DNA Results Stun Researchers

Many family researchers, genealogists and others are taking DNA tests today to trace their ancestry and learn more about their genetic origins. For some, the results are a confirmation of what they already suspected; for others, it may be a total surprise.    

Imagine your DNA test results come back and you discover you are half Neanderthal and half Denisovan. Well, if your name is Denny, a female who died around 90,000 years ago in a remote Siberian cave, that’s exactly what the test results showed.  

An artist’s impression of the teenage Denny. Photograph: John.Bavaro/early-man.com

Paleontologists never thought they would find an integrated species between two of humanity’s early relatives. But there’s no mistake here. These remains come from a girl whose parents were from two entirely different species.

Denny’s bone fragment was found in the Denisova Cave in the Altia Mountains of Russia. Both Denny and the cave are named after the Denisovans, a group of extinct humans.

Enjoy a quick tour Inside the Denisova Cave.

YouTube video by the Siberian Times.

Because of genetic variations in ancient and modern humans, scientists long suspected Neanderthals and Denisovans must have mated with each other and with Homo sapiens, but until now, no first-generation off-spring had been found. 

I guess you can call this… one tangled family tree. 

Against All Odds

The odds of making this discovery seem insurmountable. First, it took a group of Russian anthropologists searching a Siberian cave to unearth and collect the tiny bone fragment; next, the fossil went to storage for later identification, where it languished in obscurity for several years along with 2,000 other unidentified fragments thought to be animal; then it took the keen eye of a highly skilled paleontologist to identify this fragment as human, rather than animal; and miraculously, the bone contained enough DNA to be extracted and sequenced.

Denny’s bone fragment, 1st generation Neanderthal and Denisovan species, discovered by Viviane Sion and Savante Paabo of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany

The find consisted of a single bone fragment from either a human arm or leg, that prior to genetic testing weighed 0.059 oz, and its maximum dimensions were 0.97” long and 0.330” wide.

Dating analysis of the bone was performed in 2016, and it was determined this individual died about 90,000 years ago, and based on the bone’s thickness it was concluded the person was at least 13 years old. 

Other fossils found in this Siberian cave have previously shown that all three species, modern human, Neanderthal and Denisovan lived there at different times. 

After the bone fragment was dated, it was sent to the Max Planck Institute for Evolutionary Anthropology in Leipeig, Germany, an institution where Denisovan DNA had been previously isolated and sequenced. In 2018, the first analysis was done of Denny’s mitochondrial DNA, which was followed by testing of her nuclear DNA.   

Soon after the DNA analysis, an incredible story began to unfold— findings that would turn decades of research on its head and reveal some new truths about the human race and how ancient peoples made their way in the world.

Prehistoric Human Ancestry

Before we dive deeper into the significance of Denny’s results, this is a good time for a quick primer on prehistoric human ancestry so we can understand how Denny fits into the human progression. 

Today, all people belong to the same species, Homo sapiens, which first emerged approximately 200,000 to 300,000 years ago, evolving from their early hominin predecessors.

The original complete skull, without upper teeth and mandible of a 2.1 million years old Australopithecus africanus specimen so-called “Mrs. Ples” discovered in South Africa, photo credit Jose Braga and Didier Descouens

The earliest known human ancestors were the Australopithecus species, which includes a number of different subgroups capable of both climbing and walking on two legs. According to research, these distant relatives of Homo sapiens first emerged in Africa around 4.2 million years ago. Of course, they would have looked different from how we appear today, they shared several traits with modern apes and humans, and were widespread throughout Eastern and Northern Africa. 

Next, scientists believe, the various species of Homo began to emerge. At first, they evolved longer legs, which were better suited to running and walking. Their brains were also larger. These adaptations allowed for changes in behavior, such as hunting and consuming a more carnivorous diet.

Reconstructed skull at the National Museum of Natural History.

Then, about 700,000 years ago, the species known as Homo heidelbergensis emerged in Africa and Eurasia. Remains have been discovered in: Sima de los Hueso, Spain: Jinniushan, China; and Kabwe, Zambia. 

Experts suggest these hominins were much more like modern people in their appearance, laying the groundwork for how their descendants would evolve.

