[♩INTRO] Our species, Homo sapiens, are the only humans
around on Earth these days, but up until recently, that wasn’t the case. You’ve probably heard of our famous extinct
cousins, the Neanderthals, who lived in Europe and
Asia. But since 2010, incredible evidence has revealed
that another mysterious cousin lived alongside early humans and Neanderthals:
the Denisovans. ...or de-NEE-so-vins, depending on whether… I don’t know. I’ve always said deh-nih-SOH-vins, but now
I’m being told it’s de-NEE-so-vins. And everything we know about them comes from
a few small bits of bone and the genetic legacy they left behind from generations of interbreeding with our
species. Our species and our cousins are hominins, a group of animals which includes us and our
ancestral relatives basically, anything more closely related to
us than to chimpanzees. During most of the past 2 million years or
so, there were several species of hominins on
Earth at any given time. And in the past few hundred thousand years,
before our species outlasted, or outcompeted, or just killed all the rest,
our ancestors lived alongside Neanderthals and at least one other
species of human. The first evidence of these extinct hominins
came from a single finger bone discovered in Denisova Cave in Siberia. From the shape of the bone, researchers could
tell it was some sort of hominin, but that bone by itself wasn’t enough to
identify what species it was. So, they sequenced the DNA from the bone, hoping to determine if it came from a Neanderthal
or a member of our species. But the DNA found was strikingly different
from both of those. It belonged to a whole other branch of our
family tree. Researchers named the newly-discovered hominins
Denisovans after the cave where that revealing pinky
bone was found. And since then, only a few scattered fossils
of them have been found… and almost all have come from that same cave. There were three molars, for example, which were identified as Denisovan from their
DNA. There was also a small fragment of a limb
bone reported in 2015 that turned out to be from an individual with a Neanderthal
mom and a Denisovan dad! And in 2016, scientists discovered a fragment
of braincase from Denisova Cave. In fact, the only Denisovan fossil we’ve
found to date anywhere else is a partial jaw. It came from the Tibetan Plateau, around 1,500
miles south of cave! So it seems these cousins of ours were pretty
widespread across Asia. And yet, that’s all the physical evidence
we’ve got that they existed. A few teeth and some bone fragments are all
of the fossils known for Denisovans as of the summer of 2019. If it weren’t for DNA analysis, there’s no guarantee we would have ever
realized they were different! And with so few remains, paleoanthropologists can’t actually properly
describe them as a new species just yet. In order to do that, they would need enough
bones to compare and contrast with other species, to clearly list what features make them distinct. This lack of fossils also makes it difficult
to understand what Denisovans were really like. We know they inhabited Denisova Cave for a
long time, since the fossils found there range from 300,000
to 50,000 years old. And there are also tools and artifacts known
from those same deposits, but it’s impossible to say so far whether
those were the work of Denisovans or Neanderthals, whose remains have also been
found in the cave sediments. Some of those tools might even have been the
work of our own species, although so far, no definite Homo sapiens
fossils have been recovered from the cave. With only DNA to go on, it’s tough to answer
these questions about Denisovan lifestyle, culture, or appearance. But that DNA alone can tell us quite a bit—and
not just about Denisovans. If you’ve ever had your own DNA tested, you may have learned that you have a bit of
Neanderthal in you the result of a long history of our ancestors
interbreeding with Neanderthals. Well, you may have some Denisovan DNA in there
as well! You see, the DNA we’ve sequenced from these
bones has revealed a history of gene-swapping between Denisovans, Neanderthals,
and our own ancestors. Denisovan DNA is especially common in the
modern human populations of Southeast Asia and Melanesia, making up as
much as 4% of their genome. In fact, a study in 2019 more closely examined
the Denisovan genes found in the people of Papua New Guinea and Southeast Asia, and found evidence of three separate lineages
of Denisovans. That means Denisovans were much more diverse
than scientists originally thought. There might even have been multiple species
of them! Those same analyses also suggested some interbreeding wasn’t all that long ago, as recent as 15
to 30,000 years ago. If true, that would mean Denisovans survived
at least as long as Neanderthals, and only disappeared right before the end
of the Ice Age and the rise of modern civilization. And even though they’re long gone, they
still help us out today in unexpected ways. For example, there are specific genetic mutations found in modern Tibetan people that help them
regulate hemoglobin levels in their blood so they can survive better
at high altitudes. These mutations aren’t seen in most other
living humans, but they are found in Denisovan genomes. Researchers think that’s where these genetic
traits first evolved, perhaps for their own high-altitude lifestyles, and then our species picked them up through
interbreeding. Similarly, there are gene variants found in
Inuit populations that promote the development of heat-storing brown fat, which
comes in handy in cold climates. Those genes, too, bear a striking resemblance
to Denisovan genes, and may also have passed by them to us. Other genetic variants relating to things
like our immune systems and skin color have also been identified as
possible Denisovan genes. And since these traits ultimately became common
in our species, researchers suspect they may have helped our
ancestors defend against diseases or withstand new environments as
they spread through Europe and Asia. But until we find more fossils, the exact extent of their influence on our
genomes will remain unclear. Since 2010, there has been a whirlwind of
new discoveries and revelations about Denisovans, but these relatives of ours still remain shrouded
in mystery. Scientists are on the lookout for more fossils,
especially ones that would help us nail down what they looked like and what their
culture may have been like. With enough of them, scientists might even
be able to give Denisovans an official species name. And more genetic studies will help us further
sort out how our species benefited from consorting with other human
species. Because one thing is increasingly clear: we definitely did not come to be the way we
are today all by ourselves. Thanks for watching this episode of SciShow! If you liked learning about Denisovans and
their enduring genetic legacy, you might like our episode on what Neanderthal
DNA is doing to our genomes. Ancient humans, amirite? And if you just want to keep on learning all
sorts of sciencey things with us, there’s probably some related videos in
the sidebar. I think they’re over that way. There’s also the subscribe button. There? Is it there?! [♩OUTRO]
