fact, recent evidence suggests the genetic past of West Africans may contain a similarly juicy narrative.
The idea is hard to confirm, because ancient human remains and DNA are scarce on the African continent and even harder to find in West Africa.
Fortunately there is one way to get an idea of how ancient humans mixed that doesn't involve studying remains: modern genomics. Researchers decided to compare 405 modern genomes from the Yoruba and Mende populations with genomes from Neanderthals and Denisovans.
To their surprise, they also found traces of another as-yet-unknown ancient hominin species in their genomes.
Similar to how modern humans outside of Africa still hold traces of Neanderthal genes, the authors found populations in West Africa derived between 2 and 19 percent of their genetic ancestry from this as-yet-undiscovered ancient hominin.
Interestingly, this isn't the first time 'ghost' species of unknown extinct ancestors have been found in modern DNA. Researchers looking at Eurasian DNA have previously found traces of at least three as-yet-undiscovered ancient hominins in modern human genomes. But this is a first for modern West African DNA.
The findings are supported by several other studies that suggest there have been multiple interbreeding events between archaic and modern human populations in Africa.
This is known as genetic introgression, but while it's become a popular theory, exactly where, when and to what extent this mixing occurred is unknown.
In the fossil record, modern humans show up around 200,000 years ago, but in parts of sub-Saharan Africa, a few fossils have been found with a mix of archaic and modern features that are only 35,000 years old.
"One interpretation of the recent time of introgression that we document is that archaic forms persisted in Africa until fairly recently," the authors of the new study suggest.
"Alternatively, the archaic population could have introgressed earlier."
In the end, neither is mutually exclusive, but the authors say we will need more analysis of African genomes across the continent before we can understand the true makeup of our ancestors.
'Ghost' DNA In West Africans Complicates Story Of Human Origins
An artist's rendering of DNA. Scientists have found traces of DNA that they say is evidence that prehistoric humans procreated with an unknown hominin group in West Africa. Westend61/Getty Images/Westend61 hide caption
An artist's rendering of DNA. Scientists have found traces of DNA that they say is evidence that prehistoric humans procreated with an unknown hominin group in West Africa.
About 50,000 years ago, ancient humans in what is now West Africa apparently procreated with another group of ancient humans that scientists didn't know existed.
There aren't any bones or ancient DNA to prove it, but researchers say the evidence is in the genes of modern West Africans. They analyzed genetic material from hundreds of people from Nigeria and Sierra Leone and found signals of what they call "ghost" DNA from an unknown ancestor.
Our own species — Homo sapiens — lived alongside other groups that split off from the same genetic family tree at different times. And there's plenty of evidence from other parts of the world that early humans had sex with other hominins, like Neanderthals.
That's why Neanderthal genes are present in humans today, in people of European and Asian descent. Homo sapiens also mated with another group, the Denisovans, and those genes are found in people from Oceania.
Denisovans, A Mysterious Kind Of Ancient Humans, Are Traced To Tibet
The findings on ghost DNA, published in the journal Science Advances, further complicate the picture of how Homo sapiens — or modern humans — evolved away from other human relatives. "It's almost certainly the case that the story is incredibly complex and complicated and we have kind of these initial hints about the complexity," says Sriram Sankararaman, a computational biologist at UCLA.
The scientists analyzed the genomes of 405 West Africans. Sankararaman says they used a statistical model to flag parts of the DNA. The technique "goes along a person's genome and pulls out chunks of DNA which we think are likely to have come from a population that is not modern human."
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The unusual DNA found in West Africa isn't associated with either Neanderthals or Denisovans. Sankararaman and his study co-author, Arun Durvasula, think it comes from a yet-to-be-discovered group.
"We don't have a clear identity for this archaic group," Sankararaman says. "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."
The scientists think the interbreeding happened about 50,000 years ago, roughly the same time that Neanderthals were breeding with modern humans elsewhere in the world. It's not clear whether there was a single interbreeding "event," though, or whether it happened over an extended period of time.
The unknown group "appears to have split off from the ancestors of modern humans a little before when Neanderthals split off from our ancestors," he says.
Sharon Browning, a biostatistics professor at the University of Washington who has studied the mixing of Denisovans and humans, says "the scenario that they are discovering here is one that seems realistic."
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Browning notes that the ghost DNA appears frequently in the genetic material. "That tells us that these archaic populations might have had some DNA that did some useful stuff that's proved to be useful to the modern population," she says.
But at the moment, Sankararaman says, it's not possible to know what, if any, role these genetic materials have for modern humans who carry them. "Are they just randomly floating in our genomes? Do they have any kind of adaptive benefits? Do they have deleterious consequences?" he added. "Those are all questions which would be fantastic to start thinking about."
