Ancient DNA Reveals A Girl With Parents of Two Different Species
Science has many branches of study in which important questions about life and all its facets are discussed and explored. There’s botany for the study of plants and biology for the study of life more broadly. For the study of human evolution, there’s Paleoanthropology. Since Charles Darwin first proposed the Theory of Evolution, several important discoveries have been made which have each pushed our understanding of the field forward.
Here is one such example. What began as a chance encounter soon became an important finding. The story made its way through various research papers, and eventually, all the way to National Geographic. To this day, this amazing research captivates the hearts and minds of geneticists, archaeologists, and paleoanthropologists all over the world.
While doing their research on fossilized human remains, scientists discovered something that would change our entire view of history: a girl born from two distinctly different species of human beings.
Once the researchers tested and reconfirmed their findings, they realized the significance of their discovery. This little sample of DNA from ancient history had profound implications for the field of Paleoanthropology, and for the history of humanity.
Chances Were Slim – But They Went for It!
The researchers knew that getting to the bottom of this mystery would not be easy, but they were committed to finding the truth. Putting their heads together, they began the task of piecing together a picture of the girl’s background; where she lived, who she was, and where she grew up.
The story began in Siberia when German researchers stumbled upon a tiny fragment of bone. At first, there was nothing remarkable about the piece. But after careful testing and identification, they discovered that it came from a hominin, a term which means “species of human”. But which type of human? The researchers were unable to say. Soon they began to ponder the mysteries of the fragment.
The Story Behind the “Bone”
Due to decay and the ravages of time, the fragment was incredibly frail. Viviane Slon, a well-known paleo-geneticist from the Max Planck Institute for Evolutionary Anthropology, was called in. She took a great deal of care in extracting DNA from this precious artifact.
So, what did they find? After careful analysis, researchers were able to determine exciting facts that shed new light on how ancient people, our distant ancestors, lived during their time. Using this little fragment of bone, they began to piece together a picture of a young girl from ancient times – a young girl with a fascinating heritage.
We all know of the creatures that roamed the Earth thousands of years before modern humans appeared. One of the more famous is the Mammoth. Mammoths are a species of elephant that went extinct about 10,000 years ago. Their trunks were thicker and longer than that of the modern elephant.
As well as studying ancient animals, researchers have uncovered valuable information by studying our ancestors, humans who walked the earth thousands and millions of years before us. The German researchers believed that a small bone fragment from Siberia could be another piece to the puzzle. They worked hard to uncover secrets about the girl from the past.
The Theory of Evolution by Charles Darwin proposes that evolution occurs due to natural selection. This means that animals change over time to better suit their environment, based on a series of gradual mutations passed down from one generation to the next. From this theory, the term homo sapiens was coined, which is another word for ‘modern human’.
Homo Sapiens first emerged approximately 200,000 to 300,000 years ago and are considered early modern humans or anatomically modern humans. It has been said that the earliest known human ancestors were called Australopithecines.
Australopithecines first emerged two-to-four million years ago. They were bipedal and ape-like and had large teeth with thick enamel caps for chewing. Their brains were only slightly larger than the brains of great apes.
Australopithecines were found in Africa. It is believed that this species of human survived for about 900,000 years before reaching extinction. They vanished because of changes in their environment, by a rapidly changing climate.
The Homo genus
Another species followed the Australopithecines, placed in the “Homo” genus by some scientists. Researchers say that they had better legs compared to the Australopithecines, which resulted in better running and walking. They were also thought to have had more sophisticated brains than their predecessors.
Because of their increased mental capacity, they discovered a carnivorous diet that may have helped them adapt to changes in their environment.
The Homo heidelbergensis
The next species of human is the Homo heidelbergensis. Researchers have suggested that this species adapted well to the cold weather as their bodies were better at conserving heat. They were the first to routinely hunt for animals and build shelters. They were also the first to craft simple things out of wood and rock.
This species has been found in parts of Africa and Eurasia. Experts suggest that they were like modern people in appearance and ability – one of the reasons why they were able to perform simple tasks with tools.
More Intelligent Than Their Predecessor
Crucially, the Homo heidelbergensis was capable of controlling fire by building fireplaces. Supposedly they made this game-changing discovery around 700,000 years ago.
