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Complex admixture history of early humans

When scientists look at the genes of Neanderthals, various genomic studies suggest that anatomically modern humans and Neanderthals likely interbred, and that the resulting male children may have had reduced fertility. The females most likely were fertile and to have children would have had to mate with Homo Sapiens or full Neanderthals instead of the hybrid males who were half Neanderthal and half Homo Sapien. This site of Kostenki Man re-creation shows how people (Homo Sapien) living 30,000 to 39,000 years ago might have looked. His mother's DNA (mtDNA) was the very Homo Sapien U2. He lived in Russia, in the area known as Kostenki. And here's a website showing a re-creation of a Neanderthal child based on restoration of some of the bones.

Complex admixture history of early humans.
Photo by Mark Mainz/Getty Images

A modern person of current times would be too far apart genetically to admix with a Neanderthal, if any were around today. But a prehistoric Homo Sapien of 60,000 years ago, more likely would have been on the border of being able to admix with a Neanderthal, and the two may have interbred somewhere in the Middle East before the children of Neanderthals and Homo Sapiens migrated to Europe.

Neanderthals were not inferior to modern humans, says University of Colorado at Boulder (CU-Boulder) study, "'Neandertal Demise: An Archaeological Analysis of the Modern Human Superiority Complex," published online , 2014 in the journal PLOS ONE .

Neanderthals and Denisovans aren't the only types that admixed with Homo Sapiens, according to genetic testing, says the study, "Genome-wide Scan of Archaic Hominin Introgressions in Eurasians Reveals Complex Admixture History," published online May 1, 2014 in Populations and Evolution

Noteworthy is that scientists call admixture introgressions, as if the word connoted some type of trespassing instead of simply mating and admixing. The abstract of that paper explains that introgressions from Neanderthals and Denisovans were detected in modern humans. Introgressions from other archaic hominins were also implicated, however, identification of which poses a great technical challenge.

What the study is aiming at is that two other unknown types or archaic people mixed genes with the line that led to Homo Sapiens, but probably at a time long before Neanderthals admixed with Homo Sapiens. The study explains that the researchers introduced an approach in identifying introgressions from all possible archaic hominins in Eurasian genomes, without referring to archaic hominin sequences.

The researchers focused on mutations emerged in archaic hominins after their divergence from modern humans (denoted as archaic-specific mutations), and identified introgressive segments which showed significant enrichment of archaic-specific mutations over the rest of the genome

Furthermore, boundaries of introgressions were identified using a dynamic programming approach to partition whole genome into segments which contained different levels of archaic-specific mutations. Researchers in that study found that detected introgressions shared more archaic-specific mutations with Altai Neanderthal than they shared with Denisovan, and 60.3% of archaic hominin introgressions were from Neanderthals. So from where did the other nearly 40% of admixtures come? Those admixtures of genes came from two unknown archaic hominins.

The researchers explain in the study's abstract that they detected more introgressions from two unknown archaic hominins that diverged with modern humans approximately 859,000 and 3,464,000 years ago. That's a long time ago. But scientists still can find the DNA or the genome of someone who existed at that time showing up in modern people, and they can compare those genes to remains that old...3,464,000 years ago. Noteworthy, it's the person who lived more than three million years ago whose genes now show up in everyone living today.

How many generations is that to find the first person who admixed with someone leading to the branch that led to modern people around the world? And why did the genes of that more than three million-year old branch persist in humans of today, but the branch that existed 859,000 years ago didn't pass his or her genes on to people living today?

The latter unknown archaic hominin contributed to the genomes of the common ancestors of modern humans and Neanderthals.

In total, archaic hominin introgressions comprised 2.4% of Eurasian genomes. Above results suggested a complex admixture history among hominins. The proposed approach could also facilitate admixture research across species.

It's noteworthy to imagine how many different archaic peoples left their genes in people of today, and those genes still can be found and studied. Now the question is who was the first individual to contribute genes of everyone alive today so that those old genes not only can be detected, but also studied to see how many different archaic individuals are in everyone's bodies in current times? And how far back in years can scientists detect those genes in what's known as the autosomal DNA? Then again, what's the function of those archaic genes in modern people?

