The geneticists could barely believe what they were discovering. They were looking into the recently discovered remains of a person, uncovered in an ancient Siberian cave. These bone samples had made their way to a German laboratory for examination, but no one could have predicted what the results would be.
They discovered that the remains had belonged to a little girl whose parents were two separate species. This discovery is ground-breaking as it changes everything we previously thought about genetic compatibility and inter-species procreation. Remarkably, the scientists had only just scratched the surface.
How It All Started
It all started in 2012 when archaeologists were sent to excavate a cave deep in the Siberian wilderness. In the chamber, they found a tiny bone fragment from the finger of a small person and collected the sample for further examination. But it would be a long time yet until any information of interest was discovered.
Years later, in 2015, the bone fragment was finally put under the microscope at the University of Oxford. Scientists were able to extract college from the fragment and therefore discovered that the finger had indeed belonged to a member of the biological group Hominini, a genetic subfamily that includes modern and ancient humans.
The Bone of a Revolutionary Phenomenon
The truth is, no one thought anything significant would come out of the bone fragment from the Siberian cave. It was one particular researcher called Viviane Slon, from the Max Planck Institute for Evolutionary Anthropology in Leipzig, who took an interest in the finger remains and decided to give it a proper analysis.
What she discovered when she put the finger fragment through testing threatened our modern understanding of genetics. It turned out to be so significant because no one could have predicted the results – that this bone fragment belonged to a revolutionary phenomenon and the first of its kind.
DNA Testing Revealed a Near 50/50 Split
Slon put the bone fragment under testing in 2016 and found that 38.6 percent of the DNA belonging to this person had come from a Neanderthal lineage. Aside from that, 42.3 percent had descended from a Denisovan genome, making it close enough to a 50/50 split down the middle. And it wasn’t just Slon who thought it.
According to a paleoanthropologist at the University of Toronto called Bence Viola, the near-even split of two DNA genomes was just “too good” and almost too good to be true. She stated, “You think that somebody screwed up something in the lab.” Slon checked and double-checked her findings, but each time it proved to be true.
The First Discovery of Its Kind
Slon also ensured that her results were checked by her peers, and it was confirmed to be true. This bone fragment belonged to an ancient human of two different species. It had already been understood that different species of humans had existed both before the lifetime of modern humans and during.
But we never had evidence throughout history of an ancient human existing who had come from two parents of separate species. This person was the first ever hybrid human being that had ever been discovered, so naturally, scientists and researchers were alarmed and ecstatic about the news.
Our Early Ancestors
Modern humans, also known as Homo sapiens, are known to have emerged somewhere between 200,000 to 300,000 years ago based on fossil evidence and DNA testing. Modern humans were thought to have come from somewhere on the African continent, but there had been other species of humans alongside us.
When it comes to the earliest known human ancestors, we’re looking back to the Ardipithecus ramidus hominine of around 4.4 million years ago, which exhibited both human and ape-like features. Similarly, the Australopithecus afarensis species lived somewhere around 2.9 to 3.9 million years ago and walked on two legs – think of the famous hominine fossil known as Lucy.
We Became Bipedal With Larger Brains
After our earliest known ancestors, scientists believe that the hominine tribe started to split even more into species known as Homo habilis and Homo erectus, who exhibited significant progress in tool-making as well as larger brains. Eventually, this led to our modern-day species of Homo sapiens.
It has been vital to research these earlier humans to yield a clear picture of where we came from and how we came to be. Through these archaeological findings, we have been able to understand the gradual transformation from our primate beginnings to the distinctive traits and abilities found in modern humans.
The Now-extinct Species That Started To Look a Lot Like Us Today
A now-extinct species called the Homo heidelbergensis lived somewhere around 200,000 to 700,000 years ago and looked a lot more like modern humans than our previous early human ancestors, who shared many physical traits with apes. They are thought to have been an in-between species between Homo erectus and Homo sapiens.
In truth, this human species has been discovered at many different sites, one of the most famous of which was found in the German city of Heidelberg. That’s actually where the city gets its name from. Either way, the heidelbergensis had an average cranial capacity of around 1200 to 1300 cubic centimeters, which is very close to our cranial capacity today.
Lineages From Homo Heidelbergensis Are a Hotly Debated Topic
The discovery of Homo heidelbergensis was so significant because they really did resemble modern humans more than ever before. They were even more advanced at tool-making and were able to control the use of fire, progressing them as a species more than anything before it. Things definitely got a lot more complex with the heidelbergensis species.