Scientists also believe that this was when social groups and complex social interactions became commonplace as they teamed up to take down larger animals, sharing food after a successful hunt. Despite all of these advantages, they still went extinct.
The Remnants of Our Homo Ancestor
Paleoanthropologists discovered remnants of Homo heidelbergensis during an exploration of Spain’s Sierra de Atapuerca region, led by José María Bermúdez de Castro, Eudald Carbonell, and Juan Luis Arsuaga. They called the site Gran Dolina.
The researchers at Gran Dolina dug through 11 different layers of rock. There they found various fossils of animals and humans. Reports say that on the sixth layer, the team found human remains thought to be 780,000 years old, making them the oldest human fossil found across Europe to date.
The Homo species did not have a particular physical feature that separated them from other humans. However, they did have a combination of details exclusive to hominids, particularly their teeth, cranium, and lower jaw.
Many of their traits can be compared to that of modern humans. Researchers say that the Homo forerunner had a brain approximately 1,000 cubic centimeters in size, whereas the modern human has 1,350 cubic centimeters. Homos are described as “similar to a modern human, but more robust”.
They Did Not Disappear in a Snap
Of course, even though they went extinct, they did not disappear in a snap. Fossils, evidence of their existence, have been found across Europe and Africa. Their skulls have been found in other places such as India.
Research also tells us that 390,000 years ago, in the era of the Middle Pleistocene, several species were said to have split off from our common ancestor. This might have marked the emergence of modern humans.
Rich in History
The evolution of the human-animal is rich in history, as our ancestors took many forms, including Australopithecines, Homo heidelbergensis, and eventually Homo Sapiens, showing that humans have been around for a long time.
Researchers have spent many years studying how each of these species would have reproduced. Although many studies had proven it possible, the question was – did interbreeding take place amongst early humans? It was an impossible question to answer until a group of German researchers made their breakthrough with one little fragment of bone.
Hybridization is a word that describes the interbreeding of two different species which eventually produces offspring. The offspring produced are called hybrids. Hybridization occurs in the natural world and can be a powerful evolutionary force.
Michael Marshall, a contributor at Forbes, wrote in his 2018 article that “it is a myth that two different species cannot interbreed”, citing the mule, the mutual offspring of a donkey and a horse, as an example. While the word ‘hybridization’ might be new for some, the concept has been around for a long time.
A Mule’s Tale
But mules face a particular problem. Horses have 64 chromosomes, while donkeys have 62. As you might expect, the offspring of these two animals get a total of 63 chromosomes, an odd number.
According to modern medicine, animals born with an odd number of chromosomes do not have a normal cellular arrangement. From birth, they have a genetic code that inhibits them from reproducing further. Mules cannot go on to make more mule decedents. The line stops at the first generation.
Ancient People & Chromosomes
A normal human’s chromosome count is 46. Of these chromosomes, 22 pairs are the same. One pair counts as the sex chromosome which differs depending on whether a person is born male or female. Since different species of humans only co-existed in ancient times, there are no human species left able to interbreed.
However, scientists believe that Home Sapiens began mating with Homo neanderthal after migrating from Africa to the rest of the world. From this, we know that interbreeding did take place in the past, with ancestors of those people still living today.
Europeans Had Neanderthal DNA All Along
There’s a reason that people from Asia and Europe today have at least 2% Neanderthal DNA. According to researchers, Neanderthals contribute approximately 1-4% of their genomes to people living outside the African area, including European and Asian populations.
But Homo Sapiens wasn’t just mating with Homo Neanderthal. It seems that at some point in the distant past, Homo Sapiens also coupled with those from other parts of the human species called the Denisovans.
Who Were the Denisovans?
This hominin was a recent discovery in the field of evolution. Findings of their existence were only just discovered in the 21st century.
In 2010, a team of German researchers from the Max Planck Institute released the results of their research after analyzing a tooth and finger bone found in the Altai Mountains, Siberia. They announced that they had found a new species of an ancient human.
The Name, “Denisovan”
Where did the name “Denisovan” come from? The German researchers at the site named the species in honor of the cave in which they discovered the remains.