Scientists believe that Homo heidelbergensis were more intelligent than those who had come before them. Their brain size was larger and comparable to modern humans. This species used advanced tools and honed their hunting techniques. Fire likely became an integral part of daily life after 400,000 years ago. It is also believed that individuals may have grouped together to bring down larger animals, which indicates a degree of social organization and bonding. But, despite their attributes, the species would eventually die out.

However, Homo heidelbergensis simply didn’t disappear from the planet without leaving a trace. An estimated 390,000 years ago, in the Middle Pleistocene era, a number of different species began to split off from this common ancestor. And from these branches, modern humans would ultimately emerge.

Homo sapiens, the first modern humans and all of us, emerged between 200,000 and 300,000 years ago. They developed a capacity for language about 50,000 years ago. Starting 100,000 to 70,000 years ago, the first modern humans began moving outside of Africa. Until 12,000 years ago, all humans lived as hunter-gatherers. Homo sapiens are often characterized by our abilities to make advanced tools, our language skills, and complex social and cultural structures.

Interspecies Living

The history of humankind is one of a progression. For years, research has suggested that some species of hominin coexisted with one another over the millennia, and some degree of interbreeding must have taken place between these different groups, which produced healthy offspring. But, until Denny’s discovery, no one could prove this for sure.

Early humans are believed to have shared the same number of chromosomes, which meant the different species were able to interbreed. Experts believe that Homo sapiens began mating with Homo Neanderthals not long after migrating from Africa and spreading out around the world. That’s why most modern humans from Asia and Europe have about 2 percent Neanderthal DNA. Perhaps you noticed this in your own genetic test? 

Neanderthals, Field Museum, Chicago

But now we know that Homo sapiens weren’t just coupling with Neanderthals. Apparently, members of the species also mated with the Denisovans.

The Denisovans are a fairly recent discovery in the field of evolutionary studies. In 2010, a team of scientists from the Max Planck Institute announced they had found evidence of a new species of early human after analyzing a tooth and a finger bone found in the Altai Mountains in Siberia. Researchers dubbed the species Denisova in honor of the cave in which the specimens were found.

But aside from what could be interpreted from DNA, little was known about this human ancestor.  Up to 6% of the genes now found in modern New Guineans and 3-5% of the DNA of aboriginal Australians is made up of Denisovan DNA. The gene that permits Tibetans to survive in high altitudes is also believed to have been inherited from the Denisova.

Denny’s DNA Testing

At first, Denny’s bone fragment did not appear to be anything remarkable. But when the DNA was analyzed, scientists were in for a Big Surprise. 

Mitochondrial DNA (mtDNA) contains material that a child inherits only from their mother. And in this case, mtDNA analysis indicated that the girl descended from a female Neanderthal, who was genetically closer to Western European Neanderthals than earlier Neanderthals who lived in the Denisova Cave. That suggested some Neanderthals migrated from Western Europe to Central Eurasia tens of thousands of years before the species died out. 

While this initial result was already intriguing, it got more exciting when they looked at the bone’s nuclear DNA. Nuclear DNA is passed down through both the male and female lines, so scientists were able to learn more about the ancient teenager’s father.

That’s when it was realized that something was unusual about this bone. In fact, the results were so shocking that the scientist performing the test was convinced she had made a mistake or the sample had been contaminated in the laboratory. 

Eventually, though, she realized it wasn’t a mistake… Denny’s father, according to the nuclear DNA analysis, had been a Denisovan. And that wasn’t all!

While analyzing the bone fragment, the paleogeneticist discovered that the girl’s genetic makeup was an unique variant…it was highly heterozygous. Okay, what does that mean? 

Simply put, if your parents are closely related (like second cousins) the amount of heterozygosity present in your genes would be relatively small. On the other hand, if you were the result of inter-species breeding, those levels would be sky-high. And with Denny’s bone, it was definitely a case of the latter. That confirmed she was a first-generation child born of interbreeding between species.

This discovery is amazing and now raises the question of how common interbreeding among species occurred, which may be more often than originally thought. Perhaps the two species actually interacted and interbred with each other on a more regular basis, despite the fact that they lived mainly in separate territories – the Neanderthals in Europe and Denisovans in east Asia. And if this theory is true, it would turn our previous understanding of the ancient world on its head.

Article References

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