He says there is likely evidence of other ghost populations in modern humans in other parts of the world. "I think as we get the genome sequences from different parts of the world at different points in time, there is always the possibility that we might discover these as-yet-unidentified ghost populations," Sankararaman says.
It's also possible that the ghost DNA found in this study comes from multiple groups, Browning added. "Within Africa, we don't know how many archaic groups might have been involved, and the study doesn't tell us that," she says. "It tells us that there was integration, but it could have been from more than one archaic population, in theory."
Compared with the Neanderthals, where there is abundant DNA fossil evidence, physical samples are much harder to come by in Africa. Browning says the climate on the continent has made it challenging.
"The conditions have to be right for the fossils to not totally disintegrate" in order to recover DNA, Browning says. Bones have been found in Africa from archaic populations, but no DNA has been recovered. Still, she adds, "the technology is continuing to improve, and people are still out there looking for more fossils."
So what happened to this mysterious group of ancient humans? Scientists aren't totally sure.
They might have died off, or they might have eventually been completely subsumed into modern humans.
A number of varieties of Homo are grouped into the broad category of archaic humans in the period that precedes and is contemporary to the emergence of the earliest early modern humans (Homo sapiens) around 300 ka. Omo-Kibish I (Omo I) from southern Ethiopia (196 ± 5 ka)  and the remains from Jebel Irhoud in Morocco (about 315 ka) and Florisbad in South Africa (259 ka) are among the earliest remains of Homo sapiens.       The term typically includes Homo neanderthalensis (430+–25 ka),  Denisovans, Homo rhodesiensis (300–125 ka), Homo heidelbergensis (600–200 ka), Homo naledi, Homo ergaster, and Homo antecessor.
There is no universal consensus on this terminology, and varieties of "archaic humans" are included under the binomial name of either Homo sapiens or Homo erectus by some authors.
Archaic humans had a brain size averaging 1,200 to 1,400 cubic centimeters, which overlaps with the range of modern humans. Archaics are distinguished from anatomically modern humans by having a thick skull, prominent supraorbital ridges (brow ridges) and the lack of a prominent chin.  
Anatomically modern humans appear around 300,000 years ago in Africa,       and 70,000 years ago (see Toba catastrophe theory), gradually supplanting the "archaic" human varieties. Non-modern varieties of Homo are certain to have survived until after 30,000 years ago, and perhaps until as recently as 12,000 years ago. Which of these, if any, are included under the term "archaic human" is a matter of definition and varies among authors. Nonetheless, according to recent genetic studies, modern humans may have bred with "at least two groups" of ancient humans: Neanderthals and Denisovans.  Other studies have cast doubt on admixture being the source of the shared genetic markers between archaic and modern humans, pointing to an ancestral origin of the traits which originated 500,000–800,000 years ago.   
Another group may also have been extant as recently as 11,500 years ago, the Red Deer Cave people of China.  Chris Stringer of the Natural History Museum in London has suggested that these people could be a result of mating between Denisovans and modern humans.  Other scientists remain skeptical, suggesting that the unique features are within the variations expected for modern human populations. 
Neanderthal-Denisovan Ancestor Canoodled With Mystery Group Of "Super-Archaic" Humans
There could be yet another new character in the story of human evolution – and even more evidence of hanky panky within our evolutionary family.
A new study suggests that the ancestors of Neanderthals and Denisovans, two of Homo sapiens’ closest cousins, interbred with a mysterious population of their own Eurasian predecessors 700,000 years ago, and it's the earliest interbreeding between ancient human populations we know of yet.
It’s unclear “who” these hominins were, but they are known to be members of a “super-archaic” population that separated from other humans about 2 million years ago. By the researchers' workings, this population was made up of as many as 20,000 to 50,000 individuals.
"We aren't sure who the super-archaics were. They may have been Homo erectus, or Homo antecessor, or some other taxon that has not been named," lead author Alan Rogers, a professor in the Department of Anthropology at the University of Utah, told IFLScience.
"I suspect they were Eurasian, but a recent paper out of Sriram Sankararaman's lab finds evidence of super-archaic admixture in west Africa. In future research, it will be interesting to find out whether our super-archaics were the same as Sriram's," he said.
All of this might sound a bit hazy, but the evolutionary history of the Homo family is filled with many gaps in our knowledge and plenty of confusing interlinked plot points. We know that humans, Neanderthals, and Denisovans all widely interbred with each other on multiple historic occasions. However, other researchers have also found that our genetics contain the "ghosts" of many other large-brained hominins that we've never discovered the remains of.