However, it seems that the fossil they found was not enough to interpret the data thoroughly. But the researchers were in luck. in 2012, they discovered another fragment of bone in the same place in Siberia. Since then, a few other fossils have been uncovered in the caves. Through testing, it has become known that the genes of this species were carried on through people in parts of China and South-East Asia today.
Keeping Up with the Denisovans
At first, the experts have difficulty in finding more pieces of evidence of Denisovans’ DNA. There were lots of animal fossils inside the cave that made it difficult to search more for human DNA.
Samantha Brown of the University of Oxford, a well-known archaeologist immersed in the field of Denisovan research, analyzed the proteins inside the bone fragments and it was realized that the animal fossils that were found inside the cave belonged to a human, not to animals.
The Truth Slowly Unfolds
After Brown made her discovery, she was able to submit her material to Slon, a highly respected paleogeneticist. She too began investigating the DNA found deep inside the fragment. But then, a discovery was made that nobody could have expected.
The one-inch bone fragment, which would be indistinguishable from an animal bone or rock to the naked eye, came from the body of a teenage girl who was likely 13-16 years old. She died approximately 90,000 years ago. But there was more to the story.
While Slon was examining the DNA present in the bone, she was surprised by what she found. Inside were types of cellular structures made with materials that offspring can only inherit from their mothers.
Slon was ecstatic when she spoke about her findings on National Geographic in 2018. All the evidence told them that the child had a Neanderthal mother. While they expected the father to be a Neanderthal as well, this was not the case.
What’s the Problem?
“It only got more exciting when we started looking at the nuclear DNA,” Slon told National Geographic. Their knowledge of genetics told them that the answers were there in the DNA. With their bone fragment, they were close to discovering the father’s background.
However, Slon thought something was a little off about the test. At first, she doubted the validity of the results, believing that a mistake had been made. She thought that someone had altered the data without her knowledge, or perhaps that someone had spoiled the test and had attempted to make it look like an accident. Whatever the case, Slon double-checked her work.
A Girl of Two Worlds
But Slon realized that there had been no mistake. The teenage girl had a Neanderthal mother, confirmed by her DNA. Her father, to everyone’s surprise, had been a Denisovan.
Another surprise was waiting in store for the research team as they analyzed the bone fragment. Slon found the teenage girl’s genetic makeup to be remarkably varied as a whole. This is where the word Heterozygosity comes in.
Heterozygosity refers to the presence of two different alleles at a particular gene locus.
To put that in English, a lack of heterozygosity in your genes means that your parents were probably closely related. An abundance of heterozygosity means that your parents came from varied backgrounds, perhaps even different species. In that case, your heterozygosity levels would be incredibly high.
One of the Great Discoveries
The Denisova cave bone fragment told the researchers that the ancient child had parents of very different backgrounds, to say the least. Richard Green, a computational biologist explained to National Geographic that the age-old DNA was indeed heterozygous.
Slon discovered one of the most important findings in the school of evolution theory – the first generational interbreeding between species. Slon and her team were very proud of their achievement. Species interbreeding was just a concept before, but with a piece of evidence in their hands, they had turned it into a fact of history.
It Took Them Years to Prove It
Scientists thought that Neanderthals and Denisovans might have had children together, but it took years for them to prove it. Before their discovery, it was just hypothetical. David Reich, a geneticist at Harvard University noted how lucky they were to find a fossil that said otherwise.
The researchers considered their own discovery incidental. They were looking to expand their knowledge of Denisovans, yet they uncovered something new – something incredibly valuable in the field of genetics and science in general. It raised new questions on species interbreeding. How common was it? Would they find more DNA like this?
Much More Than What They Had Expected
Svante Pääbo of the Max Planck Institute told the Evening Standard that Neanderthals and Denisovans may not have had many opportunities to meet, but when they did, they made sure to mate regularly – much more than expected.
Finding the bone fragment might have just been a stroke of luck, but maybe not. There are other explanations and theories – one of which is that the two species of hominin interbred with each other on a regular basis.
