Breakthrough Discovery

After that, the bone passed to Slon, a paleogeneticist. And in order to learn more about this mystery hominin, she, too, began to investigate the DNA contained within the fragment. But in the end, she found more than anyone was expecting.

A 13-Year-Old Girl

At first, it seems, the bone did not appear to be anything particularly remarkable. Just one inch in length, it is believed to have come from a teenage girl who was probably around 13 years of age. It’s thought that she died approximately 90,000 years ago, when the Denisovans populated this small corner of the Altai Mountains.

Neaderthal Mother (sic)

But when Slon analyzed the DNA present in the bone’s mitochondria, she was in for a big surprise. As anyone with a keen interest in genetics knows, this type of cellular structure contains material that a child inherits only from their mother. And in this case, it indicated that the teenager was descended from a female Neanderthal.

Nuclear DNA

“This was already very exciting,” Slon told National Geographic in 2018. “It only got more exciting when we started looking at the nuclear DNA.” Our knowledge of genetics tells us that this material is passed down through both the male and female lines, and it allowed scientists to learn more about the father of this ancient teenager.

Strange Results

“That’s when we realized there was something a bit funky about this bone,” Slon continued. In fact, the results were so shocking that she was initially convinced she had made a mistake. Had she somehow skewed the data without realizing it? Or had the sample perhaps been corrupted in the laboratory?

Varied Genes

Eventually, though, Slon realized that there was no mistake. Although the teenager’s mother had Neanderthal DNA, her father, according to the analysis, had been a Denisovan. And that wasn’t all. While analyzing the bone fragment, the paleogeneticist also discovered that the girl’s genetic makeup was remarkably varied as a whole.

Heterozygosity

But what does that mean in layman’s terms? Well, it’s all to do with a concept known as heterozygosity. Essentially, if your parents were closely related – let’s say, second cousins, for example – the amount of heterozygosity present in your genes would be relatively meager. If you were the result of inter-species breeding, on the other hand, those levels would be sky-high. Make sense?

First-Generation Hybrid

And with the bone found in Denisova Cave, it was definitely a case of the latter. Speaking to National Geographic, computational biologist Richard E. Green explained of the ancient DNA, “It’s heterozygous out the wazoo. That’s really what nails it.” Amazingly, Slon had discovered one of the holy grails of human evolution: a first-generation child born of interbreeding between species.

Rare Find

“We knew from previous studies that Neanderthals and Denisovans must have occasionally had children together,” Slon told London newspaper the Evening Standard in 2018. “But I never thought we would be so lucky as to find an actual offspring of the two groups.” And at Harvard University, geneticist David Reich agreed.

Common Happening?

“It’s amazing to be able to find something like this,” Reich said to National Geographic. “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.” The discovery was so fortuitous, in fact, that it has raised questions about how common such interbreeding really was.