"It seems very clear that our family tree wasn't really a tree at all it was more of a network. In the middle Pleistocene, there were apparently several hominin populations that had been separate for a long time but could still interbreed," Rogers added.
An evolutionary tree including four proposed episodes of gene flow. The previously unknown event 744,372 years ago (orange) suggests interbreeding occurred between super-archaics and Neanderthal-Denisovan ancestors in Eurasia. Adapted from Alan Rogers
Reporting in the journal Science Advances, the researchers reached these findings using computer modeling software that uses genetic data to understand the history of populations and the flow of DNA between them. The research gathered data from Neanderthals found in the Altai Mountains of Siberia and the Vindija Cave in Croatia, as well as from modern Europeans, then looked to understand how the various genetic combinations might have emerged using different models.
This novel software method did not just reveal some insights into Neanderthal-Denisovan ancestors interbreeding with a distantly related hominin, it has also helped to shed light onto some of the murkier chapters of the human story. In 2017, this same project argued that Neanderthals split from Denisovans about 381,000 years ago. However, the new software found that the split was much earlier, suggesting that Neanderthals were already distinct from Denisovans 600,000 years ago
One of the big questions surrounding modern humans is the many waves of early human migrations out of Africa and into Eurasia. As per the new study, modern humans and their ancestors migrated from Africa into Eurasia in just three main waves: 1.9 million years ago, 700,000 years ago, and 50,000 years ago.
They also showed plenty more evidence that Neanderthals interbred with the ancestors of modern humans. However, that's no surprise if you take a look at own our DNA. It's long been clear that most people of European descent have some Neanderthal genes in their genome, but research released in January of this year showed that traces of Neanderthal DNA can be found in almost every modern population on Earth, even those living in Africa, where it's understood Neanderthals never stepped foot.
'Ghost population' of ancient humans may have mated with ancestors of modern humans
Researchers believe these spear points they dug up are the oldest weapons ever discovered in North America. The findings raise new questions about where the first humans in the Americas settled. USA TODAY
Ancestors of people living in what is today West Africa may have reproduced with a species of ancient humans unknown to scientists, new research suggests.
Scientists know Europeans mated with Neanderthals and people in Oceania with Denisovans, but a new study published Wednesday in the peer-reviewed journal Science Advances found that genetic variation within West African populations is best explained by the presence of a new ancient human species altogether.
With difficulties in obtaining a full fossil records and ancient DNA, scientists' understanding of the genetic diversity within West African populations has been poor. To get a fuller picture, researchers at University of California, Los Angeles compared 405 genomes of West Africans with Neanderthal and Denisovan genomes.
Sriram Sankararaman, one of the study's authors, told NPR that the researchers used statistical modeling to figure out which parts of the DNA they were analyzing did not come from modern humans, then compare those to the two ancient hominin species. What they found is the presence of DNA from "an archaic ghost population" in modern West African populations' genetic ancestry.
"We don't have a clear identity for this archaic group," Sankararaman told NPR. "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."
Sankararaman and co-author Arun Durvasula found this introgression, or sharing of genetic information between two species, between the "ghost population" and ancestors of West Africans may have occurred within the last 124,000 years. The "ghost population" likely split from humans and Neanderthals into a new species between 360,000 to 1.02 million years ago, the study says.
The study also says the breeding may have occurred over an extended period of time, rather than all at once.
"It's very likely that the true picture is much more complicated," Sankararaman told the Guardian.
John Hawks, an anthropologist at the University of Wisconsin-Madison, told the newspaper that studies like this one, "Open a window showing us that there is much more than we thought to learn about our ancestors."
"Actually knowing who those ancestors were, how they interacted, and where they existed is going to take fieldwork to find their fossil and archaeological remains," he told the Guardian. Hawks was not involved in the study.
This interbreeding may also have a great impact on the genetic makeup of modern populations: Anywhere from 2% to 19% of their genetic ancestry could be derived from the "ghost population."
However, whether that affects modern day people will require further research, Sankararaman says.
"Are they just randomly floating in our genomes? Do they have any kind of adaptive benefits? Do they have deleterious consequences?" he told NPR.
'Ghost' ancestors: African DNA study detects mysterious human species
WASHINGTON (Reuters) - Scientists examining the genomes of West Africans have detected signs that a mysterious extinct human species interbred with our own species tens of thousands of years ago in Africa, the latest evidence of humankind’s complicated genetic ancestry.
The study indicated that present-day West Africans trace a substantial proportion, some 2% to 19%, of their genetic ancestry to an extinct human species - what the researchers called a “ghost population.”