Denny, the Teenager
Researchers decided to name the teenage girl Denny, a name that closest resembled the name of the place where they found her remains. Her bone was not the only piece of evidence that led to the researchers’ discovery.
In 2018, scientists conducted genetic research on a few of the fossils of ancient humans, 23 to be exact. Even with such a small sample size, the tests revealed that the ancestors of at least two specimens had a history with species interbreeding.
Besides Denny, another specimen with evidence of interbreeding in their family line is Oase 1, whose genetic makeup researchers reconstructed from a fragment of a lower jaw. This member of the Homo Sapiens group carried Neanderthal DNA.
Homo Sapiens, meaning “wise human” (possibly an ironic term) have been walking on the planet for about 300,000 years. They are the modern humans that you see around you today. Both you and I are Homo Sapiens. The oldest fossils of our descendants were found in Africa.
Oase 1’s Background
According to an article in Nature published in 2015, Oase 1’s Neanderthal ancestor was only four to six generations behind. This means that Neanderthals and other species might have been overlapped with one another.
With this in mind, Pääbo had assumed that interbreeding between different species only occurred rarely and that discoveries regarding interbreeding would be few, making verification difficult.
Now we know where Denny’s DNA came from, and which species her ancestors were. The Max Planck Institute also confirmed that the teenager’s father had Neanderthal DNA mixed in with Denisovan genes.
Pääbo concluded that ancient humans interacted, and when they did, they interacted pretty freely with one another. What an incredible discovery!
Scarcity of Fossils
Finding out about the Denisovans was the first step. However, there was a problem: a scarcity of fossils. As much as they wanted to know more about Denny and her group, their lack of further evidence meant that their research on Denisovans was incomplete.
“We aim to find out where they lived, when they came into contact with modern humans, and why they went extinct,” said project leader Katerina Douka, of the Max Planck Institute. Denisova Cave, where they first found Denny’s bone, is the sole source, and as of the moment, only a few handfuls of fossils have been found there.”
Besides bones, teeth can be used to find a person’s DNA. Scientists have done this to examine the enamel of an 800,000-year-old person.
In this study, researchers processed the proteins present in an 800,000-year-old tooth. Using its proteins, they analyzed the genetic code of the ancient man, and the results were surprising. The DNA of the enamel was so different that it did not fit the DNA of Neanderthals or the Denisovans.
Developing Ancient Humans
Researchers had assumed that interactions between these different groups happened occasionally. Due to their discovery, however, this seemed not to be the case.
How do these developments change our views of our ancestors? David Reich, the Harvard University geneticist, said “discoveries transform and change our views of the world, and this is something that we should be excited about.”
You might be wondering why first-generation hybrids are always found in limited sample sizes. computational biologist Richard Green thinks that caves, such as the ones in the Altai Mountains where some of the fossils have been found, were a well-known place for the ancient people to meet.
Caves served as “houses” for the ancient people, where they sheltered themselves from the elements. And since there probably wasn’t enough space to go around, the different species probably found themselves bunking up with strange bedfellows from time to time.
Survival of the Fittest
But was it just a matter of proximity? Or could there be something else? According to Katerina Harvati-Papatheodorou of the University of Tübingen, the cross-species interplay could have been a method of survival for the groups.
The Max Planck Institute added that usually human groups in ancient times were very small and they had a high mortality rate. Broadening their social groups was one of the few ways they could improve their chances of survival. It was a good strategy.
A Long Way to Go
Of course, over time, more information could emerge. Scientists believe that there are more mysteries around human evolution to solve. Did the Denisovans and Neanderthals simply die off when Homo Sapiens arrived? Or was there an ancient war in which the dominant side won out?
Joshua Akey, a researcher from Princeton University agrees that Denny’s DNA points the way to a new study concerning species interbreeding. But this still has a long way to go. Scientists are hoping to find more clues in the next few years.
Enrico Cappellini, a leading author and associate professor at the University of Copenhagen said that they were looking forward to the advancements of technology for research purposes. He anticipates better tools for examining protein for a DNA analysis to further their study into our ancestors and their way of life.
The University has started its funding for protein-centric research. Perhaps in the future, they will uncover more connections between humans and our origin species. Capellini is very excited about what is to come.