According to some scientists, Homo heidelbergensis is an ancestor of both Homo sapiens, AKA modern humans, and Homo neanderthalensis, AKA Neanderthals. Other researchers believe that Homo heidelbergensis has a lot more in common with Neanderthals than with modern humans, and that modern humans descended from another species.
Proof That Interbreeding Occured Between Species
As far as scientists are concerned, many different species of hominin have been living alongside each other for hundreds of thousands of years. Not only did these hominins come into contact with one another, but it is thought that some level of interbreeding between species has occurred throughout history.
Nonetheless, interbreeding between different hominin species is also known as hybridization or introgression and it is subject to debate and differing interpretations amongst researchers. But never before had we stumbled upon any definitive evidence that that was the case. That was until the remains found in a cave in Siberia were DNA tested.
Not All Ancient Human Species Could Reproduce
But it can’t be taken for granted that all the hominin species were able to reproduce with one another. While it is thought that some ancient human species could reproduce with one another, such as Neanderthals and Homo sapiens, it is speculated that reproductive isolation may occur, meaning that the offspring of an interspecies hominin could struggle to reproduce themselves.
This phenomenon is observed in the offspring born to a female horse and a male donkey, known as a mule. Mules, while considered to be animals of high endurance and disease tolerance, are generally not able to reproduce as they inherit an uneven number of chromosomes from their parents. That being said, there have been rare reports of fertile mules existing.
The Phenomenon Know As Atavism
A fertile mule is such a rare occurrence, but it does have a name. Atavism, or the term “atavistic genetic throwback,” refers to the phenomenon of male fertility. There have been cases where a mule inherited a balanced number of chromosomes from both their male donkey father and female horse mother, allowing them to reproduce.
Even if a mule is found to be fertile, they are not relied upon for breeding purposes. It is thought that their ability to reproduce and produce fertile offspring is unpredictable, and there are challenges involved in finding an appropriate mate for a fertile mule. After all, they are a complex mix of both their donkey and horse parents, and their specific set of needs can be hard to meet.
Greater Interbreeding Success Among Primates
That being said, it is thought that when it comes to primates, interspecies reproduction might be a little different. Simian animals such as bonobos and orangutans actually share the same number of chromosomes, so it is speculated that should they reproduce, they may have greater success at producing healthy offspring than a donkey/horse hybrid.
Evidence suggests that bonobos and chimpanzees have interbred twice in the last two million years, significantly altering the evolution of their present-day species. Michael Arnold, an evolutionary biologist at the University of Georgia in Athens, said about the discovery: “What they found was really cool. It adds to a growing body of work showing that species exchange genes.”
Feline Interbreeding Success Suggests Genetic Adaptability
It is fascinating t considers how certain interbreeding occurrences among the cat family have also proven successful at interbreeding. We’ve all seen those viral photos of a liger, AKA a half lion half tiger hybrid. These animals never occur naturally in the wild as the habitats of a lion and tiger don’t overlap. But zoos around the world have experimented with creating this hybrid animal in captivity.
Incredibly, the liger tends to be larger as a mature animal than its tiger and lion parents. On top of that, they also might have the ability to reproduce. They have been known to mate with other ligers, tigers and lions, shocking scientists and researchers. The Biological Species Concept asserts that two separate species will fail at producing fertile offspring.
It Wasn’t Just Neanderthals That Interbred With Homo Sapiens
Coming back to our human ancestors, it is thought that they likely shared the same number of chromosomes, making it more likely that their offspring would be reproductive and healthy. Perhaps that is why it is commonly believed that Homo sapiens successfully interbred with Neanderthals sometime between 50,000 and 70,000 years ago.
Researchers believe that this interbreeding occurred soon after hominin migration out of Africa. Of course, it wasn’t just Neanderthals that entered into the ancient human population. There was another species that interbred with Homo sapiens, which we will explore further. It’s something that scientists and researchers are still trying to get their heads around.
The Denisovans Are a Relatively New Discovery
Modern humans who have descended from a European or Asian lineage are generally thought to share about two percent of their genetic makeup with Neadnethals. These days, you can even see this appearing on modern-day DNA tests. But the truth is, it wasn’t just the Neanderthal species that interbred with Homo sapiens.