“We estimate interbreeding occurred approximately 43,000 years ago, with large intervals of uncertainty,” said University of California, Los Angeles (UCLA) human genetics and computer science professor Sriram Sankararaman, who led the study published this week in the journal Science Advances.
Homo sapiens first appeared a bit more than 300,000 years ago in Africa and later spread worldwide, encountering other human species in Eurasia that have since gone extinct including the Neanderthals and the lesser-known Denisovans.
Previous genetic research showed that our species interbred with both the Neanderthals and Denisovans, with modern human populations outside of Africa still carrying DNA from both. But while there is an ample fossil record of the Neanderthals and a few fossils of Denisovans, the newly identified “ghost population” is more enigmatic.
Asked what details are known about this population, Sankararaman said, “Not much at this stage.”
“We don’t know where this population might have lived, whether it corresponds to known fossils, and what its ultimate fate was,” Sankararaman added.
Sankararaman said this extinct species seems to have diverged roughly 650,000 years ago from the evolutionary line that led to Homo sapiens, before the evolutionary split between the lineages that led to our species and to the Neanderthals.
The researchers examined genomic data from hundreds of West Africans including the Yoruba people of Nigeria and Benin and the Mende people of Sierra Leone, and then compared that with Neanderthal and Denisovan genomes. They found DNA segments in the West Africans that could best be explained by ancestral interbreeding with an unknown member of the human family tree that led to what is called genetic “introgression.”
It is unclear if West Africans derived any genetic benefits from this long-ago gene flow.
“We are beginning to learn more about the impact of DNA from archaic hominins on human biology,” Sankararaman said, using a term referring to extinct human species. “We now know that both Neanderthal and Denisovan DNA was deleterious in general but there were some genes where this DNA had an adaptive impact. For example, altitude adaptation in Tibetans was likely facilitated by a Denisovan introgressed gene.”
Dating analyses in 2016 determined that this individual died about 90,000 years ago, and the bone fragment's characteristics indicate an age of at least 13 years. An analysis of the whole genome sequence (total mitochondrial and nuclear DNA) indicates she was female,   with a Neanderthal mother and a Denisovan father.   While previous analyses of other ancient genomes concluded that Denisovans, Neanderthals, and modern humans interbred during the ice age in Europe and Asia, this find is the most direct evidence yet that various ancient hominins mated with each other and had offspring.   
Other fossils found in this Siberian cave have previously shown that all three species (modern human, Neanderthal and Denisovan) lived there at different times, and that all three human species interbred with each other.   The genes of both archaic human species are present in many people today, which suggests that when these groups met, they actually mixed with each other.   It is not evident if the mating was consensual,  or if the offspring were fertile.  Some of the researchers involved think that this discovery supports the previous notion that Neanderthals and Denisovans may not have undergone extinction, but assimilation into modern human populations. 
The find consists of a single bone fragment about 2 cm long that was unearthed in 2012 by Russian archeologists at the Denisova Cave,  from layer 12 of the East Gallery. The cave is located in Denisova valley, Altai Mountains at Siberia, Russia.   At the time, the origin (species) of the bone fragment was unknown, and it was archived along with other 2,000 non-descript bone fragments from the cave for later identification.  In 2016, Samantha Brown, then an MSc student at the University of Oxford,  was sorting through the thousands of fragments from the cave, studying the proteins in the bones' collagen to figure out what animal species each one was. Using this method, she identified the bone as hominin.    It was dated to about 90,000 years ago, and the bone thickness was used to determine the person's age, which was at least 13 years old. 
At this point, the bone fragment was referred to the Max Planck Institute for Evolutionary Anthropology, that had previously isolated and sequenced Denisovan DNA.  The first analysis done at Max Planck was of her mitochondrial DNA, followed by nuclear DNA. The publication of their results in 2018 was the first direct evidence of interbreeding, and it was called a "landmark find […] that is helping shape our understanding of hominin interactions."  
According to population geneticist Pontus Skoglund from Harvard Medical School, currently at the Francis Crick Institute in London, "To find a first-generation person of mixed ancestry from [Neanderthal and Denisovan groups] is absolutely extraordinary. . It’s really great science coupled with a little bit of luck. It’s a really clear-cut case. I think it’s going to go into the textbooks right away.” 
The bone fragment, identified by the code DC1227 (GenBank Accession = KU131206) or as Densiova 11, is from a human arm or leg.  Prior to extraction of material for genetic analysis, DC1227 weighed 1.68 g (0.059 oz), and had maximum dimensions of 24.7 mm (0.97 in) by 8.39 mm (0.330 in).  In 2016, a team from the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, then used a small portion of the bone to isolate mitochondrial DNA, which was found to be fully Neanderthal, indicating she was the daughter of a Neanderthal woman. 