If you think Neanderthals were stupid and primitive, it's time to think again

The widely held notion that Neanderthals were dimwitted and that their inferior intelligence allowed them to be driven to extinction by the much brighter ancestors of modern humans is not supported by scientific evidence, according to a researcher at the University of Colorado Boulder.

Neanderthals thrived in a large swath of Europe and Asia between about 350,000 and 40,000 years ago. They disappeared after our ancestors, a group referred to as "anatomically modern humans," crossed into Europe from Africa.

In the past, some researchers have tried to explain the demise of the Neanderthals by suggesting that the newcomers were superior to Neanderthals in key ways, including their ability to hunt, communicate, innovate and adapt to different environments

In an extensive review of recent Neanderthal research, CU-Boulder researcher Paola Villa and co-author Wil Roebroeks, an archaeologist at Leiden University in the Netherlands, make the case that the available evidence does not support the opinion that Neanderthals were less advanced than anatomically modern humans. Their paper was published today in the journal PLOS ONE.

"The evidence for cognitive inferiority is simply not there," said Villa, according to the April 30, 2014 news release, "Neanderthals were not inferior to modern humans, says CU-Boulder study." Villa is a curator at the University of Colorado Museum of Natural History. "What we are saying is that the conventional view of Neanderthals is not true."

Villa and Roebroeks scrutinized nearly a dozen common explanations for Neanderthal extinction that rely largely on the notion that the Neanderthals were inferior to anatomically modern humans. These include the hypotheses that Neanderthals did not use complex, symbolic communication; that they were less efficient hunters who had inferior weapons; and that they had a narrow diet that put them at a competitive disadvantage to anatomically modern humans, who ate a broad range of things.

The researchers found that none of the hypotheses were supported by the available research.

For example, evidence from multiple archaeological sites in Europe suggests that Neanderthals hunted as a group, using the landscape to aid them. Researchers have shown that Neanderthals likely herded hundreds of bison to their death by steering them into a sinkhole in southwestern France. At another site used by Neanderthals, this one in the Channel Islands, fossilized remains of 18 mammoths and five woolly rhinoceroses were discovered at the base of a deep ravine. These findings imply that Neanderthals could plan ahead, communicate as a group and make efficient use of their surroundings, the authors said, according to the news release.

Other archaeological evidence unearthed at Neanderthal sites provides reason to believe that Neanderthals did in fact have a diverse diet. Microfossils found in Neanderthal teeth and food remains left behind at cooking sites indicate that they may have eaten wild peas, acorns, pistachios, grass seeds, wild olives, pine nuts and date palms depending on what was locally available.

Additionally, researchers have found ochre, a kind of earth pigment, at sites inhabited by Neanderthals, which may have been used for body painting. Ornaments have also been collected at Neanderthal sites. Taken together, these findings suggest that Neanderthals had cultural rituals and symbolic communication.

Villa and Roebroeks say, according to the news release, that the past misrepresentation of Neanderthals' cognitive ability may be linked to the tendency of researchers to compare Neanderthals, who lived in the Middle Paleolithic, to modern humans living during the more recent Upper Paleolithic period, when leaps in technology were being made

"Researchers were comparing Neanderthals not to their contemporaries on other continents but to their successors," Villa said, according to the news release. "It would be like comparing the performance of Model T Fords, widely used in America and Europe in the early part of the last century, to the performance of a modern-day Ferrari and conclude that Henry Ford was cognitively inferior to Enzo Ferrari."

Although many still search for a simple explanation and like to attribute the Neanderthal demise to a single factor, such as cognitive or technological inferiority, archaeology shows that there is no support for such interpretations, the authors said, according to the news release. But if Neanderthals were not technologically and cognitively disadvantaged, why didn't they survive?

The researchers argue that the real reason for Neanderthal extinction is likely complex, but they say some clues may be found in recent analyses of the Neanderthal genome during the last several years

These genomic studies suggest that anatomically modern humans and Neanderthals likely interbred and that the resulting male children may have had reduced fertility. Recent genomic studies also suggest that Neanderthals lived in small groups. All of these factors could have contributed to the decline of the Neanderthals, who were eventually swamped and assimilated by the increasing numbers of modern immigrants.

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