Homo sapiens are also thought to have produced offspring with the now-extinct species, the Denisovans. They lived on the Eurasian continent around 200,000 years ago, but they have only come to the forefront in recent years. In fact, they were only officially announced as having existed in 2010.
Denisovan Lineage Is More Complicated Than We Think
A group of scientists from the Max Planck Institute for Empirical Aesthetics in Germany confirmed the Denisovan species after they took a tooth and (another) finger bone fragment found in the Siberian Altai mountain. They analyzed the DNA of these bone fragments and found that yet another ancient species existed that was closely related to Homo sapiens. While the Denisovans were discovered in 2008, little was known about this enigmatic species.
A decade after the mountain cave discovery, a 2018 study in the renowned journal Cell claimed to have discovered Denisovan DNA was actually composed of multiple lineages. A paleoanthropologist at the Natural History Museum in London called Chris Stringer stated, “I couldn’t have imagined these exciting advances even 15 years ago — the pace and extent of developments has been so fast.’
The Finger Bone Fragment Was Found Amongst a Bunch of Animal Fossils
The reason why it took so long for someone to analyze the little girl’s bone fragment from an ancient Siberian cave is that it had been one of many fragments found amongst many animal fossils. It was passed over as another unremarkable piece of material retrieved from a mountain cave.
Luckily, it eventually landed in the hands of Slon, a paleogeneticist concerned with preserving genetic material from ancient remains. She was experienced in extracting information about DNA from bone fragments, but even she couldn’t have predicted how important the findings would be.
Analysis Revealed That the Teenager’s Mother Was Completely Neanderthal
The bone fragment that belonged to the ancient human species was unremarkable in size, only reaching around one inch in length. After analyzing it, Slon found that it had been the bone of a young teenage girl of around 13 years old. It was also found that she had probably lived around 90,000 years ago when a Denisovan population had lived near the Altai mountain.
It was when the mitochondria in the bone, AKA membrane-bound cells, were analyzed that more information came to light. Slon discovered that the particular cell structure found on the finger bone fragment proved that this teenage girl had descended from a fully Neanderthal mother.
Things Got More Intriguing With the Nuclear DNA
Slon spoke to National Geographic in 2018 and went into more detail about the moment of discovery. She stated, “This was already very exciting,” and added, “It only got more exciting when we started looking at the nuclear DNA.” When it came to the nuclear of the DNA, Slon was able to gather more information about the teenager’s father.
Slon stated, “That’s when we realized there was something a bit funky about this bone.” The information she received from the analysis was so strange that she actually thought she might have made a miscalculation somewhere along the line or had accidentally messed something up in the laboratory.
Slon Thought That She Had Made a Mistake
What Slon found was that there was an extremely high amount of heterozygosity present in the teenager’s genetic makeup. And this was very unusual to see. If there is a low amount of heterozygosity present in someone’s genes, it means that the parents would have been more closely related to one another.
But if, as was the case with the teenage girl, there was an extremely high amount of heterozygosity present, it would point to the fact that there had been interbreeding between two different species. It’s such an uncommon find Slon almost didn’t believe it was true. After all, it was the first of its kind.
Slon Never Thought We Would Encounter the Actual Offspring of Two Species
Slon spoke to the British newspaper the Evening Standard back in 2018, where she elaborated on how significant this discovery was. “We knew from previous studies that Neanderthals and Denisovans must have occasionally had children together, but I never thought we would be so lucky as to find an actual offspring of the two groups.”
Harvard geneticist David Reich spoke to National Geographic and stated, “It’s amazing to be able to find something like this. It seemed unlikely that we would be able to catch it happening in the act – an individual that’s really the product of a first-generation hybrid.” But it did raise more questions as to the frequency of interspecies reproduction.
This Finding Leads To a New Theory
Reich elaborated: “It’s heterozygous out the wazoo. That’s really what nails it.” Swedish evolutionary geneticist and Nobel Laureate Svante Pääbo weighed in on the finding, telling the Evening Standard, “It is striking that we find this Denisovan/Neanderthal child among the handful of ancient individuals whose genomes have been sequenced.”
Pääbo continued: “Neanderthals and Denisovans may not have had many opportunities to meet. But when they did, they must have mated frequently – much more so than we previously thought.” Because of this finding, a new theory started to emerge. Perhaps interbreeding between species occurred far more frequently than we knew.