Subsequently, analysis of the nuclear genome revealed her father to be Denisovan, but with some Neanderthal ancestry.  This genome thus constitutes the first direct evidence for multiple instances of interbreeding between Neandertals and Denisovans. 
Researchers determined the girl’s mother was genetically closer to Western European Neanderthals than earlier Neanderthals who lived in Denisova Cave, suggesting some Neanderthals had migrated from Western Europe to Central Eurasia tens of thousands of years before the species died out.  
The hypothesis of interbreeding, also known as hybridization, admixture or hybrid-origin theory, has been discussed ever since the discovery of Neanderthal remains in the 19th century.  The linear view of human evolution began to be abandoned in the 1970s as different species of humans were discovered that made the linear concept increasingly unlikely. In the 21st century with the advent of molecular biology techniques and computerization, whole-genome sequencing of Neanderthal and human genome were performed, confirming recent admixture between different human species.  In 2010, evidence based on molecular biology was published, revealing unambiguous examples of interbreeding between archaic and modern humans during the Middle Paleolithic and early Upper Paleolithic. It has been demonstrated that interbreeding happened in several independent events that included Neanderthals, Denisovans, as well as several unidentified hominins. Today, approximately 2% of DNA from most Eurasians is Neanderthal, with traces of Denisovan heritage.  Also, 4-6% of the genome of modern Melanesian people is Denisovan.  Denny represents the first time an ancient individual was discovered whose parents belonged to two discrete species of humans, meaning a 50/50 hybrid, which allows for extensive comparative genetic studies.  
Although the narratives of human evolution are often contentious, the discovery of Denny and other discoveries since 2010 show that human evolution should not be seen as a simple linear or branched progression, but a mix of related species.     In fact, "recent genomic research has shown that hybridization between substantially diverged lineages is the rule, not the exception, in human evolution."  Furthermore, it is argued that hybridization was an essential creative force in the emergence of modern humans. 
In January 2019, scientists reported that several types of humans, including Denisovans, Neanderthals and related hybrids, may have inhabited the Denisova Cave in Siberia over thousands of years, but it is unclear whether they ever shared the cave. 
In February 2019, scientists discovered evidence, based on genetics studies using artificial intelligence (AI), that suggest the existence of an unknown human ancestor species, not Neanderthal, Denisovan or human hybrid (like Denny), in the genome of modern humans.  
Ancient rock shelter
Researchers have found countless artifacts and 18 human burials at the Shum Laka rock shelter, which people have used for at least 30,000 years. But the new study focused on the burials of four children, who lived as the Stone Age transitioned into the Metal Age (also called the Stone-to-Metal Age) in western Central Africa.
This included the remains of a 4-year-old boy and a 15-year-old boy found in a double-burial dating to about 8,000 years ago. The researchers also analyzed the DNA of a 4-year-old girl and an 8-year-old boy found in neighboring burials dating to about 3,000 years ago, during the late Stone-to-Metal Age.
Although they lived thousands of years apart, these children were distant cousins, the researchers found. About one-third of their DNA came from ancestors who were more closely related to hunter and gatherers in western Central Africa. The other two-thirds came from an ancient source in West Africa, including a "long lost ghost population of modern humans that we didn't know about before," study senior researcher David Reich, a population geneticist at Harvard University, told Science magazine.
The DNA of these cousins upended a previously held idea. Until now, researchers thought that the Bantu-speaking peoples, which includes several hundred indigenous groups in sub-Saharan Africa, originated in this area of Central Africa, before radiating out across the lower half of Africa, which includes central, western central, eastern and southern Africa. This idea was thought to explain why most of the people from these regions are closely related to each other.
But the new genetic analyses show that's not the case. The inhabitants of Shum Laka were not the ancestors of Bantu-speaking people at least according to the DNA of these four children.
"The finding that the Shum Laka individuals are most related to present day rainforest hunter-gatherers and not ancestors of Bantu-speakers is surprising given that Shum Laka was long considered by archeologist[s] as the site where Bantu-speaker culture [was] developing in situ," Carina Schlebusch, an evolutionary biologist at the University of Uppsala in Sweden, who wasn't involved with the study, told Live Science in an email.
"However, as the authors mentioned in the article, it might be that multiple groups used the site," Schlebusch said. This means that the Bantu's ancestors might have used the site, but it's not shown in these particular burials.