Name: デニソバ人私たちをより良くしてくれた不思議ないとこたち (Denisovans: Our Mysterious Cousins That Made Us Better)
Uploaded: 2021-01-14T10:39:42.000Z
Duration: 7 min 1 s
Description: VoiceTubeの動画で発音を聞きながら英語表現を覚えよう！学べる英語：

Our species, Homo sapiens, are the only humans around on Earth these days,

様態の副詞

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'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

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

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.

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

there's no guarantee we would have ever realized they were different!

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

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.

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 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,

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,

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.

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デニソバ人私たちをより良くしてくれた不思議ないとこたち (Denisovans: Our Mysterious Cousins That Made Us Better)

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